[JCD]

I was at the library yesterday and saw an article on some DIY projects for both absorption and diffusing. The basis of the article was some work by Dr Floyd Toole. Some of my takeaways were:

1. His absorption panel used regular insulation in a 4 inch deep cabinet. I always thought that stuff wasn't that good for acoustics.
2. His diffuser surprised me even more -- a 4ft tall triangle that was at least 1ft deep (apex to wall) made of thin (?) plywood. I didn't think you could get this basic with a diffuser.
3. Another interesting thing -- he suggests using diffusers at the first reflection points rather than absorption.
4. Absorption was best for behind the speakers.

So items 1-3 were all counter to what I expected.

Anyone have any comments?

 

[Lucky7!]

1: Not having the article in front of me, I don't know what you mean by "regular insulation" except some form of fibreglass batts. Here, you'll find a great link with the measured results of a lot of insulation products with many fairly common products doing well in modest thicknesses down to 125Hz or so.

2: re: the pyramid diffuser, I have less confidence in that based up the type of diffusion used in control rooms and other thoroughly designed and measure environments. Strikes me as sort of a symmetrical (horizontal and vertical) cylindrical diffuser which looks easy to better with a PRD/QRD. Not hard to make either and Collo has some superb design software on his site.

3: Sounds like what his research has shown him and repeated in his book and on Dr Olive's blog.

4: I've long felt this to be the case especially with wide dispersion speakers. You want to get the first reflections far enough away from the original sound that they're not heard as one (Haas window) which either means speakers well into the room, soffit mounted or the wall deadened.

 

[bpape]

1. As thickness increases, the need for density decreases provided the material has good gas flow numbers.

2. This is not diffusion, it's minimal scattering (not even and not dealing with the time domain).

3. Diffusion can work provided the speakers have controlled directivity and have excellent off axis response. Most speakers do not qualify in these areas. Many people want to quote this research without also quoting the caveats. This causes a lot of confusion.

4. Depends on the situation and the type of speaker. If speakers are within 3-4' of a wall behind or beside, you will have SBIR issues which can be addressed with absorption. Dipole/bipolar speakers will have that along with higher frequency comb filtering which can be addressed with either diffusion or absorption depending on preference and situation.

Bryan

 

[MatrixDweller]

A problem with diffusion at the first reflection point is that it's not going to tackle mid/high bass and a QRD or Skyline will be about a foot in depth/height to address 500Hz+ frequencies. Simple diffusion (like a barrel or pyramid diffuser) is not going cut it either unless you're sitting in a small sweet spot. Perfect diffusion, or near perfect, might in theory work better than absorbtion, but to get that type of diffusion they'd need to be 7 feet deep. Not practical in a home theater unless you've got big bucks.

I've found some references to articles that Dr. Floyde Toole has written:

http://www.multimediamanufacturer.com/articles/weinberg-conventioneering.pdf
http://forums.klipsch.com/forums/storage/3/968749/LoudspeakersandRoomsPt1.pdf
http://forums.klipsch.com/forums/storage/3/968751/LoudspeakersandRoomsPt2.pdf
http://forums.klipsch.com/forums/storage/3/968753/LoudspeakersandRoomsPt3.pdf