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In Reply to: RE: Another First Reflection Trap (FRT) Adventure : Quasi-Ambiophonics posted by MG-bert on October 05, 2013 at 09:06:54
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
Follow Ups:
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.
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.
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...
You can always port in ambiophonics to your MiniDSP the DSP is available for $10/- from the MiniDSP site.
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.
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/
"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.
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
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
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.
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
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.
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.
Thanks, that's good to know. Two feet I can handle!
You can also use acoustically transparent screen fabric for the screen so that the speakers go behind the screen.
ST
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.
"...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.
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.
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