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Diffusison

68.6.217.177

Posted on September 7, 2016 at 21:24:41

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

Any ideas about rear wave diffusion for panels?
Keeping in mind that size goes up as frequency DROPS, how low would you think I need to go?
How much of the rear should be effected? \
Would a 24" x 24" diffusor per panel suffice? Larger?
Any preferenes as to TYPE of diffusor to purchase or construct?

My panels are about 34" from the wall which is TOO CLOSE and I think I could open up the sound stage AND improve imaging at one stroke. Would you say this is an accurate guess?

Too much is never enough

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stustan

09:25:09 09/22/16

play-mate

02:16:56 09/21/16

josh358

16:43:37 09/28/16

...

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stustan

09:25:09 09/22/16

play-mate

02:16:56 09/21/16

josh358

16:43:37 09/28/16

play-mate

19:01:59 09/28/16

josh358

07:09:22 10/02/16

play-mate

10:02:25 10/02/16

josh358

19:14:55 10/02/16

Satie

09:54:01 10/03/16

pictureguy

11:26:40 10/06/16

Satie

14:26:37 10/06/16

pictureguy

15:47:20 10/06/16

Satie

18:54:53 10/06/16

josh358

10:02:43 10/03/16

play-mate

00:15:45 10/03/16

josh358

04:31:53 10/03/16

bwaslo

18:06:52 09/23/16

josh358

18:20:44 09/22/16

pictureguy

11:10:40 09/21/16

Satie

12:46:44 09/22/16

pictureguy

15:28:46 09/22/16

Satie

12:42:07 09/23/16

pictureguy

13:21:13 09/23/16

Satie

13:31:46 09/23/16

bwaslo

20:36:49 09/20/16

pictureguy

00:09:51 09/23/16

Have you seen GIK's new diffusers?

johnvb

19:02:36 09/12/16

RE: Have you seen GIK's new diffusers?

pictureguy

11:11:23 09/22/16

RE: Have you seen GIK's new diffusers?

johnvb

16:13:45 09/22/16

RE: Have you seen GIK's new diffusers?

pictureguy

16:36:08 09/22/16

RE: Have you seen GIK's new diffusers?

johnvb

17:08:27 09/22/16

RE: Have you seen GIK's new diffusers?

Satie

11:21:56 09/13/16

RE: Have you seen GIK's new diffusers?

johnvb

05:47:15 09/14/16

BigguyinATL

14:30:09 09/08/16

pictureguy

16:58:26 09/08/16

BigguyinATL

10:44:49 09/09/16

pictureguy

11:37:48 09/09/16

Satie

09:58:08 09/08/16

pictureguy

10:21:30 09/08/16

Satie

10:35:03 09/08/16

pictureguy

12:26:55 09/08/16

grantv

12:50:29 09/08/16

RE: Wood works...

pictureguy

13:40:34 09/08/16

RE: Bamboo works, too :-)) ...

andyr

19:30:20 09/08/16

RE: Bamboo works, too :-)) ...

pictureguy

20:21:48 09/08/16

RE: Bamboo works, too :-)) ...

Satie

16:58:50 09/09/16

RE: Yes, I was, Satie. But ...

andyr

18:57:45 09/11/16

Nominal 2 x 2's, yes

grantv

14:13:00 09/08/16

RE: Nominal 2 x 2's, yes

pictureguy

16:40:45 09/08/16

RE: Diffusison, posted on September 8, 2016 at 09:58:08
Satie Audiophile Posts: 5426 Joined: July 6, 2002	I think you want the diffusors longer to cover 4 ft of the center backwave output

RE: Diffusison, posted on September 8, 2016 at 10:21:30
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	Is that HIGH or WIDE? or do you mean 16 sq feet PER SIDE = 4' x 4'? I'm afraid I simply do NOT have that kind of space, especially on the RH side. The LH Side? I MIGHT be able to make it work. If it makes a difference? I have 1.6s Too much is never enough

RE: Diffusison, posted on September 8, 2016 at 10:35:03
Satie Audiophile Posts: 5426 Joined: July 6, 2002	High - to match the length of the drivers. I would not expand to 4 ft wide before knowing that 2 ft wide is insufficient. It likely is enough.

RE: Diffusison, posted on September 8, 2016 at 12:26:55

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

I think I can manage 4'H x 2'W Diffusors are a max of 7 1/2" thick and than only in a few places.

Each panel has an amp on a stand behind it. So I'm 'space constrained'.

Link is to an image / price. Price is ridiculous. I can build the same thing for a fraction this ask and from a BETTER material.
Too much is never enough

https://www.bhphotovideo.com/bnh/controller/home?O=&sku=4376

Wood works..., posted on September 8, 2016 at 12:50:29
grantv Manufacturer Posts: 7727 Location: B.C. Joined: January 15, 2002	I built mine from 2 x 2's, IIRC also right around 7 1/2" deep.

RE: Wood works..., posted on September 8, 2016 at 13:40:34

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

Of course wood works. But WHERE do you get 2" x 2" wood?
All the 2x2 I see is REALLY 1 1/2" and NOT suitable for this use. If I had a MAJOR wood shop with a Planer and a GOOD table saw, I could work with non-dimensional lumber.
After all, a quick count shows 144 cells arranged in a 12x12 matrix.

Besides, wood weighs a LOT. Yellow Poplar, for example, runs nearly 28lb per Cubic Foot. I've calculated a need for about 1.25 cubic feet which would go 35lb. Ridiculous waste of wood, IMO, and difficult to hang. And you can't actually GET 2" x 2" wood!

I can make what you have, painted ANY COLOR you wish and bring it in for about 5 POUNDS, with backer, paint and hanging hardware.

I won't disclose, at this time, my choice of material, until I've MADE some. It isn't impossible, but it is somewhat a PIA to get what I want, since NOBODY carries it, especially the 'home stores' .
HINT: Not a hard foam OR castable foam.

Too much is never enough

Nominal 2 x 2's, yes, posted on September 8, 2016 at 14:13:00
grantv Manufacturer Posts: 7727 Location: B.C. Joined: January 15, 2002	I used 2 x 2's, yes = 1 1/2" x 1 1/2" Worked fine for my room, perhaps not ideal for you. The weight is minimal, not a waste of wood IMO (but then I live in BC Canada, wood is our "thing"), easy to hang. It was a fun project to boot... Have fun with your project.

Two kinds:, posted on September 8, 2016 at 14:30:09

BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002

A polynomial Diffuser (see picture) is limited in frequency buy its depth and actually profides a lot of attenuation as well (no necessarily good - but it could be) the evective frequency the the 1/4 wave defined by the differences in the depth of the difusor components eg. 3" difference works at 1kHz and up. A wedge or tube diffusor is also determined by its size. By angling a dipole speaker the extension down to lower frequencies can be enhanced. I use a 45 degree toe in on my planars that essentially fire into the rooms corners (one corner has an equipment rack and the other a software rack).

24" x 24" is too small consider twice or three times that. 24 x 72 is a typical side wall diffusor I use for non-dipoles baffled speakers. 36" by 72" for a front wall diffusor behind each speaker.

"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

RE: Nominal 2 x 2's, yes, posted on September 8, 2016 at 16:40:45
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	I'd think about 2x2 IF I could find a way to calculate a 16x16 matrix. That's 24" worth of '2x2'. Too much is never enough

RE: Two kinds:, posted on September 8, 2016 at 16:58:26
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	Polynomial is a new term to me. Though I KNOW it is a math term. What I want to build LOOKS similar (but not exactly) and is called a 2D QRD. I would think that as you DIFFUSE the back wave of the panel, you will also reduce its amplitude as you spread the SAME energy out over TIME. I'm ok with that. Too much is never enough

RE: Bamboo works, too :-)) ..., posted on September 8, 2016 at 19:30:20

andyr
Manufacturer

Posts: 12550
Location: Melbourne
Joined: September 2, 2000

I have the same problem - lovely wide soundstage but it lacks depth (compared to my last listening room. I suspect because, like yours, my panels are too close to the wall.

Sure there are many things you can use to diffuse the rear wave (and diffusion is what is required, IMO - not absorption). So what I am thinking of doing is creating a lattice out of 1"D bamboo poles and fixing this to the wall (which in my case is sloping :-(( ). It will run up to about 7' high and span to the outside of the panels - so about 10' wide.

The gaps between the lattice will be 1.5 - 2" square. If it delivers the soundstage depth I want ... then I can get the required WAF approval by painting the poles to match the walls.

Andy

RE: Bamboo works, too :-)) ..., posted on September 8, 2016 at 20:21:48

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

I have a COLLECTION of about a DOZEN Pool Noodles in 4" diameter. I tried making an 'array' in a PHi Shape 'arc' which is like a 'section' of snail shell. maybe 30 or 40 degrees or arc. I used PVC and ingenuity. PVC did NOT go up thru the center of the Noodles.
I'll revisit that LATER.

Another test would be using the famous 'Fake Fikus'. This would be expensive at the density needed AND take up lots of floor space. Nope, I'll try other stuff

A FLAT array of bamboo is NOT correct. That automatically limits frequency and 'regularizes' the dispersion pattern, and to only the horizontal plane AT THAT.
In short, presenting the panel with variable spacing and distance of elements of an otherwise regular array will provide a spread of frequency response. the pattern will remain horizontal.
Building to a 'rule' should facilitate that goal.

Too much is never enough

RE: Two kinds:, posted on September 9, 2016 at 10:44:49

BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002

more attenuation occurs with w QRD panel because of phase cancellation. one portion of the reflected wave becomes 90 or 180 degrees out of phase with reflecttion from other portions of a signal.

The Drawback of one of these "stepped" QRD like panels when used directly behind a planar dipole that is parallel to the diffuser is that specific integer frequencies get attenuated or theoretically reinforced while other frequencies do not.

In most installations the diffuser is not going to be back wave.

The cheapest way to make non QRD style geometric reflective diffusers to make are plywood or particle board boxes. Vinyl lovers use the crates or boxes behind the speaker or angled against the wall and stacked on each other to the desired height. You can also build some of the cubes as a boxes with a damped tuned port to be a home made "tube Trap" helmholz attenuator.

"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

RE: Two kinds:, posted on September 9, 2016 at 11:37:48

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

Fortunately, the panel and the diffuser are rarely parallel. In my case, they'd be offset by about 11 or 12 degrees. Panels are vertical.

The OTHER kind of diffuser I've seen is the 1D QRD, which is a big box with steps in calculated depths and all the same width. These can be pretty much as LONG (tall) as you wish. I don't have the facilities to construct these, since I'd need a good table saw and MUCH more construction space than currently available.

Calculators I've seen are 'seeded' with a Prime Number which may be key in avoiding 'cogging' frequencies.

How is a 2D QRD behind a panel any WORSE than the bare wall?
Too much is never enough

RE: Bamboo works, too :-)) ..., posted on September 9, 2016 at 16:58:50
Satie Audiophile Posts: 5426 Joined: July 6, 2002	I thought AndyR was going to do overlaid vertical and horizontal lattice. You are bringing up a good point though about wanting not to make the intervals too regular - perhaps use QRD tuning for each axis for width rather than depth.

RE: Yes, I was, Satie. But ..., posted on September 11, 2016 at 18:57:45
andyr Manufacturer Posts: 12550 Location: Melbourne Joined: September 2, 2000	I think it is a good suggestion of pictureguy's to make the spacings irregular. Andy

Have you seen GIK's new diffusers?, posted on September 12, 2016 at 19:02:36

johnvb
Audiophile

Posts: 495
Joined: October 26, 2011

Also I have found that the gearslutz studio/acoustic/building forum has a lot of great ideas for diffusers, like this one:

https://www.gearslutz.com/board/studio-building-acoustics/766977-diy-sound-diffusersa-free-blueprintsa-slim-optimized-diy-diffuser-designs-fractals.html

I no longer run Maggies, but still have my styrofoam QRDs on the front wall, so much lighter and easier to move than the wood versions (they are in frames, on wheels, in front of closet doors). Bought them from SRL acoustics.
http://www.srlacoustics.com/

http://www.gikacoustics.com/product/2a-alpha-panel-diffusor-

RE: Have you seen GIK's new diffusers?, posted on September 13, 2016 at 11:21:56
Satie Audiophile Posts: 5426 Joined: July 6, 2002	Well, that is a different way to get Freq specific slots for diffusion.

RE: Have you seen GIK's new diffusers?, posted on September 14, 2016 at 05:47:15

johnvb
Audiophile

Posts: 495
Joined: October 26, 2011

Yeah they kinda remind me of RPG'S BAD panel, which are not marketed as diffusers, but "sound absorption across the NRC frequency bands while preserving the ambiance of the space".

To the OP, I also experimented with polycylindrical diffusers when running Maggies, they worked great on the front wall. You do not get as much time delay diffusion with them, as with QRDs. But they need to be a good distance from the listener, in my smaller room they added too much reflection. They can be made easily as a temporary test, with 1/8" Masonite bent onto a wood frame (again see the Gearslutz forum).

Now I run all absorption, except the QRDs in the middle of the front wall.

RE: Diffusison, posted on September 20, 2016 at 20:36:49

bwaslo
Manufacturer

Posts: 245
Location: Portland, OR USA
Joined: September 10, 2006

If you want to make your own, I designed and simulated a version of a "step diffuser" with emphasis on easy and inexpensive to build. It performs very well and uses standard (in USA) firring strip lumber in as-bought lengths. It is even possible to make these without having a saw, if you can get a big-box store to make a few simple cuts for you.

See attached link url to get to it..
_

Make easy high performance diffusors:-->http://www.libinst.com/diffusers/Depot_Diffuser.html

Horn Design Spreadsheet:--> http://libinst.com/SynergyCalc/

SmallSyns:-->http://www.diyaudio.com/forums/multi-way/292379-s

Diffuser build thread at diyaudio

RE: Diffusison, posted on September 21, 2016 at 02:16:56

play-mate
Audiophile

Posts: 948
Joined: November 21, 2008

Hey Guys

Playing around with absorption and diffusion lately is (in case of dipole planars) quite a challenge, so as an immediate trial & error solution I came up with a cost effective way.
These are made of standard fibre glass roof panels with a stainless steel tube drawn trough.

Easily made and highly effective.

Be inspired.

Hysolid // Mytek Brooklyn // Spectron Musician III // Analysis Audio Omega

RE: Diffusison, posted on September 21, 2016 at 11:10:40
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	And they look to be bent to a VERY specific curve. Excellent use of materials, though. Very 'artsy'. Too bad I don't read GERMAN! Any idea how the builder drew the base curve? I'd use the SAME curve for a pool noodle diffuser I'm thinking about. I build a VERY unsatisfactory prototype before deciding that a phi-shaped arc would work better. …leo... Too much is never enough

RE: Diffusison, posted on September 22, 2016 at 09:25:09
stustan Audiophile Posts: 94 Location: Long Island, New York Joined: October 16, 2009	My wife and her sister stand behind my 1.7's during serious listening sessions. They are very similar in size (my wife and sister). My system sounds fantastic with live diffusion!!!

RE: Have you seen GIK's new diffusers?, posted on September 22, 2016 at 11:11:23

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

STyrofoam is fragile, in that it dents and WILL break.
My choice for a foam would be EPP foam which is flexible and will TEAR if provoked. EPP is also more chemical resistant than Styrofoam. EPP is available in 1.3# and 1.9# densities. I suspect you could make a fine 24"x24" QRD weiging less than 5 pounds, all-in.

I'll look up your link(s) and see what they have on offer.
Too much is never enough

RE: Diffusison, posted on September 22, 2016 at 12:46:44

Satie
Audiophile

Posts: 5426
Joined: July 6, 2002

Another diffuser you can build from styrofoam at a decent cost without the weight or difficulty of wood or skyline types.

http://arqen.com/acoustics/acoustic-diffusers/#thesis

RE: Diffusison, posted on September 22, 2016 at 15:28:46

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

Here's what I have in mind. NOT made from wood OR styrofoam.
A much better material exists at only 1.3# or 1.9# per cubic foot.

Too much is never enough

http://forum.studiotips.com/viewtopic.php?f=1&t=3327

RE: Have you seen GIK's new diffusers?, posted on September 22, 2016 at 16:13:45

johnvb
Audiophile

Posts: 495
Joined: October 26, 2011

Well I call it Styrofoam, in general terms, as opposed to wood. But the manufacturer says it's " high density polystyrene", and "high density EPS", so you can discuss with him what the specifics are.

I can tell you this. In order to fit and sink in the diffusers into the oak frames I built for mine, I had to flip over the diffusers and plane a good 1/4" off the backs. No unwanted damage what so ever.

One important point is these must be painted in order to achieve their full potential. They will absorb more than reflect when left unpainted.

See my post (reply 155) on this Audio Circle thread:
http://www.audiocircle.com/index.php?topic=116052.140

Also on the next page of that thread, the guy from SRL discusses his product.

http://www.srlacoustics.com/modular-2-foot-square-diffuser-q

RE: Have you seen GIK's new diffusers?, posted on September 22, 2016 at 16:36:08

pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008

EPP is Expanded Poly Propolene. It is VERY tough and will not crack like styrofoam or any of the styrene compounds.
Good luck SOURCING EPP, though. NO hobby shop will routinely carry it. They would ReSell far less since it is so darn DURABLE.
EPP is a closed cell foam and will take paint and is immune ot most solvents. I'll HOT GLUE it together when ready. I might not even use a BACKER which is an extra part NOT needed if I'm correct.
I can buy 24" x 48" sheets 2" thick which I can EASILY cut with an electric carving knife. I'm making the cutting jigs right now.

I think many would agree that WOOD is simply too heavy and ends up with both mounting problems and resource use justifications. Though I suspect, for the last, the synthetics are WORSE.

If you don't think EPP is 'special', check out the videos at Crash Test Hobby where a flying wing
is repeatedly flown INTO A BRICK WALL

I think the 1.3# per cubic foot stuff would work fine.
Too much is never enough

http://www.crashtesthobby.com/assassin-37-videos.html

RE: Have you seen GIK's new diffusers?, posted on September 22, 2016 at 17:08:27

johnvb
Audiophile

Posts: 495
Joined: October 26, 2011

LOL, awesome videos. If I had a nosy neighbor with one of those drones buzzing around my house, that Assassin would be perfect to "accidentally" take it out. :)

What design program are you going to use? QRDude is pretty popular:

QRDude

RE: Diffusison, posted on September 22, 2016 at 18:20:44
josh358 Industry Professional Posts: 12332 Joined: February 9, 2010	I love the look.

RE: Diffusison, posted on September 23, 2016 at 00:09:51
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	I have a 10" chop saw which will handle 2x6. That drops to 2x4 at a 45. Length is only limited by my industry and ability to do weird setups. Attached is a picture of the 30 cubic foot box I built to hold ALL my BBQ stuff, including 4x20lb bags of charcoal and all my extra ceramic pieces for indirect cooking. Pizza, anyone? Too much is never enough

RE: Diffusison, posted on September 23, 2016 at 12:42:07
Satie Audiophile Posts: 5426 Joined: July 6, 2002	So the foam PE does not need to be sealed like styrofoam to prevent unwanted absorption?

RE: Diffusison, posted on September 23, 2016 at 13:21:13
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	I really don't know. But I don't see the problem with a LITTLE absorption. And all it takes to seal ANY pores is a spray of paint. Too much is never enough

RE: Diffusison, posted on September 23, 2016 at 13:31:46
Satie Audiophile Posts: 5426 Joined: July 6, 2002	With standard styrofoam you do need to seal with paint to prevent significant absorption.

RE: Diffusison, posted on September 23, 2016 at 18:06:52

bwaslo
Manufacturer

Posts: 245
Location: Portland, OR USA
Joined: September 10, 2006

About the corrugated roofing diffusor -- I gotta admit, that's pretty clever. I wonder how well it models (or measures)?

Wish my trial month of AFMG REFLEX software hadn't expired.
_

Make easy high performance diffusors:-->http://www.libinst.com/diffusers/Depot_Diffuser.html

Horn Design Spreadsheet:--> http://libinst.com/SynergyCalc/

SmallSyns:-->http://www.diyaudio.com/forums/multi-way/292379-s

RE: Diffusison, posted on September 28, 2016 at 16:43:37
josh358 Industry Professional Posts: 12332 Joined: February 9, 2010	Great idea. I have to put a diffuser right where this window is and I hate to lose the view -- something like this might fit the bill.

RE: Diffusison, posted on September 28, 2016 at 19:01:59

play-mate
Audiophile

Posts: 948
Joined: November 21, 2008

Fellow Inmates

Proper room treatment should be on every audiophiles agenda. Big time.
The right balance between diffusion and damping of sound waves is especially important for our beloved dipole / planar technology, and I must admit, I have previously not given it so much attention that it deserves.

I have learned some good advice from different sources and people, but would put following link to your hearts & imagination :

http://www.hedbackdesignedacoustics.com/files/QuickSiteImages/AMS_for_Stereo_List._Rms.pdf

The cheap & easy bending of the translucent fibre glass diffusors, has enabled me to adjust angles and distances to the reflecting back wall and (sorry to say) adding another level of complexity in acoustical setup.
As the reflectors don´t suck up any excess lower frequencies, but rather disperse higher frequencies and break-up flatter echoes in midrange, there are further treatments to be made.

Tubed bass traps and a row of polystyrene bars across the ceiling, have made incredible progress in managing decay across different frequencies.

Not particular WAF friendly, but at least price sensitive.

regards Leif

Hysolid // Mytek Brooklyn // Spectron Musician III // Analysis Audio Omega

RE: Diffusison, posted on October 2, 2016 at 07:09:22

josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010

What do the polystyrene bars do?

I'm also thinking at this point of making a cylindrical diffuser to solve the window problem -- I have to put a diffuser right here:

Bending the acrylic would be a bit of a pain, though -- I'd need a form, felt, a heat gun, and a lot of luck! If I made the form with masonite I could make a catenary shape, which is supposedly better than a hemisphere in this application.

Some possible negatives: lobing between the two symmetrical diffusers, and the fact that hemispherical diffusers don't randomize phase (although their diffusion pattern is apparently much cleaner than that of a QRD or PRD).

What I really need is a wrecking ball so I can build a bigger room. :-)

RE: Diffusison, posted on October 2, 2016 at 10:02:25

play-mate
Audiophile

Posts: 948
Joined: November 21, 2008

Josh

Let´s face it - big planars in small rooms need HUGE efforts with damping & diffusion to reveal their sound potential. It is really better to size the planar to the room than opposite way around, but since we both have the circumstances, I will urge you to take 2 important steps :

First you need to get some massive absorbers that can catch the lower frequencies, cause they mock up big time. The simplest ( cheapest) way is to buy four packets of rock wool panels (at least 15 cubic feet) and cover them up in some cloth. This is much more effective dealing with low frequencies, than plastering lots of wall panels all over, because that will just kill the mid-high frequencies and leaving you an acoustical dead space.
Surely you should also get some curtains and a rug; - some plants and a book shelf would not hurt either.

Secondly some diffusion. Small spaces are easily problematic with flatter echoes & standing waves , which diffusors get rid of. A diffusor behind your listening position is also advisable.

While these measures are well known, I can only testify that it make a huge difference on planars.

The polystyrene bars are scattering sound waves near ceiling. Like diffusors they make the room seem acoustically larger and more spacious than it is.

I think it is better to trial/error some inexpensive efforts, than spending a fortune on the wrong things.

Planars do need reflections, so don´t kill the room with too much damping.

Kind regards

Hysolid // Mytek Brooklyn // Spectron Musician III // Analysis Audio Omega

RE: Diffusison, posted on October 2, 2016 at 19:14:55

josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010

Hey Play-Mate,

I'm still experimenting with speaker location so for now the room is basically bare. I expect I'll have a rug and whatever else I need to bring the reverb time down. Dust/allergies are an issue for me so I have to find stuff that's washable.

There's certainly room for some tube traps behind the woofers. Bass changes so radically with speaker position that I'm not sure what I'll need or where. Fortunately, the bass is surprisingly smooth given that the room is nearly square and it was awful when I had the speakers on the wall facing the fireplace. I think this is because the wall I'm against opens into a hall which breaks up the z-axis modes:

QRD diffusers behind the speakers definitely improved imaging when I tried them. I can't put a diffuser behind my head though since as you can see above I'm basically sitting within a foot or so of the wall. (Maybe a shallow cylindrical, which could also serve as a bass trap with some fiberglass behind it). I've seen absorption recommended for this situation and may give it a try.

The room features are apparently irregular enough to avoid obvious slap and flutter echo, even with only minimal furniture in it. The speakers snap into focus when I put the null at the first reflection points on the sidewalls, but to do that, I'll need to use the MiniDSP which I can't hook up until I lay in some more amps.

I'm fairly constrained in where I can put diffusers, sitting against the wall like that and with the hearth on the right and two windows and a column on my left. So still not sure how I'm going to work that out.

What amazes me though is how *good* things sound now without any treatment. A one note midbass resonance probably caused by the cavity to the left of the fireplace mantle goes away when the woofers are pulled forward as they are now, with the speakers equidistant as an experiment and a 6" gap between the mid-tweet and woofer panels (gap not shown in this shot -- also distances and angles are distorted by the panorama):

This arrangement is an experiment to get a sonic baseline, as a matter of practicality I'll go back to some variant of the split config. But the speakers are sounding great like this -- plenty of depth (they're at 5' off the front wall, would be even better at 6') and lateral spread -- the jaw-dropping "magic carpet" planar line source imaging that I love. Also, the IVA's are nicely balanced despite the lack of absorbent material -- a bit tipped up in the highs but not harsh -- whereas the MMG's sounded unpleasantly hot in this room when it was bare.

The big challenge for me right now is to get them sounding as good in split configuration as they do in line. Here, they're at the standard stereo spread but it's hard to do that with split config, so the image seems constrained laterally. And a radiator is in the way on the left, and the mantle on the right:

Anyway, as you can see, I have a lot of experimenting to do before I know where they'll be sitting -- I've only had them against this wall for a week or so. Once I know where they'll be living I'll start measuring and work on acoustic treatment. It may be that he only way to get them to image well will be to separate the midbass and low bass panels and move the low bass panels elsewhere, e.g., out in the hall. Which is why I'm intrigued by BDP's dipole woofer comparison experiment, in a room like thi sit really would be more practical to use just the M-T and midbass panels and use dipole woofers for the deep bass. But the bass on these speakers is so stunningly realistic that it's quite a challenge to equal it!

I've still never heard midbass to equal the Tympanis, that combination of planar bass clarity and near-dynamic slam. It's one of the things I love about them.

RE: Diffusison, posted on October 3, 2016 at 00:15:45

play-mate
Audiophile

Posts: 948
Joined: November 21, 2008

Dear josh358

I guess, this is a dedicated listening room and not your family living space. That should give you a little freedom to setup less conventional.
As the room is small, I think it would be wise to consider as much symmetry as you can and therefore using the fireplace as the back wall of the setup. That will, of course, interrupt the access to the room, but hey - it´s not easy to enter a Ferrari either.
As bass nodes are difficult to localise, traps are not critical to position. Maybe you could build a discrete triangular, wall mounted bass trap in the hallway.
An even sonic decay of a room, is the key to clarity in all frequencies.

Just my 5 cents.

L.

Hysolid // Mytek Brooklyn // Spectron Musician III // Analysis Audio Omega

RE: Diffusison, posted on October 3, 2016 at 04:31:53

josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010

My original plan was to have the speakers on either side of the fireplace. It actually works out very nicely from a room organization perspective -- as you say, it's a dedicated room so I can do with it what I want but I still have to hang out there and want to do some work there so I can listen to the big speakers so I do want to make it functional.

Unfortunately, when I tried this arrangement with the MMG's it sounded horrible. They just wouldn't image properly with the mantle behind them, no matter what I did. Everything sounded like it was coming from the fireplace. In the end, I figured out that the only thing I could do would be to put bookshelves with doors on either side of the mantle to flush out the wall, and that would mean moving the closet door to the hall -- major demolition in a house with lead paint, of which I've had my fill. Also, as I said, the bass doesn't sound good when the speakers are orientated that way in the room. Very lump in he midbass and no deep bass at all. And it's harder to accommodate the video projector as well.

As you say, I want to aim for an even decay across all frequencies. But I don't yet know what high frequency Rt time I'll have when the furnishings are in place or what I'll aim for so I think I'll wait for the measurements -- my feeling was go for the higher frequency treatment first and then add bass trapping to match. (Bass trapping may also not just be a matter of broadband absorption depending on where the woofers end up living, the right hand woofer develops a one-note midbass boom if it's located in the cavity formed by the mantle and the front wall.)

But right now I'm working on imaging. I'm really very constrained by that! Given the limitations of the room (radiator, mantle, etc.) I don't have much leeway in placement and I can tune EQ, Rt, and diffusion more easily than I can tune the imaging.

RE: Re framing, posted on October 3, 2016 at 09:54:01

Satie
Audiophile

Posts: 5426
Joined: July 6, 2002

There is nearly a foot's worth of MDF you can remove from each speaker by going to a hardwood frame. Also benefit from putting the mid and ribbon closer. Perhaps that is the way to fit the speakers into the room in the equidistant setup. Despite many trials on other setups that is pretty much the go-to for all performance criteria even when the crossover is not quite friendly to it. As Vandersteen and Theil point out there is something fundamentally right about physically time aligned designs that does not quite happen without it.

RE: Re framing, posted on October 3, 2016 at 10:02:43

josh358
Industry Professional

Posts: 12332
Joined: February 9, 2010

The equidistant setup certainly works sonically but it destroys the room, almost bisects it and blocks a window. I'm going to try it further back -- I'd tried it at 3' which as you might expect was terrible (easy to do because that's where the woofers were at the time) but not at 4' or 6', only at 5', and not with diffusion. I'm thinking that 3' or 4' might work with diffusion and that becomes practical.

New wood NT panels would be nice and it would be great to put the mids and tweeters closer together. (BTW, anyone know what the trim strip between the mid and tweeter in the 3.x and 20.x does? Is it there for structural reasons?) However, another big project I don't have time for, busy today installing the fireplace and I haven't even fixed the delam on the woofers.

Whatever I do, it will ultimately be time aligned with the MiniDSP, I don't see any way of getting this room to work without that.

RE: Re framing, posted on October 6, 2016 at 11:26:40
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	Isn't frame width related to front/back cancelation frequency? Too much is never enough

RE: Re framing, posted on October 6, 2016 at 14:26:37
Satie Audiophile Posts: 5426 Joined: July 6, 2002	Yes, but less important when you are using wall loading as Josh is doing as dipole cancellation is restricted on one side. .

RE: Re framing, posted on October 6, 2016 at 15:47:20
pictureguy Audiophile Posts: 22597 Location: SoCal Joined: October 19, 2008	I'm just establishing the principle. And Yes, with the panel using wall loading, that side is pretty much 'out of play'. The reason I ask is that I've seen Panels with 'truncated' frames (Apogee?) which I suspect varies the cancelation frequency. Advantage? Disadvantage? I would design such frames for my 1.6s, if I ever work up the energy to start! Too much is never enough

RE: Re framing, posted on October 6, 2016 at 18:54:53

Satie
Audiophile

Posts: 5426
Joined: July 6, 2002

The trapezoid shaped frame on the Apogee is supposed to spread the baffle loading over a broader range of frequencies rather than have the one freq below which it just falls off.. Other issues are at play but I don't remember what they were. That should complement the room's bass loading and provide a more uniform bass FR - it is sort of a substitute for Magnepan's resonance freq tuning with the buttons. but operates at a different freq range to provide a lower bass emphasis vs more even response on through the midbass on maggies.

I don't expect it would contribute to a maggie reframing project. .

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