for home made diffuser....

[vegafreak]

Will styrofoam or cardboard egg cartons work better. Anyone know?

[Yonce N Mild]

I think the egg cartons would do better at creating a fire hazard although the Styrofoam will probably give off more noxious gasses so I guess it is a wash.
You have homework to do. Start here: http://www.ethanwiner.com/acoustics.html

[Massive Master]

Neither are diffusive - Both are hazardous.

Egg cartons and Styrofoam only really work in the movies...

[Ethan Winer]

Originally Posted by vegafreak

Will styrofoam or cardboard egg cartons work better. Anyone know?

All About Diffusion

--Ethan

[vegafreak]

Originally Posted by Ethan Winer

All About Diffusion

--Ethan

Thanks Ethan, great article. I really appreciate the work that you do! I'm thinking with my tiny control room I won't need any diffusion at all.

[bkkornaker]

try a foam mattress pad.

they make those eggcrate foam mattress pads, looks identical to expensive diffusers.....

much cheaper, although im sure the material is not the same....

but close...

http://www.nextag.com/egg-crate-foam...ad/search-html

[NL5]

Originally Posted by bkkornaker

try a foam mattress pad.

they make those eggcrate foam mattress pads, looks identical to expensive diffusers.....

much cheaper, although im sure the material is not the same....

but close...

http://www.nextag.com/egg-crate-foam...ad/search-html

Bad, bad, bad idea.......

[bkkornaker]

Originally Posted by NL5

Bad, bad, bad idea.......

really? why?

the lock out studio (for jamm rooms) i go to in Burbank, CA has them hung on the interior walls. i asked the guy what is was (cause it looked like eggcrate foam mattress pads)....

and sure enough.....he confessed it was.

cheap bastard.....

[Dogbreath]

Different material, I'm thinkin.

I think all it really does is knock off some highs.

If you've got a small control room......bass traps.
Diffusion may not be needed. And if it is, I'm thinkin not much.

Trap the corners mang....your mixes will come together much easier.

all in my humble opinion, of course.

[Chili]

Originally Posted by bkkornaker

really? why?

the lock out studio (for jamm rooms) i go to in Burbank, CA has them hung on the interior walls. i asked the guy what is was (cause it looked like eggcrate foam mattress pads)....

and sure enough.....he confessed it was.

cheap bastard.....

That kind of foam doesn't have the density to attenuate sound. Maybe only high freq stuff, but anything lower will go right through it.

If I recall my old physics, the actual mechanism that attenuates sound is when the energy passes from one medium to another. A little bit will be absorbed, a little bit reflected, and a lot converted to heat as it moves the medium. The greater the difference in densities of the mediums, the greater the attenuation. The more mediums the sound has to pass through the greater the attentuation.

The acoustic foam is closed cell, the material is more dense and there is many more air pockets than that mattress foam. Foam is basically made up of plastic with lots of air pockets. Sound traverses through both... plastic - air- plastic - air - plastic, etc. So when sound energy passes through, more energy is dissipated because it takes more energy to move the material (converting to heat) and it occurs many more times as it passes through the air pockets.

I'm guessing that rigid fiberglass boards work well because the fibers are so closely woven together that air movement is restricted, plus they are so thick there are a lot of medium interfaces that the sound passes through. Fiber-air-fiber-air-fiber-air, etc.

Hmmm, not so easy to explain in a post.

[NL5]

Originally Posted by bkkornaker

dumb bastard.....

Ask him if it meets fire code. Then watch him start to shit himself. It'll be great.

Go check out Ethan's site. There is some great info there.

[SouthSIDE Glen]

Originally Posted by Chili

If I recall my old physics, the actual mechanism that attenuates sound is when the energy passes from one medium to another. A little bit will be absorbed, a little bit reflected, and a lot converted to heat as it moves the medium. The greater the difference in densities of the mediums, the greater the attenuation. The more mediums the sound has to pass through the greater the attentuation.

You remember the physics fairly well, but if my memory serves half as well, you are kinda throwing two parts absorption and one part diffusion into one pot there.

Now, the name of this thread deals with diffusion. Whether this is because vegafreak actually means diffusion or whether he's actually looking for absorption, I don't know. But strictly speaking, diffusion does not require any absorption (though there usually is at least some, whether incidental or intentional). The main purpose for diffusion panels is to break up directional reflections - i.e. to diffuse the sound in the room rather than reflecting it like laser beams in a mirror. (Also, by definition, this is intended only for those higher frequencies prone to such direct reflection issues.)

This is why diffusion panels tend to come in a few popular designs. One is a randomly irregular surface, not the pyramids of absorber panels which are designed to trap sound, but rather something like a chessboard with each square sticking out a different distance. The ireregular surface means the sound hits each block at a slightly different angle, and therefore reflects back at a slightly different angle than it's neighbor. This diffuses the sound in the room. These can be easily made by buying yourself a 2x2, cutting it into many irregular lengths from 1" to a few inches and then gluing them together in a checkerboard pattern with some carpenter's glue.

Another is a simple convex curved surface bowed in towards the room. Sound hitting each point on the curve will be reflected at a slightly different angle. Also fairly easily made by buying a 2'x4' sheet of hardwood (not plywood), steam/soaking it until it's pliable and bending it into a curve around a shaped 2x4 cut into the desired a curve shape. Clamp into place and let dry.

Note the the wood ones will be almost pure diffusers, not a lot of absorption going on. If you want some absorption as well, they can be made of more porous and energy absorbing material. But absorption is not always a wonderful idea. We have all talked about the curses of an overly-dead room. If you want to keep some liveliness without the problems of slapback, comb filtering and other first-reflection problems, a pure diffuser is just the ticket.

G.

[NL5]

Originally Posted by SouthSIDE Glen

These can be easily made by buying yourself a 2x2, cutting it into many irregular lengths from 1" to a few inches and then gluing them together in a checkerboard pattern with some carpenter's glue.

Not to poo poo on a pretty good post, but I was under the impression that it was WAY more complex than that. I thought there was some kinda crazy algorithm that determined the length of each block. Or am I mis-remembering?

[Chili]

Originally Posted by SouthSIDE Glen

You remember the physics fairly well, but if my memory serves half as well, you are kinda throwing two parts absorption and one part diffusion into one pot there.

G.

Thanks G. Nah, I wasn't referring to diffusion at all. I know it's totally different from absorption. I was replying to bkkornaker's post about the mattress foam and why it's not a good candidate from sound absorption. Then I just threw out useless information on why some stuff works and others don't. Essentially, hijacking the thread.

Cheers,

[Dogbreath]

No Hijacking.

I'll report you to a mod.

[SouthSIDE Glen]

Originally Posted by NL5

Not to poo poo on a pretty good post, but I was under the impression that it was WAY more complex than that. I thought there was some kinda crazy algorithm that determined the length of each block. Or am I mis-remembering?

Good point. I'm sure that there's math to ensure a high degree of randomness; i.e. that if you have a block of length x and a block of length y, you don't want to have them spread z inches apart because they will just wind up reflecting back at the same angle, and stuff like that. Also the size of the squares themselves may play a part in bandwidh limiting the effectiveness of the diffusion, I would guess. I'm sure such math could be found on the Internet.

Personally, I find that a bookshelf or bookcase tends to do the job fairly well too .

Originally Posted by Chili

Thanks G. Nah, I wasn't referring to diffusion at all. I know it's totally different from absorption. I was replying to bkkornaker's post about the mattress foam and why it's not a good candidate from sound absorption. Then I just threw out useless information on why some stuff works and others don't. Essentially, hijacking the thread.

My fault for not reading the whole tread from the beginning, Chili. Sorry 'bout that. Not that I was criticizing to begin with or anything, I didn't mean to single you out.



G.

[Chili]

Originally Posted by Dogbreath

No Hijacking.

I'll report you to a mod.

And you know what's funny is I don't get notifications for reported threads. MSHilarious got them for one day. So, go ahead, report me. But, really, we told France and hopefully they'll get it fixed soon.

Originally Posted by SouthSIDE Glen

I didn't mean to single you out.



G.

I know....

Originally Posted by NL5

Not to poo poo on a pretty good post, but I was under the impression that it was WAY more complex than that. I thought there was some kinda crazy algorithm that determined the length of each block. Or am I mis-remembering?

Yeah, i remember seeing a matrix posted somewhere, but I couldn't find it. You're right, it's not random.

Bringing this back to the original post (so I'm not hijacking anymore), I don't think the OP needs diffusion. Based on his other threads, he's got a small room and according to Ethan, absorption is the best method tuning the room. Do I have that right?

Cheers,

[SouthSIDE Glen]

Originally Posted by Chili

Bringing this back to the original post (so I'm not hijacking anymore), I don't think the OP needs diffusion. Based on his other threads, he's got a small room and according to Ethan, absorption is the best method tuning the room. Do I have that right?

I think the short answer is, "It depends...."

Absorption in terms of bass trapping, sure. And if a room winds up being extremely bright like a walk-in plate chamber, then sure some percentage of HF absorption/deadening will probably help. But one usually doesn't want overly dead rooms, either. I've never seen or heard of an engineer or acoustic designer actually advocating working within an anechoic chamber for anything but laboratory testing. IMHO, the goal is to eliminate *problems* (such as bass modality, comb filtering, standing waves and such) without creating such an artificial-sounding space as to sound unnatural to the ears. Some degree of ambiance is desirable. Hence the difference between using absorption and diffusion in certain situations.

G.

[bkkornaker]

Title= "for home made diffuser...."

so what are we talking about here? diffusion? or absorption?

and what the heck is the difference (if any)?

[SouthSIDE Glen]

Originally Posted by bkkornaker

Title= "for home made diffuser...."

so what are we talking about here? diffusion? or absorption?

and what the heck is the difference (if any)?

Go back and re-read the last few posts, it's all pretty much spelled out. But in short, absorption stops sound from reflecting by absorbing it's energy, diffusion doesn't stop reflection but it diffuses the reflected energy in many different directions, rendering it fairly harmless without absolutely getting rid of it. Absorption deadens sound, diffusion de-focuses it.

G.

[SouthSIDE Glen]

Originally Posted by NL5

Not to poo poo on a pretty good post, but I was under the impression that it was WAY more complex than that. I thought there was some kinda crazy algorithm that determined the length of each block. Or am I mis-remembering?

I got very little sleep last night, and it's all your fault, NL5 . I decided to do some research and reading up on skyline diffuser panel design.Here's what I get out of it thus far:

Yeah, many companies have filed patents on fancy prime number-based algorithms for determining block size. Mostly these algorithms are used as pseudo random number generators to help ensure a fairly natural randomness in block size and to help ensure uniqueness in block size.

While this is very nice, it's not absolutely necessary to achieve serviceable diffusion. It's kind of a measure of smoothness of the diffusion. For the best in smooth diffusion, you can spend $150 for a 2x2 panel of stiff foam that follows a patented randomness design. For effective enough diffusion that may not have the absolute ultimate in smoothness, but for most applications will be effective enough to effectively reduce or eliminate the actual first reflection and comb filtering problems that such diffusers are meant to address, you can build your own without having to use a fancy patented algorithm.

This board, besides depriving me of sleep, is constantly giving me ideas for projects to work on. It seems to be that writing a little program/applet that generated a quite effective cutting plan for building a simple random skyline diffuser panel without violating anybody's patents should be pretty easy to develop. I'll add that to my to do list and hopefully get to it someday...

G.

[Sonixx]

for a small room and specifically with similar dimensions or dimensions that are divisible by a common divisor, the Bottom is very problematic and depending on locations, you can have a lot or very little bottom reinforcement. i.e. you can't trust what you're hearing. the room just does not want to support the longer wave length frequencies evenly. modes are not sufficiently close and in enough quantity.

overall, you need a combination of Bass treatment, Absorption and Diffusion. The Bottom will be the biggest challenge.

back to diffusion, I have built Quadratic Residue Diffusers. below is a small one. the depth determines the bottom frequency diffused.

you really can't expect to get much from just putting up irregularly shaped patterns on the wall.



Here's some larger QRD in action next to 4" deep absorbers.

[SouthSIDE Glen]

OK, here's a specific plan for making a skyline diffuser using nine standard (American) 2'x2s and a piece of plywood using the same "primitive root" algorithm used by the Big Boys.

The effective low frequency handled by such diffusers is determined by well depth (block height). The effective high frequency is determined by well/block width.

Since the effective actual width of each side of a 2x2 in the States is 1.5", this makes the effective upper frequency diffused by such block sizes to be about 4.5kHz. Not too bad. This wont diffuse sibilance, but it covers most of the harsh upper mids below 5kHz.

For the low frequency, you can adjust the lengths of the blocks - the longer they are overall, the lower the lowest diffused frequency. The following numbers cover all the way down to 500Hz. Most of what lies below that should be trapped instead of diffused anyway.

To make a diffusion panel about 19.5" x 18" (roughly) that covers this low of a frequency will require a total of just over 87 feet of 2x2, or nine 8ft lengths. Here's how to cut those 2x2s into the size chunks you need for the diffuser. The first number is the length of the chunk in centimeters, the second number is the number of chunks of that length you'll need:

0 cm: 2
1 cm: 4
2 cm: 5
3 cm: 5
4 cm: 4
5 cm: 5
6 cm: 4
7 cm: 5
8 cm: 5
9 cm: 4
10 cm: 5
11 cm: 4
12 cm: 5
13 cm: 5
14 cm: 4
15 cm: 5
16 cm: 4
17 cm: 5
18 cm: 5
19 cm: 4
20 cm: 5
21 cm: 4
22 cm: 5
23 cm: 5
24 cm: 4
25 cm: 5
26 cm: 5
27 cm: 4
28 cm: 5
29 cm: 4
30 cm: 5
31 cm: 5
32 cm: 4
33 cm: 5
34 cm: 2

Note that there are a couple of wells of 0 centimeters. Unless you want to leave unsightly holes in your skyline where the 0 cm wells go, you can mount all these blocks on a backing piece of plywood or hardwood sheet.

Finally, we need to know the randomized order in which these blocks are mounted together into the final checkerboard. Here's the pattern determined by the prime root algorithm (each number representing the length in centimeters of each block):

1 33 15 16 8 17 13 5 15 30 5 7 5
24 5 28 8 11 7 19 32 23 7 12 26 3
14 17 27 2 5 21 2 25 24 12 34 28 28
4 2 18 33 8 25 4 9 24 19 25 32 3
13 18 12 20 31 4 23 21 9 16 28 20 23
14 31 24 26 31 18 20 11 1 13 12 6 34
33 1 19 18 26 17 21 30 19 4 29 27 29
10 29 7 26 23 27 15 2 11 27 22 8 31
20 17 7 33 29 13 32 9 10 22 0 6 6
30 32 17 1 26 9 30 25 10 15 10 2 31
21 16 22 14 3 30 12 13 25 18 6 14 11
20 3 10 8 3 16 15 23 33 22 22 28 0

If you want to play with the numbers some more, you can find an online calculator here.

G.

[Ethan Winer]

Originally Posted by NL5

I thought there was some kinda crazy algorithm that determined the length of each block.

Not crazy at all, and definitely not random. Download the Acoustic Calculator here:

Acoustic Calculator

Much more about diffusion here:

All About Diffusion

--Ethan

[SouthSIDE Glen]

Originally Posted by Ethan Winer

Not crazy at all, and definitely not random.

Well, certainly pseudo-random (pure randmoness cannot be synthesized). There's importance to the limiting numbers, they are not just random, but the whole point as to the distribution of the numbers in a skyline diffuser is to provide (close enough to) random distribution of the well depths and angles of incidence.

G.