Small program for QRD diffusers (1D & 2D)

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Re: Small program for QRD diffusers (1D & 2D)

Postby tonio » Sat May 22, 2010 4:33 am

Nice AVI's Bob !! :mrgreen:



Bob wrote:
Eric.Desart wrote:That I don't mount them directly to a backing boundary has a reason.
I've seen you do that, and it never occured to me.


I'm lost here.....
Once you get a difference in impedance, things will happen. Also the edges of reflective polys will scatter (which I count on), which makes them advantageous that you hang them free in space with an irregular pattern versus reflective boundaries. That I don't mount them directly to a backing boundary has a reason.

2nd one is on boundary..
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Going by the animations, use of poly (or diffusers in general ) on a boundary is not preffered? Why do so many studios have QRD's on the rear wall?

T
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Re: Small program for QRD diffusers (1D & 2D)

Postby homestudiobldr » Sat May 22, 2010 5:51 am

With all due respect.....






quote]when I write: " Yes, you like special looking and complicated sounding things." that's because I mean that. You are not triggered here by any experience you have with this kind of devices, but this "Chinese remainder theorem" triggers you. For what?[/quote]

Hello Eric and thank you for responding. Lets get down to the gritty.
You ask "For what?". I thought that was self evident. Since Mr. Lachot was kind enough to elude to the use of this theorem as the mathamatical basis for the design(spacing/slat width?)of this socalled Diffabsorber, I was, as usual, only trying to learn HOW this math was applied. If indeed the math is responsible for the performance of this device application, then why is it so difficult to understand my motive? :? Afterall, YOU've spent years of your own life doing the same thing...ie...trying to learn. :roll:


As to:
You are not triggered here by any experience you have

DUH!! How could I have had any experience when I don't even understand how the design is manifested by virtue of the math. :bang Second, how in the heck do you know what triggers me. I'll admit the "Chinese remainder theorem" caught my attention ....no different than the Quadradic Residue sequence caught my attention some 20
years ago...which seems to be a no brainer...after all...isn't that the WHOLE POINT of the QRD..Calculator. Hmmmm, either I or you seem to be missing something here. :roll: Speaking of complicated, I seem to remember a whole thread devoted to the mathamatics of the "curve" of Polys...actually, more than one. :roll: Second, who are YOU to render my interests as "complicated"? If anything, designing a room suspended on springs to decouple it at 20hz/100db says more about you than me. So WHO likes "complicated".........hmmmmm?


Firs off - there is nothing random about the spacing of those boards............. what makes it appear random is the multiple board widths - but the use of a 1x4 1x6 1x8 pattern (using the same slot width) yield the same results as using all 1x6 members - which would (of course) make it appear less random.
...
So, if I understand you correctly, the pattern of spacing is simply the result of using the same nominal sizes of lumber for the open areas. No math. No sequence. Just arbitrary placement of nominal sized boards, with adjacent spaces placed arbitrarily, although using the same nominal widths? IF, that is correct, then that is EXACTLY what I meant as "random"...otherwise it would appear that some sort of sequence would have been visually evident had some mathamatical "theorem" had been applied to the slat/slot placement sequence, no? So, if I understand, your design is NOT the same, nor uses the same design criteria, as Mr. Lachot, no?...in otherwords..you did NOT use this "Chinese remainder theorem" via Cox/Diantonio's paper. Is that correct?

There is definitely something going on "behind the scenes" it's absolutely my own design
Well, I guess that answers both questions. :mrgreen:

completely different from Tony Bonjovi's design for Power Station
Oh, that hadn't even entered my mind. But now that I think about it...ok.
What was HIS design based on? Some kind of chaos theorem?:lol: (just kidding Rod)

and I do not put it out for public review - sorry I can't help you there............

Ok, I respect that Rod. But I'm curious..., and please Rod, this is with all due respect......
if these designs, either yours, Cox/D../Mr. Lachot/ Tony Bonjovis's, John Sayers..or whoever's designs, haven't actually been tested in a lab(or have they?), may I ask how you or anyone else who uses SELF designed device designs, CERTIFY these actually do what you claim? :? Afterall, even Mr. Desart seems to still have questions(about a LOT of this stuff)..or am I missing something? I understand you test the actual room, but arn't these "test results" base on whole room performance, not device specific...just like measuring a given room response with Superchunks, broadband absorption, QRD's, Polys, etc already in place, will NOT tell you how any given device is performing, no? Vs RPG lab tests of specific devices as an example. Would not your application(especially with "behind the scenes" elements) be considered a "device"?

Please remember Rod, I am only trying to learn...just like you.

Thank you for your replys gentleman. And also remember..this is with ALL DUE RESPECT.
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Re: Small program for QRD diffusers (1D & 2D)

Postby homestudiobldr » Sat May 22, 2010 5:59 am

Actually, after reading this, visiting the ASC factory, talking to Art, and reading everything here for as long as this bbs has been here....I'm really beginning to wonder about some things. :roll:


http://www.acousticsciences.com/article ... of-qsf.pdf
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Re: Small program for QRD diffusers (1D & 2D)

Postby Eric.Desart » Sat May 22, 2010 10:09 am

tonio wrote:Going by the animations, use of poly (or diffusers in general ) on a boundary is not preferred? Why do so many studios have QRD's on the rear wall?

Tonio. A QRD is a device on its own. A poly is in fact part a reflector, part a diffuser depending on wavelength.
What you did is OK. Its not because some things can be improved that all the rest is bad.

To have a perfect reflector you poly size should be ca 1/2 wavelength. If your wavelength becomes smaller it will start listening to this rounded shape of this poly. For larger wavelengths you must see this as a front where this wave will scatter/diffract around these edges as shown in the animation as I pointed Rod to.
http://www.acoustics.salford.ac.uk/fesc ... ffract.htm
To get this kind of scattering imagine that that wave wants to follow its path. But part of this front is blocked by the diffuser and the rest can continue. In fact you get a reflective boundary neighboring an emptiness. If that part next to that poly is as well reflective by mounting it on a wall, that additional free effect is largely lost.
This can as well be an empty depth, or absorption. The basic idea is that the difference in impedance of these neighboring surfaces cause these phenomena. And logically this is frequency dependent. A poly on a wall will be +/- seen for large wave fronts as a continuing reflective surface. And leaving a gap then between poly and wall of 1 inch will hardly be felt or seen by that wave front.

Look how they apply diffusers in reverberation rooms.
Image
source: http://www.ibp.fraunhofer.de/akustik/la ... llraum.JPG
Now...., you don't have to go that far of course.

Just to give you an idea: You know how they tune such a room? How do they know they have enough diffusers using this mounting method?
Well, there is a relationship between the absorption of a to be measured sample and the diffusivity of the room. The higher the diffusivity the higher the absorption will become.
Now there are 2 things:

  1. One wants to keep the reverb time of the room as high as possible, to make sure that the difference between the empty room and the room with sample remains as large as possible to optimize measurement accuracy.
    But here is a problem: Also these diffusers, no matter their quality and reflective properties will absorb somewhat. That is then also the reason that standards describe a minimum mass per surface unit to ensure that these diffusers are as stable as possible and having a high enough insulation value (related to vibration level) to minimize that absorption.
    For the traditional cutoff range of a lab down to the lower cutoff of the 100 Hz 1/3 octave band that is >= 5kg/m² equaling +/- 1.024 psf. But for lower frequencies this number should be increased (but also the sizes/surface in lots of cases should be increased). Always be aware that whatever is described in standards is related to the frequency range the standard is designed for.
    Hence: basically the less added diffusers the better.
     
  2. But this contradicts with the need for more diffusers in order to maximize diffusivity.
So how does one find this balance? At one hand minimizing the number of diffusers to minimize absorption, at the other hand having enough diffusers to make the room as diffuse as possible?
Here this relationship between absorption and diffusion comes into the picture.
 
  1. One puts a standard good absorption sample (as glassfiber) with the quantity and surface ratio as described by the standard. In fact what is referred to as the standard A mount.
     
  2. One measures the absorption.
     
  3. By adding diffusers, and remeasuring that same sample (versus the new empty room including these added diffusers), the absorption coefficient of that sample increases (hence it's as if that material becomes better).
    At a certain moment adding more diffusers will not increase the absorption of that sample any further, but will only lower the reverberation time of that empty room, which is to be avoided to preserve an as high as possible reverb time in the room.
    Hence by reading this it should be clear that, compared to real live circumstances, lab values are fucked up absorption values, since that room is really tuned to show the highest possible values (based on this A-mount calibration).
    One could assume that it should be preferable to measure some more moderate (practical use) values, but such a calibration procedure is a necessity to optimize and maintain compatibility between measurements and labs.
     
  4. Now this isn't just a question of adding diffusers in function of quantity/surface, but also finding the best position, angle, whatever, where and how they have the highest efficiency. Hence what you see in a reverb room is this balance showing the least numbers of diffusers resulting in the highest absorption of the calibration absorption sample.
    Here is some flexibility of course since there are other tests to take into account also, and labs want some more flexibility in function of non-standard testing as well.
Roughly you can say what you see in a lab is +/- the most efficient manner to apply diffusion (for such circumstances) with a minimum amount of diffusers.
:twisted: They of course have the advantage that they don't have to take the WAF factor into acount (Wife Acceptance Factor).
One can NOT use RPGs in such a lab, since they are too limited in the low frequency range (unless making monster-units) and showing significant too high (and non-linear) absorption.
Therefore also a company like RPG itself, having its own reverberation room, uses this kind free-hanging polys in their facility.
That makes it a bit stupid, that some people will describe polys as some kind of ordinary looking substandard DIY units (mainly meant for these poor guys not knowing better), while official measurement facilities use them worldwide and have to tune and calibrate their rooms with them in order to comply with standards requirements.

Some labs will use too lightweight diffusers (mass per surface unit) which translates in a lower empty room reverb time and lesser accuracy, certainly when low absorption values are to be measured. This phenomenon shows itself mainly in, and towards the lows.

EDIT: For the maniacs with math. Accidentally I found an interesting document related with the acoustic field in a Reverb Room. I put it here as well for others to break there teeth on ( :mrgreen: and in order not to loose this link - I'm not so altruistic, just like to give that impression):
THE SOUND FIELD IN A REVERBERATION ROOM (.pdf 41 pages)
Finn Jacobsen
Acoustic Technology, Department of Electrical Engineering
Technical University of Denmark, Building 352
Ørsteds Plads, DK-2800 Lyngby
Denmark
http://server.elektro.dtu.dk/ftp/fja/Room_acoustics.pdf
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Re: Small program for QRD diffusers (1D & 2D)

Postby Eric.Desart » Sat May 22, 2010 10:35 am


Such qsf, or any other comparable device, are inefficient devices when positioned free in space in function of the lows.
I'm hardly interested in related nice sounding stories. I know of enough measurements showing the effect of 3D objects free in space.
When you put them in corners or in front of a wall, they profit from the soundfield there in the same manner that glassfiber boards do.
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Re: Small program for QRD diffusers (1D & 2D)

Postby Bob » Sat May 22, 2010 6:01 pm

Eric.Desart wrote:

Such qsf, or any other comparable device, are inefficient devices when positioned free in space in function of the lows.

The Quick Sound Field is mentioned in "The Master Handbook Of Accoustics, 4th edition" pages 469 to 471.
It talks about fiddling with the ETC (energy time curve). Figure 23.7 shows a frequency graph from 100hz to 10000hz (with no prominent room modal resonances), which is quaint but a before/after graph would have been better. And talks about how a vocal recording room with QSFs, moving the microphone made no difference between recordings.

[Bob: posesser of two dozen books, reader of some]
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Re: Small program for QRD diffusers (1D & 2D)

Postby Bob » Sat May 22, 2010 6:23 pm


There was a concert hall in Toronto (Ontario Canada) that was designed "by accoustical experts" to have great accoustics according to the marketing/advertising, and was panned/hated at the opening night. For the next night, they hung from the ceiling about twenty five, 5' diameter, flat (not polys), circular sheets of plexyglass (hanging sound reflectors) at semi-random angles over the stage and a bit into the audience, and it made a huge difference.
I think it may have been Roy Tompson Hall, and a few years later they really made changes (details here), altering the interior shape by introducing 135,000 cubic feet of wood bulkheads and other things (reducing the volume by 13.5%), added two big adjustable acoustic canopies, retractable sound absorbent banners, moved a bunch of seats, made the stage floor more resonant, changed the floor carpeting to wood (remember the original was designed "by acoustical experts"), reduced HVAC noise. And they haven't fiddled with it since.
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Re: Small program for QRD diffusers (1D & 2D)

Postby Eric.Desart » Sun May 23, 2010 5:24 am

Bob wrote:[Bob: posesser of two dozen books, reader of some]

:mrgreen: :mrgreen: :mrgreen:

Without checking your reference now, and something which should be checkable in the forum here (which I told years ago in the former Yahoo forum).

I do admire Everest and think that the "Master Handbook of Acoustics" is a very valuable and readable book.
I still do have edition 2 of that book (printed edition) (also 4 & 5 electronic). I'm still searching for ed. 3 (just for the fun of it) and wonder how edition 1 looked like.
:twisted: When I first read that book (ed.2) long ago, with my background in physical, environmental, building and mainly industrial acoustics, and saw some of these pictures and pages (mainly related to these room acoustical applications), I rechecked the title to make sure I was still reading a book about acoustics.

That ed. 4 I specially bought to check a reference used by E. Winer at SOS (long ago) which he used as proof while I was sure Ethan used it out of context. Hence while I originally never intended to buy these later editions (after that ed. 2), one needs them since it is one of the most referred books in studio related fora. Now I try to get the complete collection ..... (some loose screws in my head).
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Re: Small program for QRD diffusers (1D & 2D)

Postby Rod Gervais » Sun May 23, 2010 4:23 pm

homestudiobldr wrote: So, if I understand you correctly, the pattern of spacing is simply the result of using the same nominal sizes of lumber for the open areas. No math. No sequence. Just arbitrary placement of nominal sized boards, with adjacent spaces placed arbitrarily, although using the same nominal widths? IF, that is correct, then that is EXACTLY what I meant as "random"...otherwise it would appear that some sort of sequence would have been visually evident had some mathamatical "theorem" had been applied to the slat/slot placement sequence, no? So, if I understand, your design is NOT the same, nor uses the same design criteria, as Mr. Lachot, no?...in otherwords..you did NOT use this "Chinese remainder theorem" via Cox/Diantonio's paper. Is that correct?


Apparently you don't understand me correctly - when i said there is nothing random - I meant exactly what I said - there is nothing random......... there is nothing arbitrary about the board placement - the slots are the widths I specify - and I have some very exacting tolerances when it comes to board spacing (which is another reason Power Station New England did not need to be tuned after the studio construction was completed - Tony's design was perfect - BUT - his lack of knowledge and control of the construction process was NOT). I have been known (and hated) because I have forced carpenters to tear down entire walls of finishes because they were outside of tolerance..... in this I stand outside of (and disagree with) the paper that suggests perhaps it would be better to throw away the ruler and let the slots vary - under those conditions I would find it very difficult to control room sound........

The spacing is anything but random - what i said (exactly) was that when using slats of various widths, there was (perhaps) the appearance of a random pattern, which is a differently colored horse......... and also that the total ratio of slat surface to slot surface is the same with my pattern as if you were using all 1x6....... although Eric did raise an interesting point in that regards as well (thanks Eric).

My design is not the same design as Wes uses - and no, I do not use the Chinese Remainder Theorem in my calculations (there is more than one way to skin a cat, or even that proverbial horse of a different color).

Ok, I respect that Rod. But I'm curious..., and please Rod, this is with all due respect......
if these designs, either yours, Cox/D../Mr. Lachot/ Tony Bonjovis's, John Sayers..or whoever's designs, haven't actually been tested in a lab(or have they?), may I ask how you or anyone else who uses SELF designed device designs, CERTIFY these actually do what you claim? :? Afterall, even Mr. Desart seems to still have questions(about a LOT of this stuff)..or am I missing something? I understand you test the actual room, but arn't these "test results" base on whole room performance, not device specific...just like measuring a given room response with Superchunks, broadband absorption, QRD's, Polys, etc already in place, will NOT tell you how any given device is performing, no? Vs RPG lab tests of specific devices as an example. Would not your application(especially with "behind the scenes" elements) be considered a "device"?


This is where you are getting confused by things - and I will try to explain......... I am not making a single claim about any self designed devices.

We are designing rooms here - not individual devices.......... Remember that I said I was aware that Eric's design (using the polys) was not an afterthought - but rather a part of the whole room's design........ well that is true for Eric, John, Wes, Tony, Russ Berger, actually there is a pretty long list - and I think I fit somewhere in it.........

These are all parts of a complete room design - not a room treatment - no one can construct a complete studio to test before they release the design to their clients - and that is what makes it difficult to explain........... and also why I will not divulge my exact construction.

Eric has a pretty good idea what is going on behind the scenes in my rooms - - not surprising, he's a pretty brilliant person - but even he doesn't know the exact details - and will never figure it out just by looking.

I know that we all have things going on outside of the view of the finished product that you see - and (with the exception of Tony's "A" room at Power Station - where I had a chance to get into his head and understand his design in it's entirety and was able to actually improve the room when we built the 2nd one) no one is sharing EXACTLY how they went, to get from "A" to "B"

Wes (who is a close personal friend of mine) is not sharing with me everything that is happening in his rooms and the exact construction details....... Nor has Eric shared exactly everything related to his design at Galaxy , and I consider him a close friend as well...........

Not only do I have a responsibility to my clients - I also have to make a living............ the design field is a fairly competitive one - and the current economy isn't exactly helping matters - and there are new "acousticians" popping up providing studio design and offering to solve problems with rooms that are not acoustically "cutting it"at an alarming rate (It's amazing to me the number of people I find in forums that have actually contracted work in the field who are searching for answers - obviously do not have a clue of what they are doing - but are being paid by someone who apparently thinks they are what they actually are not)......... I am in competition with these people, trying to put bread on my table and pay my bills..........

Generalizations and conversations about the concepts used are one thing - providing exact details are another..........

If I were selling a product to the general public - for them to purchase and place in their rooms, then testing the products and producing the results of those tests to the public, would be very important - although it still might not answer your question - which is how is it made and why does it work - but at least then you could purchase it, take it apart - examine and reverse engineer it - and duplicate the product on your own. But a complete studio is a different story.

It would be pretty expensive to buy Galaxy - or Avalon Studios (formerly Power Station New York) or even one of my client's studios to do the same.........

When Tony owned Power Station NY, he used to have people who represented major labels visit his facility, quite often some of the top engineers working for those labels, he was always happy to give them the grand tour............ and was always laughing after they left because he knew they were fishing to figure out how the rooms worked - and that they would never be able to do it by just looking at the finished product.

Every now and then I stop in and visit at Power Station New England- and have been there when engineers were having discussions on how the rooms worked - and laughed quietly to myself as I listened.

Please remember Rod, I am only trying to learn...just like you.


I understand this - all of us are leaning and striving to learn each and every day - that includes Eric - but you are asking something that I am not capable of providing - especially seeing as each and every room that i design is different from the rest - so it's a moving target you are trying to understand..........
Last edited by Rod Gervais on Sun May 23, 2010 8:15 pm, edited 1 time in total.
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Re: Small program for QRD diffusers (1D & 2D)

Postby bert stoltenborg » Sun May 23, 2010 6:04 pm

I also want to be smart and creative, and invent stuff and not tell ya all how I did it and then feel good about me.
:mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen:
If you view life with the knowledge that there are no problems, only opportunities, you are a marketing manager.......this is my personal philosophy
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Re: Small program for QRD diffusers (1D & 2D)

Postby Scott R. Foster » Sun May 23, 2010 6:55 pm

shut up hippy!
SRF
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Re: Small program for QRD diffusers (1D & 2D)

Postby Rod Gervais » Sun May 23, 2010 7:00 pm

LOL............ yeah Bert, what he said............. :wink:
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Re: Small program for QRD diffusers (1D & 2D)

Postby homestudiobldr » Sun May 23, 2010 7:31 pm

Hello Rod. Thank you. Nuff said. You are a gentleman. Carry on. :mrgreen:
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Re: Small program for QRD diffusers (1D & 2D)

Postby Eric.Desart » Sun May 23, 2010 7:39 pm

bert stoltenborg wrote:I also want to be smart and creative, and invent stuff and not tell ya all how I did it and then feel good about me.
:mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen: :mrgreen:

Scott R. Foster wrote:shut up hippy!

:twisted: Yep Bert, you really need to find another strategy ........
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Re: Small program for QRD diffusers (1D & 2D)

Postby tonio » Mon May 24, 2010 12:11 am

Eric.Desart wrote:
tonio wrote:Going by the animations, use of poly (or diffusers in general ) on a boundary is not preferred? Why do so many studios have QRD's on the rear wall?

Tonio. A QRD is a device on its own. A poly is in fact part a reflector, part a diffuser depending on wavelength.
What you did is OK. Its not because some things can be improved that all the rest is bad.

To have a perfect reflector you poly size should be ca 1/2 wavelength. If your wavelength becomes smaller it will start listening to this rounded shape of this poly. For larger wavelengths you must see this as a front where this wave will scatter/diffract around these edges as shown in the animation as I pointed Rod to.
http://www.acoustics.salford.ac.uk/fesc ... ffract.htm
To get this kind of scattering imagine that that wave wants to follow its path. But part of this front is blocked by the diffuser and the rest can continue. In fact you get a reflective boundary neighboring an emptiness. If that part next to that poly is as well reflective by mounting it on a wall, that additional free effect is largely lost.
This can as well be an empty depth, or absorption. The basic idea is that the difference in impedance of these neighboring surfaces cause these phenomena. And logically this is frequency dependent. A poly on a wall will be +/- seen for large wave fronts as a continuing reflective surface. And leaving a gap then between poly and wall of 1 inch will hardly be felt or seen by that wave front.

Look how they apply diffusers in reverberation rooms.
Image
source: http://www.ibp.fraunhofer.de/akustik/la ... llraum.JPG
Now...., you don't have to go that far of course.

Just to give you an idea: You know how they tune such a room? How do they know they have enough diffusers using this mounting method?
Well, there is a relationship between the absorption of a to be measured sample and the diffusivity of the room. The higher the diffusivity the higher the absorption will become.
Now there are 2 things:

  1. One wants to keep the reverb time of the room as high as possible, to make sure that the difference between the empty room and the room with sample remains as large as possible to optimize measurement accuracy.
    But here is a problem: Also these diffusers, no matter their quality and reflective properties will absorb somewhat. That is then also the reason that standards describe a minimum mass per surface unit to ensure that these diffusers are as stable as possible and having a high enough insulation value (related to vibration level) to minimize that absorption.
    For the traditional cutoff range of a lab down to the lower cutoff of the 100 Hz 1/3 octave band that is >= 5kg/m² equaling +/- 1.024 psf. But for lower frequencies this number should be increased (but also the sizes/surface in lots of cases should be increased). Always be aware that whatever is described in standards is related to the frequency range the standard is designed for.
    Hence: basically the less added diffusers the better.
     
  2. But this contradicts with the need for more diffusers in order to maximize diffusivity.
So how does one find this balance? At one hand minimizing the number of diffusers to minimize absorption, at the other hand having enough diffusers to make the room as diffuse as possible?
Here this relationship between absorption and diffusion comes into the picture.
 
  1. One puts a standard good absorption sample (as glassfiber) with the quantity and surface ratio as described by the standard. In fact what is referred to as the standard A mount.
     
  2. One measures the absorption.
     
  3. By adding diffusers, and remeasuring that same sample (versus the new empty room including these added diffusers), the absorption coefficient of that sample increases (hence it's as if that material becomes better).
    At a certain moment adding more diffusers will not increase the absorption of that sample any further, but will only lower the reverberation time of that empty room, which is to be avoided to preserve an as high as possible reverb time in the room.
    Hence by reading this it should be clear that, compared to real live circumstances, lab values are fucked up absorption values, since that room is really tuned to show the highest possible values (based on this A-mount calibration).
    One could assume that it should be preferable to measure some more moderate (practical use) values, but such a calibration procedure is a necessity to optimize and maintain compatibility between measurements and labs.
     
  4. Now this isn't just a question of adding diffusers in function of quantity/surface, but also finding the best position, angle, whatever, where and how they have the highest efficiency. Hence what you see in a reverb room is this balance showing the least numbers of diffusers resulting in the highest absorption of the calibration absorption sample.
    Here is some flexibility of course since there are other tests to take into account also, and labs want some more flexibility in function of non-standard testing as well.
Roughly you can say what you see in a lab is +/- the most efficient manner to apply diffusion (for such circumstances) with a minimum amount of diffusers.
:twisted: They of course have the advantage that they don't have to take the WAF factor into acount (Wife Acceptance Factor).
One can NOT use RPGs in such a lab, since they are too limited in the low frequency range (unless making monster-units) and showing significant too high (and non-linear) absorption.
Therefore also a company like RPG itself, having its own reverberation room, uses this kind free-hanging polys in their facility.
That makes it a bit stupid, that some people will describe polys as some kind of ordinary looking substandard DIY units (mainly meant for these poor guys not knowing better), while official measurement facilities use them worldwide and have to tune and calibrate their rooms with them in order to comply with standards requirements.

Some labs will use too lightweight diffusers (mass per surface unit) which translates in a lower empty room reverb time and lesser accuracy, certainly when low absorption values are to be measured. This phenomenon shows itself mainly in, and towards the lows.

EDIT: For the maniacs with math. Accidentally I found an interesting document related with the acoustic field in a Reverb Room. I put it here as well for others to break there teeth on ( :mrgreen: and in order not to loose this link - I'm not so altruistic, just like to give that impression):
THE SOUND FIELD IN A REVERBERATION ROOM (.pdf 41 pages)
Finn Jacobsen
Acoustic Technology, Department of Electrical Engineering
Technical University of Denmark, Building 352
Ørsteds Plads, DK-2800 Lyngby
Denmark
http://server.elektro.dtu.dk/ftp/fja/Room_acoustics.pdf


Eric, Thank you!!
I would comment more, however I am in splint (right hand fingers and lacerated resulting in 12 stitches).

T
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Re: Small program for QRD diffusers (1D & 2D)

Postby homestudiobldr » Tue May 25, 2010 4:17 am

Dear Rod. With all due respect, I submit, you should change the title of the next issue of your book to........

Home Studios, Build it like the Pros, with a caveat, you can't. Cause they won't REALLY tell you the secrets of the PRO's. It's proprietary"
homestudiobldr
 
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Re: Small program for QRD diffusers (1D & 2D)

Postby Eric.Desart » Tue May 25, 2010 11:12 am

homestudiobldr wrote:Dear Rod. With all due respect, I submit, you should change the title of the next issue of your book to........
Home Studios, Build it like the Pros, with a caveat, you can't. Cause they won't REALLY tell you the secrets of the PRO's. It's proprietary"

:bang
You can buy more books. One goes more in depth in math, other more in constructional calculations, you can learn more about acoustics of which numerous books exist, and lots of practical experience is a matter of feeling build up over many years.

You can write a book about painting, recording, whatever. You can explain techniques. Experience can't be always expressed in words.

And further you pay a book for what's in it without giving you any right to what's NOT in it. And a book is written for a specific audience. ANY book.
What you can expect from a book that what is written is correct.

What you're looking for is a guideline: "How to copy a professional studio, of the best studios designed by the best, most educated, professional designers?"
That book should cost a hundredfold (in as far it's even possible to write such a book) as you can easily see when checking prices of books targeted to a specific more limited Pro-audience.
Jonathan here follows a PhD in acoustics now. You maybe can follow his example?

To know the speed of sound in air you can buy this book: http://www.elsevier.com/wps/find/bookde ... escription
It costs USD 1471. About 300 pages (of ca 1000) are specific dedicated to calculate the speed of sound in air.
You can also check Wikipedia ..... for free. The difference is that in the book you can find all influencing chemical and vibrational components of which air is composed, and some history of sound speed calculations and their physical context.
And just to read it you must have a rather solid base of chemistry, physics and math.
In Everest you find a very simple stylized formula.
So ...... when is a book complete? Maybe you can buy the book Formulas of acoustics by Professor Fridolin P. Mechel ? Costs only € 296. There is a second edition from 2008 (1276 pages, one formula after the other).

Helmholtz slat/slot resonators: You find simple formulas. You can also learn BEM and/or FEM (Finite Elements Method).
Jonathan's spreadsheet to calculate panel dampers: It's a VERY nice and good spreadsheet (and with references and a special note of thanks to Terry here). But Jonathan writes that it's best to keep some possibilities to tune them to the real live resonance frequency.
You once made yourself angry to me that these slat/slot resonators formulas didn't cover all these possible influences, while I just wanted to point out that all these formulas are based on stylized boundary conditions.

What you're looking for are things to copy without understanding.
You made yourself very nervous that nobody could give you the exact formulas to calculate the edge effect on the absorption of these diamond patterns you designed for absorbers on a wall.
You told you want to understand and learn. Well tell what you read already about this edge-effect, it's question marks and uncertainties?
What you did was making yourself angry to me when I warned people about some so-called expert, by his total lack of related insight, spread related misleading information on the net (clearly to substantiate a point to his commercial benefit). And in this case my comments were even substantiated and supported by related footnotes and comments in the related official standard itself.
Image
divinely-inspired
Eric.Desart
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Re: Small program for QRD diffusers (1D & 2D)

Postby Scott R. Foster » Tue May 25, 2010 12:56 pm

Homes likes to play a game that consists of asking clever questions and then rejecting any answer that is complicated - instead insisting that any question in physics actually has a superbly simple answer which "experts" hide from him. He likes to post lots of links to disparate answers to a given question as proof of this theory[there is an especial affinity to wrong answers in this process]. When this proposition fails to hold water as discussion unfolds, Homes accuses everyone who actually does understand the phenomena of being some sort of a con artist who has stolen the answer. It reminds me of the guys who are convinced you can make your car run on water instead of gasoline - but "big oil" is hiding the secret to the process. It must be very frustrating for Homes to perceive physics in this fashion and I suppose this explains why he so often comes across as angry.

This is can also be very annoying for others if they fall into the trap of taking Homes' views on physics seriously.

Despite the annoyance suffered by many, in my view, Homes serves a valid purpose here at StudioTips in that he asks good questions that lead to interesting discussions - for this reason I always enjoy his posts. I don't read them of course, but I do enjoy reading the points raised when people more informed than I answer his questions. Thus the process is quite useful as long as no one gets bogged down in the matter of getting Homes to accept the answers his questions engender.

My $0.02
SRF
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Re: Small program for QRD diffusers (1D & 2D)

Postby Rod Gervais » Tue May 25, 2010 2:27 pm

homestudiobldr wrote:Hello Rod. Thank you. Nuff said. You are a gentleman. Carry on. :mrgreen:


homestudiobldr wrote:Dear Rod. With all due respect, I submit, you should change the title of the next issue of your book to........

Home Studios, Build it like the Pros, with a caveat, you can't. Cause they won't REALLY tell you the secrets of the PRO's. It's proprietary"


Well which is it? Am I the gentleman or the scourge of the earth?

Lol............

You ask how i design the "devices" I use - and I take the tome to explain to you that the entire room is the "device" - and that each room is different - thus each room is designed differently. If you were to look at the differences in the control rooms i have designed for clients you would see what I mean..........

I then go on to explain to you that I am not doing what you suggest - selling to the public something which I will not explain - I am not in the business of designing and selling room treatments........

So you then then you throw me a respectful understanding before tossing me a dis......... :bang :bang

The book apparently has some small value to some - there are studio designers and builders who provide it to their clients to help them understand what challenges they are facing (both from a design and construction point of view)-and so that their clients might better understand the associated costs.

It sits available in over 140 University libraries world wide - and it leads a DIY home studio enthusiast through the steps they can take to build a good if not great home studio......... I spent an entire year of my life putting it together - but would spend a lifetime trying to explain each and every possibility to create a whole room package..........

Also, setting all of that aside - when I was contacted by my publisher to see if I would be interested in authoring a book for them - they were very specific what they wanted - what the intended audience was and how they wanted it put together - I assured them that I could accomplish this and completely understood the criteria - and they are very happy with the results.

What I would suggest (to you) is that you invest the time. effort and money that I have invested in the more than 30 years I have been in this industry - and after that you will (perhaps) have all of my knowledge - you can then write your own book and reveal all of the "secrets" hidden behind the scenes......... :wink:

Sincerely,

Rod
Rod

If you view life with the knowledge that there are no problems, only opportunities, you will find the load to be a lot lighter then it might be otherwise......... this is my personal philosophy
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Re: Small program for QRD diffusers (1D & 2D)

Postby Bob » Tue May 25, 2010 3:59 pm

My take on homestudiobldr's post was a little different than Scott's, Eric's, or Rod's.
I've seen some really effective letters lately. Letters that inspire the recipient to strive beyond endurance to fulfill the expectation, the request, and the need. homestudiobldr's post was pretty much an example of how not to write such a letter. Quite ignorable.

Rod Gervais wrote:The book apparently has some small value to some
Modesty. The book records your valuable construction experience into a how to get it right, or at least pretty good, the first time. A "this is what it takes", or "I've seen homeowners do things like this and be happy".

Rod Gervais wrote:Am I the gentleman or the scourge of the earth?

[humor]

Star Trek Philosophy 101

a) "the Kurlan civilisation believed that an individual was a community of individuals. Inside us are many voices, each with its own desires, its own style, its own view of the world." (Star Trek TNG, "The Chase")
so maybe you're both, and a dozen others.

b) Edith Keeler was a wonderful, caring, lady. And because of that she was also the scourge of the earth. (Star Trek TOS, "The City on the Edge of Forever").

[/humor]
Bob
 
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