[bs0755]

I have been going through the archives, and I have a question regarding absorption/diffusion on the rear wall of my small room (11 1/2' X 13 1/2' X 9').  I currently have a mixture of 4" panels from ATS, and GIK Tri Traps (2 stacked in all of the corners). The recommendation of my speaker builder (Merling TSMs) is to use absorption on the front wall behind the speakers, and at the first two reflection points on the side walls. I was advised to also uses a small amount of absorption on the rear wall directly above my head--since the size/configuration of the room dictates that my couch be against the rear wall. Ideally, with the TSMs, there would be no absorption on the rear wall, so I am wondering if some D1 Diffusors, placed above the absorption panels would be beneficial in taming comb filtering? From what I have been able to ascertain, I would be sitting too close to the wall to benefit from the diffusors, but for the price, I would be willing to give the D1s a try--unless it would be a total waste of money...Thanks in advance for any input!

[John Casler]

I have been going through the archives, and I have a question regarding absorption/diffusion on the rear wall of my small room (11 1/2' X 13 1/2' X 9').  I currently have a mixture of 4" panels from ATS, and GIK Tri Traps (2 stacked in all of the corners). The recommendation of my speaker builder (Merling TSMs) is to use absorption on the front wall behind the speakers, and at the first two reflection points on the side walls. I was advised to also uses a small amount of absorption on the rear wall directly above my head--since the size/configuration of the room dictates that my couch be against the rear wall. Ideally, with the TSMs, there would be no absorption on the rear wall, so I am wondering if some D1 Diffusors, placed above the absorption panels would be beneficial in taming comb filtering? From what I have been able to ascertain, I would be sitting too close to the wall to benefit from the diffusors, but for the price, I would be willing to give the D1s a try--unless it would be a total waste of money...Thanks in advance for any input!

As funny as it may sound, I'd take at least a Queen sized mattress and place it behind the couch in front of the wall.  Cover it with something attractive, and be prepared for a shocking difference (to the better) with your sound. (Make sure it has no plastic cover)

Having the couch against the rear wall is devastating to most systems.  The only way to begin to hear your systems potential is to use a fairly broad band (mattress) absorber.

Having a hard surface reflection so close to the ears (as in right behind them) will alter the sound more than most other problems.

May sound like a funny idea, but will "actually sound" remarkable.  And if you have a spare bedroom you can "steal" the mattress for a few sessions at no cost.

PS; doesn't work with the new Sleep Comfort air mattress systems

[Hipper]

I had a small room set up, 13' x 8' x8' and put the speakers in the corners on the long side with my listening chair (single seat) against the other wall. There was acoustic foam on the wall behind the speakers and my chair was tall enough to prevent rear wall reflections. These reflections may have been unlikely anyway because of the 8' distance between the two walls and the angle of the speakers to the side walls. It was in fact a nearfield set up (there are some pictures of it in my gallery).

I've since moved into a bigger room and initially tried to repeat the set up (which includes a digital equalizer). This involved trying to prevent ceiling and side wall reflections with acoustic foam. However, results have not been as good as I'd hoped. After reading Floyd Toole's book, 'Sound Reproduction', I've been re-thinking my ideas. In particular he suggests that side wall reflections are a good thing so I've removed the ceiling and side wall foam and remeasured with the equalizer, and whilst I'm not there yet I think my brain is now adapting to the new sounds and I'm getting there.

So, my current view, for what it's worth, is absorption behind the speakers and your head (with chair, acoustic foam or mattress!) and carpet (I have sonic insulation under the carpet as I live in a first floor flat [apartment]) but leave the ceilings and side walls alone. I'd recommend an equalizer too (I use a Behringer DEQ2496 - about $300).

[bs0755]

As funny as it may sound, I'd take at least a Queen sized mattress and place it behind the couch in front of the wall.  Cover it with something attractive, and be prepared for a shocking difference (to the better) with your sound. (Make sure it has no plastic cover)

Having the couch against the rear wall is devastating to most systems.  The only way to begin to hear your systems potential is to use a fairly broad band (mattress) absorber.

Having a hard surface reflection so close to the ears (as in right behind them) will alter the sound more than most other problems.

May sound like a funny idea, but will "actually sound" remarkable.  And if you have a spare bedroom you can "steal" the mattress for a few sessions at no cost.

PS; doesn't work with the new Sleep Comfort air mattress systems
 
Thanks!

I do have approximately 2' X 8' of absorption right above my head--I am just wondering how diffusion would work on the rest of the wall...

[InfernoSTi]

I recall reading that diffusion needs space to sound "normal" if that makes since.  So the deeper the diffusion, the farther away you need to be.  I think it was something like a foot for every inch of diffusion depth (4 feet for 4" deep diffusors and 6' for 6" deep diffusors....don't quote me, this is just my fuzzy recollection).  I was looking for a 1" or 2" diffusor and couldn't find one until I came across the RPG BAD panel diffusor.  I haven't ordered one (or two) but that is what I am thinking about getting if I go with a diffusor, particularly behind my listening position in a space less than 6 feet from the rear wall. 

I have no affiliation with RPG, btw, and like you, I have ATS panels and soon GIK Tri Traps (on order  ). To be clear, I don't have these so I'm not vouching for their effectiveness but they do seem well received and have been in the market for years. They come in up to 4" depths, which is what I was considering, but the diffusion is similar for all depths (just the bass absorption changes). 

Here is the link to the RPG BAD panel diffusor white paper so you can start reading about it yourself to see if it seems useful:

Part 1: http://www.rpginc.com/research/6i2.htm
Part 2: http://www.rpginc.com/research/6i3.htm
Part 3: http://www.rpginc.com/research/7i3.htm

I think reading all three parts is useful, as Part 1 covers the basics and Part 3 contains good information on the deeper panels tested in response to user queries.

Good luck with your room!

John

[bpape]

That's correct.  Never worked out the that rule of thumb but it doesn't sound far off.  It's actually related to how low a diffuser will erach and the resulting wavelengths vs the distance from the diffusion to your ears.

Bryan

[youngho]

I recall reading that diffusion needs space to sound "normal" if that makes since.  So the deeper the diffusion, the farther away you need to be.  I think it was something like a foot for every inch of diffusion depth (4 feet for 4" deep diffusors and 6' for 6" deep diffusors....don't quote me, this is just my fuzzy recollection).  I was looking for

I gave my copy of Floyd Toole's book "Sound Reproduction" to a friend, but in it, he quotes Peter D'Antonio and Trevor Cox suggesting that "listeners should be placed as far from scattering surfaces as possible, at least three wavelengths away...in some situations, this distance may have to be compromised." As Toole notes, that's at least 10 ft for a diffuser effective to 300-500 Hz.

[face]

Perfect timing with this topic.  I'm only about 3' from my rear wall and am getting the itch to try something different.  I tried absorption on the rear wall and it made the room sound too dead.  I have one pair of foam diffusors back there now, I was considering picking up another pair but I'm not too fond of the appearance.  How's RPG's pricing?

[richidoo]

Since the BAD panel absorbs below where it stops diffusing it actually works well close behind the head. Even a foot away sounds good. Frequencies too low to diffuse are absorbed, but higher freqs are reflected or diffused. So it stops the echo but it can't be "felt" behind you like pure absorption. The nice thing about it is that it is thin.  But when you want diffusion for diffusion sake like ceiling, sidewalls, etc then a good phase diffusor is more efficient diffusor.

[InfernoSTi]

Well, they aren't cheap!

A quick Google search showed a variety of suppliers and products.  The 4" flat panel is the most appealing to me (about $600 for a pair of 2'x4'x4")

Standard 1"
http://www.fullcompass.com/search.php?txtAll=RPG+Flat&txtBrand=RPG&sortOrder=

Standard 2"
http://www.bhphotovideo.com/c/search?Ntt=RPG+BAD&N=0&InitialSearch=yes

Bass Trap 4"
http://www.acousticfrontiers.com/RPG-BAD-Panel-4-thick-24-x-48.html

Curved Model
http://www.gcaudio.com/cgi-bin/store/showProduct.cgi?id=371

I will reiterate, this is a product I've been looking closely at but have not yet ordered/tried. 

Cheers,
John

EDIT: while I was typing this, Rich posted...nice info, Rich, thank you!

[face]

Thanks for the responses guys.  Fortunately I'd only be interested in the 1-2" models and their prices are just a little above what I expected.  Glad I don't need the 4" models.   

[bs0755]

Thanks for all of the responses so far!

I am still trying to get a grasp on diffusion and comb filtering, so I will try and ask my question a different way:

I understand that my room is not big enough to reap the positve potential of diffusion--However, would diffusors help to negate comb filtering and/or slap echo?

Thanks again!

[bpape]

Up high the diffusion can certainly help mitigate slap echo. 

Bryan