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DIY Binary Amplitude Diffuser anyone?
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jrubbernek
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#1
6th June 2009
Old 6th June 2009
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DIY Binary Amplitude Diffuser anyone?

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...
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6th June 2009
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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!
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8th June 2009
Old 8th June 2009
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Quote:
Originally Posted by jayfrigo View Post
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?
#4
8th June 2009
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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.
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10th June 2009
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Quote:
Originally Posted by jrubbernek View Post
I'd love to figure out how to make these though...any tips?
Cox and D'Antonio's book.
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29th July 2011
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Quote:
Originally Posted by jayfrigo View Post
.........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...

Sequence:

Code:
position:126 ***** 1
position:125 ***** 0
position:124 ***** 0
position:123 ***** 0
position:122 ***** 0
position:121 ***** 0
position:120 ***** 0
position:119 ***** 1
position:118 ***** 0
position:117 ***** 0
position:116 ***** 0
position:115 ***** 0
position:114 ***** 0
position:113 ***** 1
position:112 ***** 1
position:111 ***** 0
position:110 ***** 0
position:109 ***** 0
position:108 ***** 0
position:107 ***** 1
position:106 ***** 0
position:105 ***** 1
position:104 ***** 0
position:103 ***** 0
position:102 ***** 0
position:101 ***** 1
position:100 ***** 1
position:099 ***** 1
position:098 ***** 1
position:097 ***** 0
position:096 ***** 0
position:095 ***** 1
position:094 ***** 0
position:093 ***** 0
position:092 ***** 0
position:091 ***** 1
position:090 ***** 0
position:089 ***** 1
position:088 ***** 1
position:087 ***** 0
position:086 ***** 0
position:085 ***** 1
position:084 ***** 1
position:083 ***** 1
position:082 ***** 0
position:081 ***** 1
position:080 ***** 0
position:079 ***** 1
position:078 ***** 0
position:077 ***** 0
position:076 ***** 1
position:075 ***** 1
position:074 ***** 1
position:073 ***** 1
position:072 ***** 1
position:071 ***** 0
position:070 ***** 1
position:069 ***** 0
position:068 ***** 0
position:067 ***** 0
position:066 ***** 0
position:065 ***** 1
position:064 ***** 1
position:063 ***** 1
position:062 ***** 0
position:061 ***** 0
position:060 ***** 0
position:059 ***** 1
position:058 ***** 0
position:057 ***** 0
position:056 ***** 1
position:055 ***** 0
position:054 ***** 0
position:053 ***** 1
position:052 ***** 1
position:051 ***** 0
position:050 ***** 1
position:049 ***** 1
position:048 ***** 0
position:047 ***** 1
position:046 ***** 0
position:045 ***** 1
position:044 ***** 1
position:043 ***** 0
position:042 ***** 1
position:041 ***** 1
position:040 ***** 1
position:039 ***** 1
position:038 ***** 0
position:037 ***** 1
position:036 ***** 1
position:035 ***** 0
position:034 ***** 0
position:033 ***** 0
position:032 ***** 1
position:031 ***** 1
position:030 ***** 0
position:029 ***** 1
position:028 ***** 0
position:027 ***** 0
position:026 ***** 1
position:025 ***** 0
position:024 ***** 1
position:023 ***** 1
position:022 ***** 1
position:021 ***** 0
position:020 ***** 1
position:019 ***** 1
position:018 ***** 1
position:017 ***** 0
position:016 ***** 0
position:015 ***** 1
position:014 ***** 1
position:013 ***** 0
position:012 ***** 0
position:011 ***** 1
position:010 ***** 0
position:009 ***** 1
position:008 ***** 0
position:007 ***** 1
position:006 ***** 0
position:005 ***** 1
position:004 ***** 1
position:003 ***** 1
position:002 ***** 1
position:001 ***** 1
position:000 ***** 1


here are some examples:









Good luck!

Boggy
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Better control room needs:
-a much smaller desk
-speaker stands
-best possible position for loudspeakers and yourself
-a broader and thicker cloud
-a broader and thicker wall panels
-more super chunks in all corners
-a binary diffuser slats over proposed treatment
-to not expect "sensational" response
-good luck!
#7
30th July 2011
Old 30th July 2011
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Ta

Thanks Boggy.
DD
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30th July 2011
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2nd August 2012
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Quote:
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?
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2nd August 2012
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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.
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31st August 2012
Old 31st August 2012
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Quote:
Originally Posted by boggy View Post
here are some examples:

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?
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31st August 2012
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Quote:
Originally Posted by Syncamorea View Post
Boggy, those are beautiful treatments.
Thank you very much!
Quote:
Originally Posted by Syncamorea View Post
Did you do the design and build of them?
We (MyRoom Acoustics) design them. Local carpenters build them.
Quote:
Originally Posted by Syncamorea View Post
Are you happy with their performance?
My customer is happy with their performance.
Quote:
Originally Posted by Syncamorea View Post
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 View Post
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 View Post
Behind the black fabric - is that just an everyday ordinary broadband absorber?
It depends... In this particular case, yes, it is.

Cheers!

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31st August 2012
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Syncamorea, my reaction about Boggys binary treatment was about the same as yours when I came across it at another forum: Need an opinion on a small live room acoustics plan (3D sketch included)

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?

I posted my result of Boggys series here: My home made diffuser (there is also an excel spread sheet I wrote for quick and easy calculations on dimensions).
#14
2nd September 2012
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Hi Adhoc,

I tried your spreadsheet, but when I enter a number in cell k2, there is something wrong with cell L2. What did I wrong?

Best regards,

Peter
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2nd September 2012
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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 "."
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2nd September 2012
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Thanks, Adhoc. More pieces for the puzzle!
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5th September 2012
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Adhoc,

I found the problem, in L2 stands a "strange" word, which implicates round off.

Best regards,

Peter
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5th September 2012
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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.
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5th September 2012
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Yes! That was the word my Excel didn't know. Thanx for the spreadsheet.
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18th October 2012
Old 18th October 2012
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Quote:
Originally Posted by boggy View Post
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...

Sequence:

Code:
position:126 ***** 1
position:125 ***** 0
position:124 ***** 0
position:123 ***** 0
position:122 ***** 0
position:121 ***** 0
position:120 ***** 0
position:119 ***** 1
position:118 ***** 0
position:117 ***** 0
position:116 ***** 0
position:115 ***** 0
position:114 ***** 0
position:113 ***** 1
position:112 ***** 1
position:111 ***** 0
position:110 ***** 0
position:109 ***** 0
position:108 ***** 0
position:107 ***** 1
position:106 ***** 0
position:105 ***** 1
position:104 ***** 0
position:103 ***** 0
position:102 ***** 0
position:101 ***** 1
position:100 ***** 1
position:099 ***** 1
position:098 ***** 1
position:097 ***** 0
position:096 ***** 0
position:095 ***** 1
position:094 ***** 0
position:093 ***** 0
position:092 ***** 0
position:091 ***** 1
position:090 ***** 0
position:089 ***** 1
position:088 ***** 1
position:087 ***** 0
position:086 ***** 0
position:085 ***** 1
position:084 ***** 1
position:083 ***** 1
position:082 ***** 0
position:081 ***** 1
position:080 ***** 0
position:079 ***** 1
position:078 ***** 0
position:077 ***** 0
position:076 ***** 1
position:075 ***** 1
position:074 ***** 1
position:073 ***** 1
position:072 ***** 1
position:071 ***** 0
position:070 ***** 1
position:069 ***** 0
position:068 ***** 0
position:067 ***** 0
position:066 ***** 0
position:065 ***** 1
position:064 ***** 1
position:063 ***** 1
position:062 ***** 0
position:061 ***** 0
position:060 ***** 0
position:059 ***** 1
position:058 ***** 0
position:057 ***** 0
position:056 ***** 1
position:055 ***** 0
position:054 ***** 0
position:053 ***** 1
position:052 ***** 1
position:051 ***** 0
position:050 ***** 1
position:049 ***** 1
position:048 ***** 0
position:047 ***** 1
position:046 ***** 0
position:045 ***** 1
position:044 ***** 1
position:043 ***** 0
position:042 ***** 1
position:041 ***** 1
position:040 ***** 1
position:039 ***** 1
position:038 ***** 0
position:037 ***** 1
position:036 ***** 1
position:035 ***** 0
position:034 ***** 0
position:033 ***** 0
position:032 ***** 1
position:031 ***** 1
position:030 ***** 0
position:029 ***** 1
position:028 ***** 0
position:027 ***** 0
position:026 ***** 1
position:025 ***** 0
position:024 ***** 1
position:023 ***** 1
position:022 ***** 1
position:021 ***** 0
position:020 ***** 1
position:019 ***** 1
position:018 ***** 1
position:017 ***** 0
position:016 ***** 0
position:015 ***** 1
position:014 ***** 1
position:013 ***** 0
position:012 ***** 0
position:011 ***** 1
position:010 ***** 0
position:009 ***** 1
position:008 ***** 0
position:007 ***** 1
position:006 ***** 0
position:005 ***** 1
position:004 ***** 1
position:003 ***** 1
position:002 ***** 1
position:001 ***** 1
position:000 ***** 1



Good luck!

Boggy
Hi,

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...
#21
18th October 2012
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Quote:
Originally Posted by bebbo View Post
Hi,

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.


Sent from my ST18i
#22
18th October 2012
Old 18th October 2012
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Quote:
Originally Posted by boggy View Post
Yes, of course. Sequence is much longer, actually.


Sent from my ST18i
Thanks!
#23
8th January 2013
Old 8th January 2013
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Quote:
Originally Posted by boggy View Post
Yes, of course. Sequence is much longer, actually.


Sent from my ST18i
On your pics you have 2 different thickness strips of wood in the different rooms. What determines the choice, how much of the highs you want to keep?
#24
8th January 2013
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Quote:
Originally Posted by GreenNeedle View Post
On your pics you have 2 different thickness strips of wood in the different rooms. What determines the choice, how much of the highs you want to keep?
It is usually availability of wooden strips... 1-3cm is a common thickness I use.
#25
12th January 2013
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Thank you.
#26
11th October 2013
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Quote:
Originally Posted by boggy View Post
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?
#27
12th October 2013
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Quote:
Originally Posted by chasethompsonaud View Post
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 View Post
......... 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 View Post
(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....




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16th October 2013
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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 View Post
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...

Sequence:

Code:
position:126 ***** 1
position:125 ***** 0
position:124 ***** 0
position:123 ***** 0
position:122 ***** 0
position:121 ***** 0
position:120 ***** 0
position:119 ***** 1
position:118 ***** 0
position:117 ***** 0
position:116 ***** 0
position:115 ***** 0
position:114 ***** 0
position:113 ***** 1
position:112 ***** 1
position:111 ***** 0
position:110 ***** 0
position:109 ***** 0
position:108 ***** 0
position:107 ***** 1
position:106 ***** 0
position:105 ***** 1
position:104 ***** 0
position:103 ***** 0
position:102 ***** 0
position:101 ***** 1
position:100 ***** 1
position:099 ***** 1
position:098 ***** 1
position:097 ***** 0
position:096 ***** 0
position:095 ***** 1
position:094 ***** 0
position:093 ***** 0
position:092 ***** 0
position:091 ***** 1
position:090 ***** 0
position:089 ***** 1
position:088 ***** 1
position:087 ***** 0
position:086 ***** 0
position:085 ***** 1
position:084 ***** 1
position:083 ***** 1
position:082 ***** 0
position:081 ***** 1
position:080 ***** 0
position:079 ***** 1
position:078 ***** 0
position:077 ***** 0
position:076 ***** 1
position:075 ***** 1
position:074 ***** 1
position:073 ***** 1
position:072 ***** 1
position:071 ***** 0
position:070 ***** 1
position:069 ***** 0
position:068 ***** 0
position:067 ***** 0
position:066 ***** 0
position:065 ***** 1
position:064 ***** 1
position:063 ***** 1
position:062 ***** 0
position:061 ***** 0
position:060 ***** 0
position:059 ***** 1
position:058 ***** 0
position:057 ***** 0
position:056 ***** 1
position:055 ***** 0
position:054 ***** 0
position:053 ***** 1
position:052 ***** 1
position:051 ***** 0
position:050 ***** 1
position:049 ***** 1
position:048 ***** 0
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Attached Files
File Type: zip MLS.zip (1.1 KB, 61 views)
#29
17th October 2013
Old 17th October 2013
  #29
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Quote:
Originally Posted by robertopisa View Post
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
Thanks!


#30
6th March 2014
Old 6th March 2014
  #30
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Vertical or horizontal slats on the front wall?

Hello Boggy,

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 04:53 PM.. Reason: Added reference
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