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Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics

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Posted on October 5, 2013 at 09:06:54
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
I've been busy of late concentrating on another FRT configuration which is a pretty big improvement over those I've previously posted here about. The sketch below shows the concept. Sorry it's so busy, but there is a lot going on and I tried to capture the most relevant bits. Briefly: the FRTs prevent the left ear from hearing the right hand side tweeter, and vice versa by using parallax. As a result, it approaches ambiophonics in crosstalk cancellation of the critical high frequencies. It definitely is a one person, head-in-a-vise experience, but not only does it increase envelopment, it also makes the phantom center sound as clean as a mono signal from a single speaker, which is to me an important goal. In short, it is like having the absolute best features of headphone listening (the definition of crosstalk elimination) without the band-in-your-head phenomenon. Oh, it also has the effect of reducing the volume of the phantom center by up to 3 dB, which in the case of most recordings is probably a good thing. :) Best of all, you don't need to bring a mattress into the room, stand it up between speakers, and rest your head on its edge! I actually tried using wood to use MMGs in a textbook ambio setup a while back, but it failed miserably. My new setup, however, works! And no, no additional DSP, just FRTs. The FRTs also have the benefit of breaking up room nodes, making it a bit easier to EQ the room response "flat".

I use the Moody Blues' "Days of Future Passed" disk as a way of testing hall depth reproduction and detail retrieval. Specifically, the first track has some very low level harp and celeste glissandos in the first minute which I can clearly hear on my AKG 240 headphones but were inaudible on my Gunned MMGs. Up to now, I ascribed that to not having 1.x or 3.x Maggies, known for superior detailing. Well, guess what? Those glissandos are now clearly audible on my MMGs!

Here's the sketch of the layout:



Again, apologies for the busyness of the sketch. In order to clearly show the slight of hand in blocking crosstalk, I could only fit the left speaker details on the sheet. Maggies are ideally suited for this treatment, btw, since the tweeter is located on one edge. By placing the tweeters "in", a single 4 foot wide by 6 foot high panel can be placed so that, in nearfield (seated about 5 feet 6 inches away from the speakers, which are spaced a bit less than 7 feet apart) the left tweeter is blocked from being directly heard by the right ear yet the left ear has an unobstructed "view" of that tweeter. In addition, the rear portion of the FRT behind the speaker acts like all the other FRTs I've written about, blocking the first reflection off the front wall from reaching the listening position within the first 10 milliseconds. And by toeing in the MMGs as shown, side wall first reflections are eliminated as a concern. Yeah, this does nothing about rear wall early reflections, but my experience has been that if you manage the front and side early reflections, the sonic benefits are significant.

The presence of the FRTs changes the bass modes in the room; a massive suckout at about 80 Hz without them virtually vanishes, but a new one at 160 Hz pops in, although it isn't as deep. In my system, I'm using the Behringer DEQ2496 to "flatten" the response at the LP anyway, so the end result is a smooth response.

Here are some photos:



This shows the right MMG from the listening position (LP). Apologies for that blasted vertical shadow in the foreground. I hope you can tell that the entire grill cloth of the MMG is visible; this represents the view of the right eye (left eye closed) showing that the tweeter has an unobstructed path to the right ear.

Also note the cinder blocks raising the MMG, and the fact the MMG is shimmed to be almost perfectly vertical. I find a hint of tilt-back aids in fine-tuning the sound. YMMV, of course. Also note the other cinder block propping up the FRT to keep it from crashing down. :o



This pic represents the view of the left eye (right eye closed) from the LP. Note that a few inches of the left side of the grill cloth are hidden behind the FRT. This is where the tweeter is. Thus, the right hand speaker's tweeter is prevented from being directly heard by the left ear.



The LP :) Note the electronics easily assessable on the low table adjacent to the seat, and that the LP is about 36 inches from the rear wall. Also note the measurement microphone for flattening frequency response; I swing it into position centered at the rear cushion of the seat when in use. And no, I'm not a closet karaoke fan. :)



Another view of the cinder block propping up the FRT, and the Armaflex butyl (sic?) pipe insulator I use for edge diffraction effect elimination on the rear of the FRT. It's optional, but the other piece of pipe insulation between the MMG and FRT is mandatory, both to protect speaker finish as well as to keep the FRT from buzzing. The Armaflex does a good job of that.



Better view of the Armaflex protecting the MMG and isolating the FRT acoustically.



View from LP of the front wall mirror, showing that the MMG driver is not visible due to the FRT.



Sorry for the dark image; this is the side wall mirror showing the MMG edge on to the LP.

If you only try one of my many FRT configurations, make it this one. The improvements in phantom center and low level detail retrieval are well worth it.

MG-bert

 

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RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 5, 2013 at 09:32:03
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
One additional thought: Floyd Toole's book "Sound Reproduction: Loudspeakers and Rooms" has an entire section (9.1.3) which he calls "An Important One Toothed Comb - A Fundamental Flaw in Stereo" which relates to the crosstalk phenomenon which, I can attest to from experience, this FRT configuration directly addresses.

Use the link below to scroll to pages 151-155.


MG-bert

 

hmm… some of it …, posted on October 5, 2013 at 20:22:37
Mart
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Posts: 31271
Location: upstate NY
Joined: June 6, 2001
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  Since:
June 25, 2000


... just my 2¢
moderate Mart

Planar Asylum

where speakers are thin & music isn't

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 5, 2013 at 21:48:55
Green Lantern
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  Since:
June 17, 2003
interesting configuration; is this for a mono set up?

*scratch that, I see the reference about space constraints on your paper for both speakers! Would be interesting to see the pair though-


 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 5, 2013 at 23:42:43
JBen
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Posts: 2768
Location: South FL
Joined: May 18, 2008
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July 26, 2010
LOL, you use the pipe insulation and Armaflex in ways close to but not quite the same as some of us use these for.

Old Guy 42 and I are jointly evaluating a few related tweaks that should lend themselves for some cheap and fun approaches. To be sure, the use of those circular pipe edges brings some advantages, which is part of what Old Guy 42 and I have been exploring. However, those who try them may wish to fine tune their respective results. For this, they may need to add hard edges to avoid top-end clarity and dynamic impact loses.

For example, my MMGs have had Armaflex butyl (2" tape) along the front of the frame and rounding it around the frame edges for years. Yet, I have not found a way to leave the outer edges exposed; always need to add a hard edge like the factory trim.

Yet, in your setup, it appears that the soft butyl pipe insulation edge doesn't do this? If so, it could be a function of your whole setup as a system, which would be very interesting!

 

RE: hmm… some of it …, posted on October 6, 2013 at 07:50:02
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
"...sounds vaguely familiar"

@Mart:

Yeah, you posted that years before I became an inmate here. I did find it while looking up placement strategies when I first got my MMGs back around 2009. Just goes to show that one can't necessarily come up with a totally novel setup - after all, yours relies on the rule of thirds and a 60 degree equilateral triangle! The idea of cancelling out sidewall early reflections is a powerful one for dealing with a small listening room, though, and one that I'll gladly give you credit for.

OTOH, I've yet to see anyone crazy enough to play with Luann panels propped up at crazy angles in a Planar listening room. So if I'm claiming any original thought here, it's solely with those.

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 07:58:52
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@Green Lantern:

"interesting configuration; is this for a mono set up?

*scratch that, I see the reference about space constraints on your paper for both speakers! Would be interesting to see the pair though-"

Quick answer: print out the sketch and hold it up perpendicularly against a mirror on the right so the left side I pictured is reflected in it. Voila! ;-)

As for a photo of the entire thing, the arrangement is so crammed that it was all I could do to capture the images I did - even fully wide angle on my Nikon Coolpix camera only shows so much, so I had to piecemeal it. And no, my MMGs are NOT banana shaped - it's the wide angle lens doing that.

MG-bert

 

RE: hmm… some of it …, posted on October 6, 2013 at 08:31:28
Mart
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Posts: 31271
Location: upstate NY
Joined: June 6, 2001
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June 25, 2000
The thirds bit merely happenstantial when I did a square room.   The issue that drove it was equating the space behind your head to the space behind the dipolar speaker to minimize comb filtering... or, so says the math.

P.S.:   Still have internal tweeters if your near a side wall, YMMV.



... just my 2¢
moderate Mart

Planar Asylum

where speakers are thin & music isn't

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 08:32:24
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@JBen (and OldGuy42):

"Old Guy 42 and I are jointly evaluating a few related tweaks that should lend themselves for some cheap and fun approaches. To be sure, the use of those circular pipe edges brings some advantages, which is part of what Old Guy 42 and I have been exploring. However, those who try them may wish to fine tune their respective results. For this, they may need to add hard edges to avoid top-end clarity and dynamic impact loses.

For example, my MMGs have had Armaflex butyl (2" tape) along the front of the frame and rounding it around the frame edges for years. Yet, I have not found a way to leave the outer edges exposed; always need to add a hard edge like the factory trim.

Yet, in your setup, it appears that the soft butyl pipe insulation edge doesn't do this? If so, it could be a function of your whole setup as a system, which would be very interesting!"

Short answer: yeah, it's a total system thing going on here.

Longer answer: I'm only using the pipe insulation in 2 places - where the FRT leans up against the speaker, and on the rear edge of the FRT closest to the front wall. In both cases, these do not have any direct effects on the primary sound. In fact, the FRT is positioned such that any sounds which might be affected by the pipe insulation between it and the MMG are delayed from reaching the listening position (LP) for a LONG time, acoustically speaking; ditto the rear FRT edge insulation. In fact, the only reason to use pipe insulation between the MMG and FRT is to dampen vibrations and keep the panel from buzzing along to those wonderful bass notes. ;-)

Just in case I wasn't clear about the point of this mod, it is to get the most out of Maggies (and possibly other planars) in a small, square room - the kind of room that wise Planar enthusiasts would insist they would not work in, for all kinds of technically sound reasons. Well, I'm an engineer, and I make a living tricking Mother Nature into doing things (while following Her rules) that give results which would not normally be possible. People cannot walk on air, but build a bridge and effectively you're doing that as you cross a river valley, for instance. Acoustical engineering is not my specialty, but I realized that the laws of reflection and incidence apply for higher frequency sounds - the ones most critical for localizing phenomena in space. Hence the FRT concept.

My trickery in this case is 2-fold: 1) use panels angled such the early reflections of mid-to-high frequencies from front and side walls are delayed to be greater than 10 milliseconds from the initial signal, and 2) to use the forward part of the FRT panel closest to the LP to address what Floyd Toole himself called "An Important One Toothed Comb - A Fundamental Flaw in Stereo". When I came up with that idea, tested it, AND FOUND IT WORKED, I was excited. Still am.

BTW, I'm with you that the forward edge of the FRT mist not have any Armaflex on it, partly for the reasons you cite.

BTW, in the credit-where-credit-is-due department, thank you JBen for introducing me via an earlier post to Armaflex. It really is versatile stuff.

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 16:07:57
DreamOperator
Audiophile

Posts: 67
Location: Denver, CO
Joined: April 20, 2012
Interesting. Reminds me of the Jecklin disk.

http://en.wikipedia.org/wiki/Jecklin_Disk

The main difference being that the above is made out of a soft, absorbent material, while your FRTs are solid and reflective.

Have you thought of or tried using a soft, absorbent material?

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 16:56:21
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@DreamOperator:

The point of the panels isn't to absorb sound - it's to deflect reflections so the time they take to reach the LP is greater than 10 milliseconds - actually it's longer for a lot of these. That way, the essential character of planars is maintained, vice turning them into a very large pair of mini-monitors.


MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 18:53:35
DreamOperator
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Posts: 67
Location: Denver, CO
Joined: April 20, 2012
I see what you're saying. I'd like to try this sometime.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 6, 2013 at 19:19:26
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@DreamOperator:

Go for it! It's a real cheap experiment, and it really cleans up already good sonics!

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 7, 2013 at 21:11:13
JBen
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Posts: 2768
Location: South FL
Joined: May 18, 2008
Contributor
  Since:
July 26, 2010
MG-bert, I know the challenge that you are so creatively tackling. It can't be easy, if I judge by a little on-the-fly experiment I did.

Last year my neighbor had to rebuild a long wall that became water damaged. A load of drywall was brought in for the project. However, the contractor was delayed; hospitalized for a few days after an accident. So, I asked my neighbor to loan me a few pieces of the drywall for a day.

With it, I "shortened" my room from 12x25 or so to 12x12. It was an audio disaster compared to its usual sound. I suppose that I could have fixed some of the things that changed so radically. In fact, had I had more time I would have applied some of the lessons you had already shared, for I remembered your earlier posts on the subject.

With this in mind I was about to ask my neighbor for an extra day. Just then my wife, who had gone to visit her mother, called. She decided to return earlier than planned.

That was the end of the experiment right there. LOL! Had she walked in while the mess I made was still on...I would have joined my neighbor's contractor in the hospital.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 8, 2013 at 18:09:55
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@JBen:

"MG-bert, I know the challenge that you are so creatively tackling. It can't be easy, if I judge by a little on-the-fly experiment I did.

Last year my neighbor had to rebuild a long wall that became water damaged. A load of drywall was brought in for the project. However, the contractor was delayed; hospitalized for a few days after an accident. So, I asked my neighbor to loan me a few pieces of the drywall for a day.

With it, I "shortened" my room from 12x25 or so to 12x12. It was an audio disaster compared to its usual sound. I suppose that I could have fixed some of the things that changed so radically. In fact, had I had more time I would have applied some of the lessons you had already shared, for I remembered your earlier posts on the subject.

With this in mind I was about to ask my neighbor for an extra day. Just then my wife, who had gone to visit her mother, called. She decided to return earlier than planned.

That was the end of the experiment right there. LOL! Had she walked in while the mess I made was still on...I would have joined my neighbor's contractor in the hospital. "

LOL! That's why in my castle, the rig lives in it's own outbuilding... er, shed. My better half never goes there, and since it's a shed, the pressure is off to neaten up either during or after an experiment. Besides, that way I don't have to introduce the Maggies to our cats...

And wow! A full 12' X 12'! At least 20 square feet bigger than my space. Can't imagine what you did with all that extra room! Oh wait, you have the truncated corners, don't you? That would complicate a nearfield setup a bit.

Anyway, thanks for the kind words about creativity. We just rewatched the "Dinner with Schmucks" movie; am I a candidate? ;-)

I apologize if I already posted the link below, but a while ago I had the good fortune of having a pair of Maggie-owning audiophiles who regularly post on the Planar Circle come out to the wilds of Western Maryland to visit the shed. Although this was before I came up with the present FRT configuration, they did hear my so-called mini-FRT setup. Spoiler alert: they seemed to be impressed, and I am proud of what got pulled off in my tiny space. Maybe you can compare what you heard in your room to their take?

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 8, 2013 at 19:03:28
DreamOperator
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Posts: 67
Location: Denver, CO
Joined: April 20, 2012
I have some 4'x2'x4" fiberglass panels with solid wood on one side.

I took a pair of them and placed them as to block the left tweeter from the right ear and vice versa. Wood side facing the closest speaker.

While the rear reflections were not altered and there was a ton of absorption going on in the middle, I was able to get some sense of the effect. Lots and lots of depth and very clean separation.

Perhaps I'll play around more down the road. Thanks for sharing.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 9, 2013 at 01:13:24
JBen
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July 26, 2010
MG-bert, I read the whole thing a couple of times trying to relate to what I heard here when I "reduced the room". Other than being glad that your system performs so well, I am not sure I got enough details to compare to your un-EQ'd config. I do remember what went wrong vs my normal room config, though.

Here is what I remember. Please keep in mind that I use no equalizer or DSP. The nearest thing to it is the ability to raise & lower the tweeter at the PLLXO biamp interface (and this did not help me at all). In addition, I tuned the 1st/2nd order PLLXO points IN THE NORMAL ROOM...which is EQ of sorts.
1. Ordinarily, I have to tame bass somewhere in the 65-80 hz range in this room because the speaker on the right side sees a solid concrete wall. I have acoustic ways to do this. However, the square room overwhelemed my normal measures. The normally strong but acceptable peak now zoomed to offensive boominess.
2. After much work, I have the 100-250hz range real good, full and texture-rich. Well, the square room ALSO ruined this. However, since I could not measure that day, all I can say is that trombones, tubas, cellos and other instruments lost their proper heft, texture & presence. EXCEPT as they went higher up into the upper-bass/low-mids range. Somewhere there, a peak must have risen...quite strong and annoying.
3. In those days my system had already acquired most of its current slammy dynamics that can actually hit you perceivably and shake the sofa cushions at times. This went out the window. The forward impulse got lost.
4. The lower bass 40-60hz went AWOL...probably drowned by the peaks higher up. I don't use the subwoofer for music but suddenly I felt like it was needed badly. I turned it on just to see but turned it off right away...too messy & muddy at the setting it normally has.
5. Overall soundstage and soundfield, which normally enlarges the room and "erases the walls" was severely hampered, though not wiped out. I have heard some Maggies do worse when in over-damped rooms.
6. Imaging within the soundstage lost its compelling ability to "be looked at". Normally, it is not just solidity. One can also turn the head and look from side to side and the 3D elements stay put. Not so with the experimental 12x12 "room". To be fair, I've heard far worse from my own system in the very early days...and some friends thought it was great in those days...go figure!
7. The upper midrange and top-end did not suffer severly as far as "peakiness". I was not impressed by them but it may have been that I was a bit too fixated on what happened elsewhere in the lower range SQ.
8. The upper midrange and top-end did not lose much clarity either, I felt that it would have been easy to "re-tune" for the "room change".
9. The center imaging remained surprisingly solid, though much shallower.

My neighbor made a comment that stuck in my mind for being very true. He said that the speakers sounded much smaller.

So, you see. In reading about what you have accomplished so far in an even smaller space I can appreciate the effort it took. I think folks should take a look at your approach and adapt what may be needed for their places. I certainly would.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 13, 2013 at 07:03:06
MG-bert
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Posts: 130
Location: Maryland
Joined: January 18, 2009
@JBen:

Sorry for taking so long to respond. Remind me never to ask you to do something - you'll spend hours and hours doing it! ;-) I really appreciate your feedback here, if for no other reason that it does validate the fact that making Maggies "sing" in a small, boxy room is a non-trivial exercise.

That said, I would dearly love to hear your setup someday. I still have not been able to achieve the really 3D pinpoint imaging you describe. Earlier, you gave us a guided tour through the first minute of the Eagles "Hotel California" from "Hell Freezes Over", and while I get pretty good depth, I don't get the whistle coming from the balcony over my head at one point like you described. On the other hand, I do get the occasional sense of instruments in front of the plane of the speakers, and since those are about 5 feet away, that is CLOSE! Also, I can localize the relative height of instruments.

One track which seems to be out of print now by a little known band called Mostly Autumn ("Shindig" from "Spirit of Autumn Past") has a jaunty synthesizer bass beat coming from my feet! Literally goes from left foot to right foot and back and forth. Then a fiddle comes in, a little above ear height and behind the plane of the speakers on the right, then a flute on the left forward of the speaker plane... you get the message. Lots of fun.

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 13, 2013 at 07:11:45
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@DreamOperator:

De Nada; I see posting here as a way of publishing findings, with the hope of getting them "peer reviewed". So thanks for filling in that part.

I just realized there might be a far less intrusive way of accomplishing the "ambio" trick. Need to make another trip to the hardware store, which might only happen in the next week or so... Would be great to increase the WAF factor from the imaginary number the current FRT configuration currently has!

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 13, 2013 at 08:20:59
JBen
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LOL! I do take my time testing some stuff. BTW, I did run "Hotel California" during that square room test. It was nothing like I am used to. It does remind me that, at the time, I though that perhaps I could have applied heavy damping to the "new wall" behind my seat. I have learned to respect what happens in the space behind my seat, for it helps those recordings that capture ambience and fuller soundfield. It also seems to help with dynamics a little. Come this Christmas, I know that the Christmas tree will bring a little more than a shade for the usual presents. It always helps overall SQ.

Incidentally, "Hotel California" was also at work last evening. I had just returned from a trip. Before leaving, I had begun to test a tweak that Old Guy 42 had encouraged me strongly to try. Initially, last week, it seemed really good. However, it takes a few rounds of something before I am convinced that I am not having "audio fantasies".

So, I ran a few hours of music after my trip (and a nap to recover). It was all good. The tweak may further allow me to enjoy most of the best that my system can only -- until now -- do during the coolest months in South Florida. These are the days when lower temps allow many folks to turn off their A/Cs...so there is less ambient & powerline noise. The tweak also seems to help my system at the worst of it all. I have a park close by. On evenings when they turn the many large floodlights on...I can tell without looking.

It will not help everyone but the tweak is simple and has been known for a while. I'll let OG42 tell about it, for I encouraging him to do so, and I've gotta run to help a friend with his system now.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 14, 2013 at 07:16:35
MG-bert
Audiophile

Posts: 130
Location: Maryland
Joined: January 18, 2009
@JBen:

You said:

"LOL! I do take my time testing some stuff. BTW, I did run "Hotel California" during that square room test. It was nothing like I am used to. It does remind me that, at the time, I though that perhaps I could have applied heavy damping to the "new wall" behind my seat. I have learned to respect what happens in the space behind my seat, for it helps those recordings that capture ambience and fuller soundfield. It also seems to help with dynamics a little. Come this Christmas, I know that the Christmas tree will bring a little more than a shade for the usual presents. It always helps overall SQ."

In the FWIW department, I have tried putting absorption on the wall behind the listening seat, and I have to rip it away. There is a huge difference between delayed reflections coming from behind and NO reflections coming from behind. Sounds totally unnatural. And, it's my theory that human evolution has conditioned our hearing to be able to deal with early reflections (less than 10 milliseconds from the initial impulse) coming from behind differently than those coming from the front or side. Think of seeing an acoustic guitarist in a fairly small club, and you sit along the rear wall. You'd just be aware that you're in the back, but the impact on sonics should be minimal.

Having said that, I would kill for a larger space to set up my MMGs, because I believe you when you say that the space behind you allows for a rich tapestry of later reflections to help solidify the reality of the performers in the room.

FRTs do help in my box, though!

And OldGuy42, what's your great idea? I'm all ears!

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on October 14, 2013 at 09:58:18
old guy 42
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Hey MG;

MG wrote..."And old guy 42, what's your great idea?"

This is definitely NOT my idea. I'm a no-tech old man that loves music.

I found this "idea" in the Tweaker's Asylum. (see link) The RCA shorting plugs are for analog INPUTS ONLY, as Jon's post states. I also used a 75 Ohm "terminating" RCA plug on the SPDIF output of my CDP, again, according to Jon. The "shorting RCA plugs" replaced the Cardas caps I have used since 2005.

A very nice improvement in imaging and detail on my old stuff. But, as you know, with these things, YMMV.

Also, again, a nice job with your FRTs!! If I have the good fortune to fall into a dedicated room, I will try your ideas, for sure.

Again, do NOT use a shorting RCA plug on an analog OUTPUT!!!

Take care....old guy

 

RE: I'm all ears!, posted on October 14, 2013 at 11:46:29
JBen
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That, my friend, is a great thing to do and should serve you well. We all fail to "unplug them" enough from time to time and thus fail to tap some opportunities.

OG42 and I are exchanging tweaks -- new and old -- these days; dusting off some known ones and even inventing others. By using some similar music to correlate observations we can better tell what's promising to share.

In any event, it serves me well, I have to say. There are a few tweaks out there that we all may have seen with interest but not really tried, for any number of reasons. Well, OG42 brought this simple one to the foreground and insisted that I try it. I am very glad that I did.

While "YMMV" does apply, it is so easy to try that it should be worth doing so. Cheap that I am, grabbed some bags of Radio Shack item #274-321 and shorted the plugs with a drop of solder...it worked like charm.

[As warned before by others: DO NOT SHORT RCA OUTPUTS]

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on August 12, 2014 at 06:44:40
pistonengine
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I would think the side and front wall reflections could be effectively managed using diffusors/absorbers. I'm wondering if the key to this concept is the direct path blocking of the tweeter, like you detailed. It looks like you definitely need the tweeters in to accomplish that.

I'm wondering if that can be accomplished for those of us who enjoy a pretty living room :D

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on August 12, 2014 at 20:15:04
MG-bert
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@Pistonengine:

IMHO: The problem with absorption is that the first reflections go away; you kinda want them, only later. And diffusion still allows some early reflections to get by. My scheme traps the reflections, delaying them a bit. For a really small room, I think my FRT arrangement allows the most of what constitutes Maggie Goodness to shine.

The direct path blocking of the tweeter was a really nice plus to this configuration; the way it cleans up crosstalk, something most don't realize is a form of distortion until you hear its absence.

And nothing says the FRTs can't be more decorative; plexiglass panels, perhaps?

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 10:39:49
josh358
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OK, so somehow I'd missed this thread when it first appeared. As it happens I've been experimenting with an RFZ so I have some 4 x 6 pieces of styrofoam to play with, and after following the link in the 1.7i thread here, I had to try this.

The mid-tweet panels of my IVA's are already oriented to cancel the sidewall relection. Unfortunately the current setup geometry didn't permit me to try the ambio trick and RFZ barrier simultaneously so I decided to try them independently, RFZ barrier first:






Well, it hit the ball out of the park! The speakers are already 6' out from the wall and displaying good depth, but with the barriers in place, the remaining confusion was gone and the image just seemed to stretch back forever. This was despite the fact that according to the mirrors, the barrier was giving me a sidewall second reflection.

I couldn't compare the barrier with my QRD diffusors because I painted them yesterday and the paint is still trying, but I hope to do that in the next few days.

Next, I tried pulling them forward to make a quasi-ambio barrier. That wasn't as successful -- I heard a bit of an improvement in image width but not what I was expecting. I hadn't read your full post though at the time and I may have been sitting too far away -- 8' rather than in the near field as you describe. I'll have to experiment more systematically with both when I have the time.

Finally, I decided to compare that with a full ambio barrier:



I heard the expected widening of the sound stage. It wasn't actually super wide on the recording I listened to (Kurt Masur playing Tchaikovsky's Serenade for Strings on Teldec), but the sides of the stage were natural, as they never are in conventional stereo, which either truncates them at the speakers or provides an unnatural fuzzy widening from early sidewall reflections. But what really got me was what happened to the phantom image -- it gained definition and turned rock solid, like three-channel stereo but without the lacunae that occur between the center and the sides. (I'd then only skimmed your post and hadn't read the first paragraph, where you mention the same phenomenon -- I was delighted to see when I came back downstairs that your observations confirm mine.)

So very promising and I'm looking forward to more experimentation. I'm not sure how practical the ambio barrier is though I love the effect of the full barrier and I'll definitely experiment more when I have the time. But the RFZ barrier is far and away the best results I've had with these speakers in my 12 x 14 room, doesn't block the window like diffusers, and would be behind the speakers where you don't really see the barriers. So if this proves the best setup, I can see making a couple of Plexiglas gobos and making the installation permanent.

Very impressive, particularly since I haven't had much luck in my ambiophonics experiments in the past, either with a foam mattress barrier or with crosstalk cancellation, which always seems too tweaky. (Of course, this makes me think that planar technology is ideal for making a phased array -- and that with head tracking, you could aim the higher frequencies at the appropriate ears and then use crosstalk cancellation at the lower frequencies where the wavelength is long enough for it to work well . . . )

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 11:42:08
Satie
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The deflectors you put up look to protrude a great deal ahead of the tweeters, I wonder if you tried this without the protrusion, with the deflector board put back to the edge of the frame where it does not interfere with the front output.

Also wondering about how far you need the back portion of the board to extend to get the full effect.

As to how far forward the board extends- do you leave it just short of intruding into the line of sight to the tweeter? When I experimented with this before, the results were very dependent on how much reflection you had from the opposing sidewall before you placed the deflector. If the opposing sidewalls were not uniform and reflective, placing the board ahead of the tweeters made less of a difference. So I proceeded largely with control of the backwave alone, without redirection of the front output away from the opposing side wall.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 11:47:33
Norman M
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I'm not sure if this pertains to your set-up but in MG-bert's post the Left Speaker - Right Ear (and v.v.) cancellation is the basis for Carver's Hologram Generator (C-9 as well as in other of his products). It can be engaged/disengaged by the press of a button, so I'm able to make instant comparisons. I liked the C-9 since first available in my pre-Maggie days (before 1975) when listening to Acoustic Research 3 box speakers and in many, but not all recordings it also adds to my listening satisfaction with Tympani IV-As.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 12:55:48
josh358
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I remember the Carver! I never had one myself, but I did get the demo disk. It is very much related to the electronic versions of ambiophonics, in fact, as far as I know, it's the basis of them -- I don't know if Carver invented crosstalk cancellation, but he was the first to sell a consumer audio product that does it electronically. There have also been some loudspeakers that do it by directing an out-of-phase signal to drivers on the opposite channel loudspeaker.

The ambiophonic barrier does the same thing mechanically but isn't really practical in its usual configuration because it's practically touching your nose.

Come to think of it, I haven't tried the ambiophonics software (you can get it free online) with the IVA's yet. I did try it with my MMG's without much success. You might want to give it a try, it's more advanced than what Carver could do with the tech of the time.

Really interesting that it works with your IVA's, you've inspired me to give it a try.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 13:16:49
josh358
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I didn't try them further back because the woofers were in the way, but I did try another angle in an attempt to minimize sidewall reflections. It didn't work as well for reasons I don't know. I think the next step is to experiment nore systematically, beginning with MGbert's ray tracing diagram, but of course I'll have to figure out how to accommodate the woofer panels.

Extension of the board behind the MT panel -- I'm guessing the more the merrier because at lower frequencies you're going to get diffraction so the barrier will be effective only when it's large compared to the wavelength. I just had them extended sufficiently to completely block the reflection of the panels in the mirror, so a few inches beyond the actual driver.

Extension of the board in front of the panel -- if you look at the photo from the listening seat, you can see that they were extending in front for the RFZ experiment they didn't occlude the drivers at all. For that purpose, flush with the front would presumably be better because you wouldn't get diffraction at the proximate edge.

In the parallax barrier experiment, I had the boards positioned so that I could see the tweeter with the proximate eye but not the distal one. One of the reasons it may not have worked as well as MGBert's setup is that he was using MMG's, which have a lower XO to the tweeter -- my barriers were only effective from 3 kHz up. Interesting about the effect of the sidewalls. Mine are both irregular and reflective, not sure how to characterize them.

Why did you give up on your barrier? I still have some other options -- Fresnel reflector (which however is a major production), polycylindrical diffusors (but again, that's a major production since to preserve the window, I'd need to bend Plexiglas), and of course the QRD's. Or I could just move to somewhere with a bigger listening room. :-|

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 19:05:55
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Hello,

I am using Ambiophonics method for about 5 to 6 years. I just got to know about this forum and thread through Google alert.

I use Sound Lab ESL speakers. I first discovered Ambiophonics early 2000s and experimented with a mattress. I am currently using AmbiophonicsDSP with JRiver.

MGBert approach is rather unique. Reading MGBert's original post, I suspect he did not get the full effect of crosstalk cancellation with the barrier due to the speakers spread or angle.

It is very important that the speakers should be around 20 degrees for the Ambiophonics to be successful. Even at 30 degrees the effect would not be good enough.

In MGBert's method, what is the recommended speakers angle?

Thank you.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 2, 2017 at 19:15:45
Satie
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I didn't give up on the barrier just that I did not get to that stage of experimentation yet after having moved to the short wall for wall loading positioning schemes and Limage type setups along with moving to time aligned 3rd order LP crossovers in the reverse split setup. I guess I can just put up the boards and see what happens though nothing is really completely optimized .

On the long wall placements I settled down with 1st order equidistant and used a pair of barriers like yours but flush to the front of the MT panel. That is where the observation came from about the opposing sidewall.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 04:56:01
josh358
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I don't think he said but according to the dimension on the diagram, the adjacent should be roughly 68" and the opposite 35", so that would be about +/- 27 degrees or basically the standard Blumlein equilateral triangle.

I assume the reason you want them closer in an ambiophonic setup is the HRTF? This is a practical issue for me since I have a projector and can't put my speakers at the recommended angle.

Your system must sound pretty spectacular, what with the Sound Labs and ther controlled directivity! I tried some of the sample recordings on the ambiophonics site last night with the backwave barriers in place and was surprised that I got a lot of the effect since I was listening at +/- 30 degrees. Not a 180 degree spread, but definitely outside the speakers and the sense of three dimensionality that I've heard from ambiophonics in the past, with sounds vastly in the distance or right up to the speakers depending. It was rough -- occasional buzzing and a hole in the middle -- but it was impressive nonetheless, particularly since my earlier ambio experiments with Maggies have failed.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 05:10:59
josh358
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Well I tried the RFZ barrier again last night with the boards somewhat further back and the results were at least as spectacular. I'm beginning to think that more is going on here than the M-T first reflection, I think it's blocking the higher frequencies from the woofers (lower will just go through and around) so that essentially I'm hearing only their first reflections. But whatever happens and it will be a few days before I finish rebuilding my computer and can look at the impulse response it's basically large room performance in a small one with the kind of lateral and z-axis localization I'm after.

Before that, I'd tried the ambio barrier again, this time from MGBert's recommended listening distance, but again with only partial effect. I'm not sure how much of that has to do with diffraction but some of it is just that I didn't have time to change the baseline after I moved closer so I was getting a hole in the middle at that distance.

I ended up listening to the sample files on the ambiophonics site with the barriers still in the RFZ position. As I said to stchelvam, the effect was rough because the speakers were at the wrong angle but I was nevertheless impressed -- there was an awesome immediacy to the sound that reminded me of a binaural recording, or the front part of one anyway.

This stuff -- nulling room acoustics and crosstalk cancellation -- really takes things to a different level.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 11:48:57
MG-bert
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From Josh358: "This stuff -- nulling room acoustics and crosstalk cancellation -- really takes things to a different level."

And that, sir, was the drum I was beating when I was posting about this a few years back. It really dwarfs the improvements you get from fancy cables or amps. In fact, it's worth just getting long lengths of plain zip cord to use as speaker cable until you get placement nailed.

And yes, the MMGs are probably better candidates since, according to Floyd Toole's book "Sound Reproduction: Loudspeakers and Rooms" which has an entire section (9.1.3) which he calls "An Important One Toothed Comb - A Fundamental Flaw in Stereo" which relates to the crosstalk phenomenon, the critical frequency is about 1,300 Hz. So the MMG tweeter is definitely in play there. The link to the Toole book I posted earlier seems to no longer include that section; pity.


Of course, it also has zero WAF. ;-)

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 12:28:17
josh358
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Fortunately I have Toole's book so I'd already read the chapter. I'd recommend that anyone curious or even not curious get a copy, it's well worth it.

I tried more ambiophonics experiments this morning, this time with the recommended 20 degree angle, but couldn't get it to work very well -- the same experience I had with the MMG's. Perhaps the side-by-side arrangement of the midrange and tweeter interferes with the timing of the crosstalk cancellation? I could hear decent spread beyond the speakers but it was no wider and probably narrower than the usual image with the speakers at 60 degrees. It just didn't match the true ambio barrier. That was just plain right, and if I could get my speakers to do that without pink styrofoam touching my nose my life would be complete.

I take it you're still using your original setup at home?

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 13:09:32
Satie
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I think you are right about the driver differences in lateral placement f'ing up the crosstalk cancellation from working. When we first talked about it here a decade ago I was thinking of how polk did its SDS processing, which I heard, and figured that if you did that electronically it would not work with laterally splayed drivers covering the critical frequencies. I didn't say anything since I didn't want to work out the physics explicitly, I just didn't expect it to work unless the mids were left to cover the critical frequency range in its entirety. Something you can do with the Neo8.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 3, 2017 at 13:18:02
josh358
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You could also do it by biamping and using separate parameters for the midrange and tweeter. I believe ambiophonics software usually allows you to split frequency ranges, in fact, I recall reading that the optimal angular location for the woofer and tweeter are different.

Another issue that occurs to me is that the test recording would have been made with an inverse square point source in mind rather than a 1/D line source. Again, the software would allow adjustment.

That said I've had some very interesting results with the speakers in their normal position. I'd be playing more with it now if I hadn't just learned that Amazon has delayed the deliver of my new table . . .

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 4, 2017 at 01:51:36
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Sorry for the delay. I am still unsure how to navigate here.

If you are using a barrier than the ideal separation should be around 10 degrees. Like in the picture below. It must not be more than 30 degrees. Unfortunately this is not practical to most.

The ambiophonics prepossessed files in the website can be listened without the barrier. That's how it should be listened. If you add the barrier than the cancellation signals would not reach you other ears and that explains the lack of soundstage.

Try again without the barrier. Alternatively, you can use any stereo recording and use it with a barrier. It requires no preprocessing or DSP. If you are using the ambiophonics plugins than do not use the barrier.

My main speakers are about one foot apart. There are no barriers. I use AmbiophonicsDSP with JRiver. I also use additional speakers for convolution. Basically, total speakers in my system are 26 units. Except for the main speakers, the rest are low priced small/micro home theater speakers.

IMO, even with the standard 2 speakers they sound so much better than stereo.


 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 4, 2017 at 06:42:20
josh358
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Hi STC,

Sorry if I wasn't clear but I listened to the preprocessed files without the barrier -- I used the barrier to listen only to unprocessed files. The barrier worked brilliantly even though the speakers were at the standard 60 degree angle, but I couldn't get the preprocessed files to work very well even though I tried the panels at the recommended angles and tried listening at various distances. I did get a spread beyond the speakers when I was in the sweet range, but it was actually less of a spread than what I get with the speakers at 60 degrees and no crosstalk cancellation.

I have Tympani IVA's in split configuration so the woofer panels are separate, and timed differently. However, the crossover from woofer to mid-tweeter panels is 300 Hz third order and as I understand it in the RACE algorithm the bass below 400 Hz bypasses the crosstalk cancellation. The separate panels also didn't have a deleterious effect when I used the barrier.

Maybe I should try the panels even closer together? I thought I had them at about 20 degrees or less. As others have mentioned, though, the Maggies have side-by-side mids and tweeters whereas you're using the crossoverless Soundlabs and I'm thinking that the lateral displacement of the drivers may be interfering with the crosstalk cancellation since the acoustic centers are laterally displaced by about 5":



Also am I correct that the greatest effect of the XTC is at about 1 kHz? In which case maybe I should optimize the distance for the midrange units -- will try it again using that as a parameter. Meanwhile, I ordered a copy of AmbiophonicDSP to play with.

I'm impressed that you're doing convolution! I'd love to do that but I didn't see a way to make it practical. Don't the inexpensive home theater speakers reduce the quality of the sound? I assume you got the impulse responses from the source mentioned on the Ambiophonics site, but I'm curious about what you used for amplification and DA conversion and what you're using for the convolution -- will JRiver handle that many channels? Have you written this up somewhere? I'm intensely curious -- it's something I'd love to do.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 4, 2017 at 07:15:16
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You raised an interesting point. Will forward your query to Ambiophonics founder, Mr. Glasgal. You can also email him at glasgal at ambiophonics.org.

Meanwhile, about the my convolution setup, it was a simpler version with one IR only. I would do another two or three IR in the future but frankly, this is already very good considering my room size. You just need to be creative. I also think the convolution would work with stereo setup as well.

The small HT speakers output are low and ithey don't affect the SQ. I have the actual recording of 2L Magnificat where you can compare the original and Ambio with 12 speakers. I used Roland CS10EM binaural microphone. Unfortunately, I couldn't insert the SoundCloud link with my phone. The sample is also available in my profile page.

I will try to put in the link tomorrow. It is way past bed time ....:)

ST

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 4, 2017 at 09:54:10
MG-bert
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Josh358: "I take it you're still using your original setup at home?"

Short answer is yes, unfortunately I don't get to listen to it as often as I'd like.

Longer answer: I have tried to do the setup shown by st.chelvam, and got pretty good results. I used my 2 FRT panels as the barrier, stiffeners touching so the total barrier was about 4" wide, and using those foam pipe insulators on the forward edge as a headrest. I had my Gunned MMGs touching the FRT panels, about 4 feet away from my ears. So the angle between the tweeters was between 10-20 degrees, which should be ideal. I was thinking, though, that the fact that the FRTs are wooden panels did the configuration a disservice, since the high frequencies bouncing off the hard surface might have had a smearing effect. So I have a plan to glue some insulation to that reflective surface (thinking the textured foam used as mattress cushions) to reduce those reflections. These reflections don't seem to be a problem with the separated configuration I wrote about initially, btw. Haven't had the opportunity to do that yet.

And besides, the separated configuration allows for a TV screen so I can control the music selection or watch a concert video. Can't do that with the barrier dead center. Although a VR reality set of goggles would make that possible... ;-)

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 4, 2017 at 14:03:00
josh358
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Yes, the ambio barrier articles I've seen all mentioned absorption. But since it isn't practical and I was able to hear the effect with just those slabs of pink styrofoam I'm not going to try it.

Need something more practical! I'll give your barrier setup a more careful try, and also try the RACE setup again, although I'm stymied because even if I can get the Maggies to work I have the same problem you have -- I need to put a screen between the speakers. In a perfect world, I'd have a huge room and a motorized acoustically transparent screen, but realistically, the only way I can think of to do this would be to push the speakers together for music listening and use the laptop rather than the projector.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 5, 2017 at 18:57:10
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>>Also am I correct that the greatest effect of the XTC is at about 1 kHz? In which case maybe I should optimize the distance for the midrange units -- will try it again using that as a parameter. Meanwhile, I ordered a copy of AmbiophonicDSP to play with.


I forgot to address this point earlier. The barriers will do the isolation from above 1000Hz. However, the separation gradually declines from 1000Hz to 400Hz. it was mentioned in the many AES papers that you will find on the website.

Just a word of caution here. Ideally, the main speakers should be line array type. So it is possible that you are right.

I hope you get your AmbiophonicsDSP working well. Please note that the values would change if the sampling rate of the source changes. Initially, it would be tter to experiment with big ensemble classical music and only then move to other genres. The "zentrum" should be set around 2 to 3dB. With convolution speakers, I set the "space" to zero. However, your mileage may vary and set them according to your taste for non convolution approach.

And lastly, here is the link which was made earlier with 8 convolution speakers.

It is difficult to evaluate the sample as my stereo and Ambio with 12 speakers were recorded with binaural microphone and meant to be heard with headphones. The original file is inserted between for you to compare all three versions.I could have done better with the stereo recordings but it wasn't easy to move the speakers. :)



 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 5, 2017 at 20:10:27
josh358
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"Just a word of caution here. Ideally, the main speakers should be line array type. So it is possible that you are right."

I think I may have made a mistake by using the central axis as a guideline. At 3 kHz, a wavelength is only about 4", so relative phase loses significance. There would still be an intensity difference that in theory needs crosstalk cancellation, but I don't think it can really be done effectively at that frequency since even a 2" head shift will change the effect from cancellation to reinforcement. So I plan to try again with the midrange as the baseline, and also with the software although I'm currently building a new HTPC so it will be a few days before I can try that.

Wow, huge difference in the sample! I'm just listening on cheap earbuds now, I'll head upstairs at some point tomorrow and find my Etymotics. But it's obvious even with the cheap earbuds. No wonder you're enthusiastic. How have you positioned the convolution speakers?

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 6, 2017 at 12:05:06
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It is great that some many here are experimenting with Ambiophonic methodologies. There are of course, papers tutorials, pictures, apps, a book, and components archived on the Ambiophonics.org website. It took me some twenty years to replace the barrier with software that did the same thing but better. In general crosstalk does not effect localization below 90 Hz or above about 4000 Hz. Unfortunately unless a barrier is absorbent and very thick it does not do a very good job below say 500 Hz, but still better than conventional stereo.

Any one of the new digital DSP gizmos, based on the RACE algorithm, works with almost any speaker type and with angles from about half the stereo speaker angle to say ten degrees. There are two easily adjusted parameters to accommodate any reasonable speaker angle. If the speaker angle is too narrow it is hard to stay on the center line between them but it will work. If the angle is too wide you begin to get a head shadow and a pinna error but compared to such errors in stereo this is not serious. Lots of other psychoacoustic points on the website or ask me about Envelophonics and 3D surround. Ralph

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 7, 2017 at 16:49:33
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"How have you positioned the convolution speakers?"

It is recommended by Ralph that the rear half of the side wall to be given priority and followed by the rear and front half.The recommendation was based on numerous research.

Since I am limited to only one IR, I placed mine at 90 to 130 degrees, covering the rear half. I use St.Cecilia concert hall's IR for 45 degrees. With my current speakers arrangement this yields a better integration over the 60 degrees IR. Over this weekend, I will be trying 90 degrees IR and see if it improves further.

While the proper way is to use all 25 IR of St.Cecilia or any other IR by placing the speakers at the actual measured location, I opted to recreate my own "wall" due to space and lack of technical knowledge for pro sound implementation.

It is addictive as playing around with the convolution creates the very best listening experience. The method works for stereo setup too.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 7, 2017 at 18:36:56
josh358
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Thanks, I was reading up on inexpensive speakers. It looks like there are some decent ones though hard to know what would work. But man, once you add all those DAC racks and amplification it wouldn't be cheap! Also, I'm not sure how I'd feed the DAW with my usual source, JRiver -- haven't looked into it but I wonder whether you'd need to run two machines.

OTOH, no reason I can't do what you did and try a simpler setup. I have some Monsoon computer speakers and I could use the motherboard audio to experiment, with the impulse response in JRiver . . .

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 7, 2017 at 18:59:58
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Josh,

You need not spend a fortune on the small speakers. Mine are a mix of Yamaha, Panasonics and Sony. Speakers the size of a CD (see picture). The role of the convolution speakers is to act as sound bouncing off the wall and therefore the quality, in a small room, doesnt matter. Moreover, the I use JRiver's PEQ to cut all frequencies below 200Hz and above 4500Hz.

Basically, you only need one amplifier. I was driving 4 speakers with one amplifier. Now, I am driving all 22 speakers with just 3 amplifiers. You can drive all speakers with one 100Watt Amp or better still get a Behringer or Crown to drive all the speakers as the output volume is very low.

I am using the http://www.gearbest.com/speakers/pp_39924.html amp to drive the other 8 speakers. You would probably need less than 10 Watt for all the speakers. You can see the diagram in my profile page. My total budget for all the speakers and amplifiers is below US$200 as the HT speakers were bought used.

ST

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 8, 2017 at 05:21:42
josh358
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Thanks, Ralph. I'll give RACE another try, taking into account what you've said here. My main problem is that my system does double duty for home theater so in the absence of an acoustically-transparent screen and a short-throw projector, I don't see how I could reduce the stereo angle much below 60 degrees, and I don't have $50,000 for BAACH. (Really, I don't begrudge them the selling price, but I don't see why there can't be an inexpensive software solution for head tracking.)

But I certainly want to give it a more serious try than I have in the past, with speakers at an optimal angle and careful adjustment of the parameters. And even if ambiophonics proves impractical for me because of the projection issue, I'm intrigued by the notion that you can do convolving reverb with inexpensive speakers -- I'd always thought that that would be impractically costly.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 8, 2017 at 05:32:40
josh358
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Wow, at that price, you can't afford not too!

I'm definitely going to try this once I get my new HTPC up -- I have the box built, but the monitor I was planning to get is backordered so right now I'm scrambling for a substitute.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 8, 2017 at 07:39:10
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I have similar problems with screens and projectors. But by raising the screen I have gotten the speakers in front of it without difficulty and you never need a center speaker with Ambiophonics. Also using two speakers with RACE behind the viewing position I have a full circle of direct sound from 5.1 media with just four speakers. I also have one system where the speakers are behind the screen somewhat. It works just fine. Ralph

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 8, 2017 at 17:01:33
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You can also use acoustically transparent screen fabric for the screen so that the speakers go behind the screen.

ST

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 8, 2017 at 18:37:34
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" So the angle between the tweeters was between 10-20 degrees, which should be ideal."

The crosstalk effect only effective for frequencies below 4000Hz. You may get a better result with the midrange separated by 10 to 20 degrees.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 07:11:34
MG-bert
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STC: "The crosstalk effect only effective for frequencies below 4000Hz. You may get a better result with the midrange separated by 10 to 20 degrees."

The crossover of my MMG speaker is actually at 1,000 Hz, so the tweeter is handling those frequencies. Working out the geometry I used when I had the speakers as close together as the 4 inch wide barrier would allow, the included angle between tweeter quasi-ribbon centers was 16.6 degrees, and between woofer panel centers was 23.5 degrees. Actually a bit less because I had rotated the panels a bit to reduce phase differences between the woofer and tweeter at the listening seat.

I agree; if I sat further away from the speakers (I actually had my forehead up against the panels I used as the ambio barrier) the results may well be better, especially since the high frequency "smearing" should be directed more away from the ears. I will try that later; too much going on now to devote time to reconfiguring the system.

Which angle should govern: if getting the woofers within a 20 degree included angle means the tweeters are closer than 10 degrees included angle, is that worse than the tweeters being right at 10 degrees but the woofers being greater than 20 degrees? I just had a thought of a new barrier configuration to try, with my 2 FRT style panels touching each other in the plane of the MMG speakers and spreading out to 4" to 6" wide closer to the listener. In other words, a wedge-shaped barrier vice a standard rectangular barrier geometry, as seen from above. That SHOULD direct any smearing early reflections from the FRT panel surfaces further still from the listener. Also, that would allow me to bring the MMGs even closer together; hence the angle questions. Thank you for your interest and assistance.

MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 15:00:53
josh358
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Thanks, Ralph. Unfortunately I have Maggies so can't put them below the screen, or behind it. So I'll give it a try this week but the only way I could do this is to move them when I'm listening to music -- which actually isn't out of the question.

I'm also sorely constrained on what I can fit behind my head -- my room is only 14' deep so I have to sit close to the rear wall. I was wondering whether a nearfield monitor would work for the rear.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 15:02:54
josh358
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If I'd been planning this from the beginning, I would gone with an acoustically transparent screen and a short-throw projector. At least I think I would have -- that might actually put the screen too close for comfort, since the Maggies have to be something like 5' out from the wall and my room is too small.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 17:59:48
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"...Maggies have to be something like 5' out from the wall and my room is too small"

I see the difficulties. My room too is small. Used a lot of rockwool at the back and side to damp the speakers so that I could move much closer than the recommended distance.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 18:10:28
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MG-bert wrote "Which angle should govern: if getting the woofers within a 20 degree included angle means the tweeters are closer than 10 degrees included angle, is that worse than the tweeters being right at 10 degrees but the woofers being greater than 20 degrees?"

I see your point. I guess you can only tell which is correct by experimenting.

Thank you for sharing your setup.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 9, 2017 at 18:23:13
josh358
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I was thinking about that. You don't really need the backwave if you're adding convolved reverb, in fact, you're better off without it. But I'm not sure how close you can get to the wall without impairing the sound. In any case, it's still kind of moot because I don't have an AT screen.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 10, 2017 at 06:40:41
Posts: 6
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Thanks for not giving up. The rear speakers can be in the near field. I have one pair that is only about two feet away. Just adjust the rear level so you don't have frontal sound seeming to come from the rear. You can also delay them if you have a control but that is seldom necessary. The rears do have to be RACE or similar crosstalk cancelled and at a narrow angle or you will localize to them.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 11, 2017 at 13:56:25
josh358
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Thanks, that's good to know. Two feet I can handle!

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 13, 2017 at 09:25:53
MG-bert
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Ralph:

I've been meaning to comment on what appears to be an error (typo?) in your free on-line Ambio book. In Chapter 8, there is a section on Ambiodipoles which features an equation for determining how far one can sit away from a central barrier per the 1986 AES paper by Timothy Bock and Don Keele Jr. I remember finding an error in their resulting equation; there definitely is in the equation you state, namely L=X(H+T)­D.

My derivation, using all the terms as defined in your Ambio book, is

L = X(H+T)/(D-T)

If you need it, I could send you my derivation. BTW, I'm a structural engineer, so this kind of geometric exercise is part of my professional skill set.

­
MG-bert

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 13, 2017 at 14:00:45
Posts: 6
Location: New York City
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Thanks. Right you are. The D should be in the denominator. Somehow when the book was added to the website, the slash got lost. I don't doubt the equation can be improved. For instance if D is very small so that the speaker separation is about twice T, the thickness of the panel, and if the panel thickness is about the width of the head H then the good listening distance to the edge of the panel is close to HX/D.

Now for some realism, if the speakers are close together at two feet and the barrier is say six feet long for a ratio of about 3 this implies that one can listen at the edge of a head width barrier up to 6 head widths away from the edge or 3.5 feet or over a meter away. In practice this does not work. As soon as the left eye can see the right speaker, and the right eye can see the left speaker you get mono. Ralph

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 20, 2017 at 03:38:55
motberg
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Hi, thanks to all participating and posting about these ideas.

I just setup something like a full barrier made out of 2 sheets of 50mm acoustic foam. These are at an angle to accommodate going around my equipment which is in the center of the speakers (so the barrier touches the side of each of the speaker cabinet and there is some dead space between the foam... the last 70CM to the LP is pretty much a solid block 100mm thick). I have the current total angle at about 40 degrees, sitting somewhat nearfield about 2 meters away from the speakers. My speakers are typical box monitors, but use a single Heil from about 800 hz on up and a long throw woofer for below that..

I think in reality the effect works well (almost 100%) while sitting up to 15 CM from the barrier edge in the way I have it set up currently.

This worked as I expected for sound stage, as I have a couple Carver C-9's and a C-16 currently in the closet and in the past used a C-1 with Carver Amazings -- but I was totally surprised by the increase in clarity using the barrier.. top to bottom everything was more precise... performed like a serious upgrading to the speakers...

So I was wondering if any software version can match the physical barrier as far as this increase in clarity is concerned. I already purchased Amtra, but my preliminary tests have not been successful.

I am sourcing materials for a more permanent style barrier. I will also give another try to the software again (at 20 degrees) when I tear down this temporary barrier, but I would be interested to know if in fact the software can duplicate the clarity improvement as well as a correctly devised physical barrier.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 20, 2017 at 11:09:10
Posts: 6
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Thanks for being adventurous enough to try Ambiophonics. In general software outperforms a barrier in practice. This is because the barrier does not work over as wide a frequency range as the software and normally barriers cannot cancel crosstalk as completely due to diffraction at the edge. It is also hard to keep one's head close to the end of the barrier or watch a 3D movie.

It is essential with software that the speakers be less than a third the stereo spacing. This is to avoid introducing a head shadow that the software is not anticipating and also to keep the pinna direction finding errors to a minimum.

If Amtra is not your cup of tea, try the little miniambio component and then you don't need a computer running all the time. It also has a parametric equalizer that you can use to make things sound like the barrier if you do hear a difference. (Remember that stereo is quite colored With any of the RACE devices, I get a really wide, up to 180 degree stage, with many LPs or CDs not to mention movies like Avatar. Don't give up. Once you have it working you will never want to listen in 60 degree stereo again.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 20, 2017 at 20:07:06
motberg
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Hi and thanks for the additional information.

I still have a miniAmbio box I bought a couple years ago, but I found the ADC/DAC converters too coarse for entry into my systems signal path.

I replaced the old miniDSP units I am using for sub and super-tweeter control with the new miniDSP 2x4 HD unit - and I thought that was a big upgrade for sound quality. So I think it would be a fantastic thing if someone can port the RACE stuff to the new miniDSP 2x4 HD, which would offer more processing power, better ADDA, and direct digital input which can eliminate the AD step.

Or better yet, some box which would offer hi-res digital input and output.

I need travel for work the next few weeks, but will try some of the other RACE plugins and programs as soon as I return. My system is in a dedicated small treated room, music only, with a pretty good computer-based front end (listed in my HeadFi profile), so I am pretty confident I can get this to work one way or another..

Thanks again...

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 21, 2017 at 09:21:51
Posts: 6
Location: New York City
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I will forward your suggestion to the DSP4you management. I too think the Ambiophonics plugin should go into the 2x4 HD unit and told them that almost a year ago. But I guess the demand is not there yet.

I have never noticed any coarseness with the analog miniDSP and they have sold hundreds of them. It operates at 96/24 so I don't see why there should be a problem. But I agree a digital input and output for that matter would be nice. I use only digital amplifiers from TACT and NuForce so I am normally 100% digital up to the speaker leads. But I use miniDSPs for demonstrations, 3D movies, etc. and have had no problems.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 22, 2017 at 05:03:36
Posts: 12
Joined: March 2, 2017
You can always port in ambiophonics to your MiniDSP the DSP is available for $10/- from the MiniDSP site.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 22, 2017 at 17:51:51
Posts: 12
Joined: March 2, 2017
"I too think the Ambiophonics plugin should go into the 2x4 HD unit and told them that almost a year ago. But I guess the demand is not there yet."

It does. The plugin is available for 2 x 4.

 

RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics, posted on March 23, 2017 at 07:16:17
motberg
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Hi and thanks again for the additional comments.

I removed the barrier and set the speakers at 20 (10/10) degrees and tested Amtra again (exported processed files in the default settings and used in my normal setup) and found some artifacts with pop music type productions (classical was better but not as clear as without the processing). However, I immediately noticed some of the possible benefits of the speakers in this configuration, so will keep the speakers set at 20 degrees until I return from the business trip.

I did a quick check at miniDSP for the software and iirc they specifically mention it will not work with the HD version miniDSP... I do not know how difficult to do this port, but with the proliferation of desktop speaker setups currently being used, I would think there is some marketability in a higher range product than the current. I admit that my initial observation of grainy-ness with the standard miniDSP may have been partly or wholly attributable to some cognitive bias on my part (my DAC is a well-fed Audio-GD NOS7).

Anyway - I am currently building a second input to my preamp for casual listening. This will be a SoTM SMS-200 to some yet-undecided DAC but with a new computer. I will build his computer with the idea to be able to run either Samplitude or JRiver with an Ambio VST plugin. I already have all the software, and some of the computer parts, so hopefully in a month or so I will be able to do a proper test.

For anyone interested in this stuff, I have just learned of some software seeming aimed mostly at pro-level use (meaning probably very expensive).. but nonetheless interesting in that this company also found the concept worth developing into a professional level product.
https://www.theoretica.us/bacch-dsp/

 

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