Distribution of sound deadening diffusors

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etheory

etheory

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Sydney, Australia
Shameless reposting a link that Jeff put on FB:
4927197753_1ea3216e8f1.jpg


This is Studio C at Blackbird Studios in http://www.blackbirdstudio.com/#/home/

This is the most widespread use of such a surface I've seen, not that I go to many actual studios....

Does anyone know what the relevance of the heights in the pattern is?

Are they totally random? Stochastically random? Quasi-random? Halton points? Hammersely points? Perlin Noise? None of the above?

I'm quite curious. My full-time job is writing physically-based rendering software and I spend a lot of my time studying these types of patterns. I'm curious if there are any other mathematicians in the house that might be able to shed some light on the physics behind which patterns give the best absorption.

Does anyone have a story about a before and after of installation of a large surface area of these? If so, are they really THAT good?

thanks!
 
A friend of mine (Ethan Winer) sells sound treatments for studio/recording spaces http://www.realtraps.com/and recently wrote a book, that covers this "acoustic treatment" (broadly) if not answers your specific question. http://www.ethanwiner.com/book.htm He is not a poster here, but active on several audio/recording forums. So to get an answer from him you probably need to ask on one of those forums.

If I understand your question, are you asking about the different heights in the small local patterns? My understanding is this is to break up the simple wavefront reflection that would occur from bouncing off a flat surface. Further the different height regions trap/diffuse the nearby reflections from deeper surfaces.  Even a perfectly incident sound, that bounces straight back, will get the wavefront scrambled by the different depths of the reflecting surfaces.

In deadening an acoustic space you mainly want to prevent standing waves between flat surfaces.

or not....

JR
 
My understanding of acoustical concepts is much less than some people, but I am under the impression that a random construction would not do much good. The walls of Studio C use a primitive root sequence. The ceiling is a fractal diffuser--I'm not sure of the construction, but it also looks like blocks of 2D primitive root diffusers (meaning the sequence is extended along two axes, though in three dimensions) arranged to form one giant 2D PRD across the whole ceiling. It's quite deep (bottom effective frequency is determined by depth); I remember reading that the room diffuses (not absorbs!) effectively down to 50 Hz or something crazy.

There is a good PRD calculator on the net. Edit: found it. http://www.oliverprime.com/prd/

Dylan
 
My experience with  " those more popular " ones sold  [ that are very even and look like a patterns ]
is that they do break up the energy but almost create greater pockets of energy close to them and then just a mushy
field farther until nothing . This is in a smaller live performance hall , where I think the architect choose them for looks
A friend made some for his smallish drum room at about 20 % coverage , they seemed pleasant .
 
This is called Quadratic Residue Diffuser. It is complex math based on some Schroeder equations.
Basically sound waves hit this surface and in predicted way they break into many directions, diffuse, so acoustic energy in room is not killed by absorbers on walls but instead spread all around. That way there's no acoustic energy buildup due to early reflections and room modes, but this type of room treatment doesn't suck energy and leaves dull sounding space.
Maybe in this room is a bit over exaggerated amount of QRD... but looks cool... if you're not claustrophobic!

Here's an example of QRD calculator:
http://www.youtube.com/watch?v=BqC8ZDF2wCs

and it's free download!
http://www.subwoofer-builder.com/qrdude.htm
 
http://www.amazon.com/Acoustic-Absorbers-Diffusers-Theory-Application/dp/0415296498

I have this book.  it's great.  (As someone said above Blackbird Studio C is primitive root not QRD.)

As yet another person said diffusers do not "deaden" the sound.
 
Sorry for the minor hijack, but has GM moved out of that studio? I remember when it was touted as his resident studio. Just curious. I can't see him using some of the gear they have in the racks, nor the SSL.

It's a shame he no longer has a forum, otherwise you could ask him - the diffusers were specified by him.

J

btw - if you try a search, I believe GM did have an account here... No reason not to shoot him a PM... What's the worst that can happen?

Last active in 2005, alas: http://www.groupdiy.com/index.php?action=profile;u=405
 
If you are building a dedicated Listening Room or studio, one of the simplest and most important things you need to do is to ensure no 2 surfaces are parallel.

I discussed this with Julian Wright, Celestion and Prof Peter Lord, Salford over the years.  Peter suggested 2 degrees skew was sufficient.  In the 90's, when PAFEC developed the first usable acoustic Boundary Element, Julian confirmed this.

If you have parallel walls, you have to use a HUGE amount of absorption to obviate flutter echoes.  That includes stuff like QRD.

If you are not using hard stuff like QRD diffusors, you end up having so much absorption that your RT60s drops below your target.  Wonky walls give you much more freedom without having your room look like a set from Alien.

Don't ask me how I know this but I'm consoled by the fact that at least 3 other famous UK 'experts' purpose built Listening Rooms and got them wrong too.
 
> the best absorption.

Not absorption. Diffusion.

The sound energy does not go away, it is spread all over.

The classic diffusers are curved panels; also baroque and rococo embellishments in older concert halls.

> the heights in the pattern

The brand-answer is "RPG", founded by folks who studied this less-obvious way to diffuse sound, and practical implementations. Shot is right that the general idea is "QRD".

> Quasi-random?

My suspicion has always been that a random assortment of depths would give 80% of the effect of optimized QRD. If you have to cut stuff anyway, in this 21st century, may as well do the QRD math. But if you have a lot of leftover sticks or fire-wood, scatter it.

The fairly obvious physical-law trends apply. If the total depth high to low is only an inch, it can't affect bass. (However optimum QRD can diffuse tones lower than you'd think.) If it's all big chunks, treble will bounce with little scatter. (We had 6"x6" curbs on a wall and it bounced highs mostly like it was flat; but great places for picks, sticks, and bows.)

EDIT: I'll be danged. RPG has a picture of the hall I'm talking about. This is the pit, not the main stage. (The big panels in the distance are just 45 degree bouncers, specced by BBN before RPG came to fame.)

http://www.rpginc.com/images/featured/QRD7_MAIN.jpg
 
I think they lessen one problem but it's not like they create an  " accurate  " room
and you need a certain distance from them . look pretty though,  just another tool .
 
Balijon said:
Stacking irregular cut 'firewood' logs against a absorbent treated wall (like RockWool), can create very interesting diffusion / absorption wall sections and it is cheap to implement.  Make sure to 'tie-down' your logs well.
Click to expand...
One of the best diffusors is open bookshelfs .. with books.  If I was building a purposed domestic Listening / Music Room, I'd do the 2 degree wonky walls and turn it into a library. 

Its no coincidence that Music Rooms in old homes were often the Library too.  The ceiling is the most difficult surface to get wonky so put your QRD diffusors there disguised as crystal chandeliers.  That's cos its difficult to tread the floor.

But wonkiness is the easiest & best if you can do it.
 

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