Hi gearslutz, I was browsing around and I stumbled upon a picture of a Binary Amplitude diffuser, does anyone know how to make these, what are the calcutions? it might be a solution for my small drum room. thanks. Your help will be highly appreciated...

These work on amplitude rather than phase (amplitude gratings rather than phase gratings), and scatter above 1 kHz. They are advantageous for some applications because of their limited depth.

They are absorptive below 1 kHz, and based on the depth of absorption behind the grating panel (usually 1-4") they can absorb some bass as well while minimizing absorption above 1 kHz. Size of holes (usually 1/2" or 5/8") affects higher frequency attenuation. These surfaces can also be curved in various ways for some applications.

The idea is to use a binary sequence for the holes that tries to keep the number of ones and zeros even which helps more uniform distribution of the diffuse reflected sound. Hole spacing was originally inspired by Angus' work on MLS (Maximum Length Sequences). Optical sequences usually result in too few 1s in long seuences, and some calculations are likely to result in too many 1s. Generating a familiy of sequences and looking for optimized strings with even numbers of 1s and 0s is necessary.

Some trial and error will be required. Cox/D'antonio suggest that computer searches are a manageable way to do this for sequences up to 20, but finding every possible combination for sequences above 20 becomes unwieldy. For a sequence with 24 1s and 24 0s (N=48), there are 10^13 combinations to search! Wrapping a 1D sequence into a 2D array requires Chinese remainder theorem.

Curved hybrid surfaces, and variations in absorption, including Helmholtz properties and possible hole spacing variations, such as reducing open hole area to increase bass absorption, are the next things to investigate when designing binary amplitude diffusion panels. These things are complicated, time-consuming to design, and it's probably better for sanity's sake to simply buy them from RPG!

These work on amplitude rather than phase (amplitude gratings rather than phase gratings), and scatter above 1 kHz. They are advantageous for some applications because of their limited depth.

They are absorptive below 1 kHz, and based on the depth of absorption behind the grating panel (usually 1-4") they can absorb some bass as well while minimizing absorption above 1 kHz. Size of holes (usually 1/2" or 5/8") affects higher frequency attenuation. These surfaces can also be curved in various ways for some applications.

The idea is to use a binary sequence for the holes that tries to keep the number of ones and zeros even which helps more uniform distribution of the diffuse reflected sound. Hole spacing was originally inspired by Angus' work on MLS (Maximum Length Sequences). Optical sequences usually result in too few 1s in long seuences, and some calculations are likely to result in too many 1s. Generating a familiy of sequences and looking for optimized strings with even numbers of 1s and 0s is necessary.

Some trial and error will be required. Cox/D'antonio suggest that computer searches are a manageable way to do this for sequences up to 20, but finding every possible combination for sequences above 20 becomes unwieldy. For a sequence with 24 1s and 24 0s (N=48), there are 10^13 combinations to search! Wrapping a 1D sequence into a 2D array requires Chinese remainder theorem.

Curved hybrid surfaces, and variations in absorption, including Helmholtz properties and possible hole spacing variations, such as reducing open hole area to increase bass absorption, are the next things to investigate when designing binary amplitude diffusion panels. These things are complicated, time-consuming to design, and it's probably better for sanity's sake to simply buy them from RPG!

Yikes, so for a rooky like me then I should stay away from these diffusers and just stick with RPGs or QRDs?

I'd love to figure out how to make these though...any tips?

The build is fairly straightforward, if tedious making all the holes just right. It's the design that's a pain, laying out the amplitude grating. It may be easier to just copy the sequence of an existing one, but it will be hard to find actual plans online I think. I remember one person trying to do a DIY one, but I'm not sure how he arrived at his sequence. You'd have to double check it to make sure it's not just some random spacing or a poor attempt at a copy, or it won't be very effective.

.........I remember one person trying to do a DIY one, but I'm not sure how he arrived at his sequence.........

DanDan ask me to post binary sequence on Gearslutz forum in thread REW Analysis, then, instead of starting a new thread, I'll use this old one that has a nice explanation of binary diffusers functioning (thanks to jayfrigo ), for posting a part of MLS pseudorandom sequence.

Here are a first 127 members of pseudorandom sequence (MLS) that may be used for building binary diffusers. I hope that this is enough for most applications. If someone need more, please ask, and we will generate more...

Optical sequences usually result in too few 1s in long seuences, and some calculations are likely to result in too many 1s. Generating a familiy of sequences and looking for optimized strings with even numbers of 1s and 0s is necessary.

Some trial and error will be required. Cox/D'antonio suggest that computer searches are a manageable way to do this for sequences up to 20, but finding every possible combination for sequences above 20 becomes unwieldy. For a sequence with 24 1s and 24 0s (N=48), there are 10^13 combinations to search!

Sorry to resurrect an old thread, but surely the most efficient means of generating sequences would be to start off with an even number of 1's and 0's (eg 12 of each) and randomise their position in the sequence rather than attempting to find a contiguous length of evenly distributed 1's and 0's from a random sequence?

The important part is "spectrally flat" (silly word). Although the layout could probably be optimized to take early reflections into account, which would be an intensive experience in mathematics.

Boggy, those are beautiful treatments. Did you do the design and build of them? Are you happy with their performance? My interest is peaked by the fact that those rooms are smallish and I'm trying to understand more about options for diffusion in small rooms. What can you tell me about the construction of those features? Behind the black fabric - is that just an everyday ordinary broadband absorber?

My interest is peaked by the fact that those rooms are smallish and I'm trying to understand more about options for diffusion in small rooms.

Binary type amplitude grating is always ok for small rooms. For QRD or PRD diffusers you need to take care about minimum working frequency (and to adjust it to minimum distance from diffuser)... and they works even better in small rooms...

Quote:

Originally Posted by Syncamorea

What can you tell me about the construction of those features?

Behind wooden strips, you can have simple porous broadband absorber

Quote:

Originally Posted by Syncamorea

Behind the black fabric - is that just an everyday ordinary broadband absorber?

It depends... In this particular case, yes, it is.

It is very simple to DIY and requires very little of tools and carpentry skills. Calculations "by hand" for symmetry can be a bit boring though. –The lumber yard often has a limited number of standard dimensions and one of these you want to fit onto you wall area. => Does any fit, which one, how large a width between 2 or more consecutive slats along the whole series, where on the wall area should the binary MLS sequence begin and end etc?

When you enter a value in cell K2 that value is in mm, which in turn will be recalculated to inches in cell L2. => So if you enter 25 mm by pressing the "black little triangle" in column J (which corresponds to cell K2) you will in cell L2 get the value 0,984 inches. If you enter the value 25,4 mm by writing it into cell K2 you should get the value 1,000" in cell L2. ( If this does not happen, you have probably by mistake erased one or several formulas / calculations. As I wrote under "Use of the spread sheet": Do only enter values in the yellow fields).

Note: For decimals the spread sheet use "," and not "."

Correct, I forgot to mention that. The strange word "MAVRUNDA" (if that is your strange word) = "Swedish excel-language", followed by ;1/64 in the formula, which means round off the calculated value to 1/64 of an inch and then the answer is written out with 3 decimals. -Looks tidier I think, with 3 decimals written out all the time, instead of decimals varying between 0 to 9.

DanDan ask me to post binary sequence on Gearslutz forum in thread REW Analysis, then, instead of starting a new thread, I'll use this old one that has a nice explanation of binary diffusers functioning (thanks to jayfrigo ), for posting a part of MLS pseudorandom sequence.

Here are a first 127 members of pseudorandom sequence (MLS) that may be used for building binary diffusers. I hope that this is enough for most applications. If someone need more, please ask, and we will generate more...

I need a sequence to place diffusion on some porous absorbers, I do not have the space to use the whole sequence, can I take any part of it? for example if I need 30 numbers I just take from 50 to 80...

I need a sequence to place diffusion on some porous absorbers, I do not have the space to use the whole sequence, can I take any part of it? for example if I need 30 numbers I just take from 50 to 80...

Yes, of course. Sequence is much longer, actually.

It is usually availability of wooden strips... 1-3cm is a common thickness I use.

do you know if the thickness of the slats or the space between them affects the diffusion properties at all? if so, do you know how it will affect the diffusion? Is this type of diffusion effective on smaller panels? (eg. if I'm not covering the entire wall from floor to ceiling, but using 2'x4' panels instead) or is it only really effective when applied to an entire wall?

do you know if the thickness of the slats or the space between them affects the diffusion properties at all?

Thickness is one way to have a fairly stiff slat. (EDIT: Theoretically, amplitude grating diffuser will work even with thin slats)
Space between them? Space is regular "zero" in binary sequence, so, yes, it affects diffusion...

Quote:

Originally Posted by chasethompsonaud

......... Is this type of diffusion effective on smaller panels?

I doubt that, phase grating diffusers in smaller panels, performs better

Quote:

Originally Posted by chasethompsonaud

(eg. if I'm not covering the entire wall from floor to ceiling, but using 2'x4' panels instead) or is it only really effective when applied to an entire wall?

I never accept this type of (couple of smaller panels) approach because it is fully ineffective for the SBIR or non resonant interferences, which degrade frequency response at listening place. So, binary diffusers is useful for me to bring back reflections to the listener after I install low frequency trapping over all walls and ceiling, and this is a reason why I treat whole wall (smaller surface is not enough, because room is too dead after only LF treatment)... and this way they are effective and I can share my experience about that. Smaller panels influence can be audible, but this is not the whole goal. First goal is to solve dips in frequency response (non resonant interferences below 200Hz), together with room resonances (resonant interferences below 200Hz), as best as possible... after that... it's about personal preferences....

Thanks Boggy, this is a great sequence. I am attaching a ZIP file with the Python code to generate these M-sequences for any length 2^n - 1. It is a source code found on the net that I modified so as to produce the same format as yours.

-R

Quote:

Originally Posted by boggy

DanDan ask me to post binary sequence on Gearslutz forum in thread REW Analysis, then, instead of starting a new thread, I'll use this old one that has a nice explanation of binary diffusers functioning (thanks to jayfrigo ), for posting a part of MLS pseudorandom sequence.

Here are a first 127 members of pseudorandom sequence (MLS) that may be used for building binary diffusers. I hope that this is enough for most applications. If someone need more, please ask, and we will generate more...

Thanks Boggy, this is a great sequence. I am attaching a ZIP file with the Python code to generate these M-sequences for any length 2^n - 1. It is a source code found on the net that I modified so as to produce the same format as yours.

I have a large 150x200x30 porous absorber (Caruso IsoBond with an internal metal plate resonator) on the front wall between the two speakers.

The sound is a bit dead, but I read here on GS that your binary MLS pattern, which I like, works better when the entire front wall is covered with porous absorber, which is not my case.

I thus decided to use slats with the 534 sequence pattern. My question: between the speakers is it better to have vertical or horizontal slats on the front wall?

I saw pictures for both choices, and I know how their 1D diffusion operates but it is unclear to me which are the advantages of each choice.

Thanks
-Roberto

Edit: The topic of vertical vs horizontal slats is addressed here but mainly for side walls Horizontal versus vertical slats. While most agree that vertical slats are better for side walls, there is no explicit agreement for the front walls. I would opt for horizontal ones but I have no clear argument for that.

Last edited by robertopisa; 6th March 2014 at 05:53 PM..
Reason: Added reference