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Question about a Diffusor specs... hoping Ethan might have some input Dynamics Plugins
Old 14th September 2011
  #1
Gear Head
 

Question about a Diffusor specs... hoping Ethan might have some input

Ethan, I'm considering building the diffusor for the back wall of a listening room... I see that the diffusor plans from this link have been executed successfully:

PME Records QRD Diffusor Construction

My question is: The design on that page calls for the wood blocks to be made of 2" X 2" sections of wood.

I'd like to make one out of cedar. I have access to 1" X 1"

Do you think the size of the wood blocs matters... could I get away with making it with 1"X1" sections of wood (which essentially would mean I would repeat the pattern of each line multiple times to make the diffusor the size I'd like)? I guess I could also go the extra length of buying 1"X2" section of wood and just gluing them together to make the 2X2...

Anyhow, just curious as to your response.

Thanks,

TS
Old 14th September 2011
  #2
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Jens Eklund's Avatar
Quote:
Originally Posted by soundoff View Post
Ethan, I'm considering building the diffusor for the back wall of a listening room... I see that the diffusor plans from this link have been executed successfully:

PME Records QRD Diffusor Construction

My question is: The design on that page calls for the wood blocks to be made of 2" X 2" sections of wood.

I'd like to make one out of cedar. I have access to 1" X 1"

Do you think the size of the wood blocs matters... could I get away with making it with 1"X1" sections of wood (which essentially would mean I would repeat the pattern of each line multiple times to make the diffusor the size I'd like)? I guess I could also go the extra length of buying 1"X2" section of wood and just gluing them together to make the 2X2...

Anyhow, just curious as to your response.

Thanks,

TS
All you need:

QRD diffusers: Technical Overview

Old 14th September 2011
  #3
Gear Head
 

Thanks for the link!

No quick short answer to my question?
Old 14th September 2011
  #4
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Ethan, I'm considering building the diffusor for the back wall of a listening room... I see that the diffusor plans from this link have been executed successfully:

PME Records QRD Diffusor Construction
I'm not Ethan but I will try to help.
Quote:
Originally Posted by soundoff View Post
My question is: The design on that page calls for the wood blocks to be made of 2" X 2" sections of wood.

I'd like to make one out of cedar. I have access to 1" X 1"

Do you think the size of the wood blocs matters... could I get away with making it with 1"X1" sections of wood (which essentially would mean I would repeat the pattern of each line multiple times to make the diffusor the size I'd like)? I guess I could also go the extra length of buying 1"X2" section of wood and just gluing them together to make the 2X2...
It's ok to use 1"x1" cedar. Maximum working frequency will be doubled because smaller dimensions of blocks.
If you need to repeat the pattern, use some pseudo-random binary sequence or coin flipping to change orientation (rotation) of each diffuser in your bigger construction. This will prevent a lobbing in radiation characteristic of bigger diffusor construction.
Old 14th September 2011
  #5
Gear Head
 

Thanks Boggy... appreciate the short-take.

I know that every room and and every room's acoustical issues are different... but is it necessarily bad to double the maximum working frequency? Speaking in general terms, of course
Old 14th September 2011
  #6
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Thanks Boggy... appreciate the short-take.

I know that every room and and every room's acoustical issues are different... but is it necessarily bad to double the maximum working frequency? Speaking in general terms, of course
It's not bad, really.
It's not easy to build 2D, then some people try to get a bigger diffusive surface with smaller effort and costs. 2"x2" seems to be cost/effort effective, then someone before you, decide to use it instead of thinner blocks... or because he has access to 2"x2" blocks... who knows? heh
Old 14th September 2011
  #7
Gear Head
 

Okay.

I was thinking 1X1 cedar because (a) I have access to it and (b) it's a lighter wood than pine.

Just for the sake of discussion: do the blocks of wood need to be symmetrical? 1X1 or 2X2, for instance? Could someone go with a 1x2???? Just curious if that would have an ill effect.
Old 14th September 2011
  #8
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Im looking into building a diffusser also. Any reason you chose the wood blocks design and not the square boxs or "lanes" of wood strips?

Not saying your design is bad, just wondering what makes one better then another
Old 14th September 2011
  #9
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Okay.

I was thinking 1X1 cedar because (a) I have access to it and (b) it's a lighter wood than pine.
I understand you. It's ok... diffusers may be really heavy sometimes.
Quote:
Originally Posted by soundoff View Post
Just for the sake of discussion: do the blocks of wood need to be symmetrical? 1X1 or 2X2, for instance?
Not really if you don't need to have same working frequency range horizontally and vertically...
At longer side you will have proportionally lower high working frequency than at shorter side. But diffusion will exist regardless of this.
Quote:
Originally Posted by soundoff View Post
Could someone go with a 1x2????
yes
Quote:
Originally Posted by soundoff View Post
Just curious if that would have an ill effect.
No ill effects...
Old 14th September 2011
  #10
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Quote:
Originally Posted by soundoff View Post
Ethan, I'm considering building the diffusor for the back wall of a listening room... I see that the diffusor plans from this link have been executed successfully:

PME Records QRD Diffusor Construction

My question is: The design on that page calls for the wood blocks to be made of 2" X 2" sections of wood.

I'd like to make one out of cedar. I have access to 1" X 1"

Do you think the size of the wood blocs matters... could I get away with making it with 1"X1" sections of wood (which essentially would mean I would repeat the pattern of each line multiple times to make the diffusor the size I'd like)? I guess I could also go the extra length of buying 1"X2" section of wood and just gluing them together to make the 2X2...

Anyhow, just curious as to your response.

Thanks,

TS
it should be noted that the diffuser in your link is the BBC PRD (PRD, not QRD). i can link to the .pdf when i am home...and that the BBC design is an array of smaller PRDs --- as you'll notice the PRD on that site is 12x12 which does not conform to PRD criteria. the BBC PRD also did not produce a measured null at normal incidence as would be predicted with PRDs (whether this is a design criteria for you or not...)

you may be better off designing your own 2D PRD (which will likely have greater bandwidth vs that of the BBC).

if this room is a listening room, is there a particular reason you require diffusion in 2planes (2D) vs that of 1D? the 1D QRD/PRDs (oriented with vertical wells to spatially disperse in the horizontal plane) may be more beneficial on the rear wall if you are interested in laterally arriving diffused returns...where-as the 2D will disperse precious energy to the floor and ceiling which may not be desired...
Old 14th September 2011
  #11
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Quote:
Originally Posted by JoRillo View Post
Im looking into building a diffusser also. Any reason you chose the wood blocks design and not the square boxs or "lanes" of wood strips?

Not saying your design is bad, just wondering what makes one better then another
the 2D in the original post disperses energy across 2 planes (eg, horizontal plane (both sidewalls) + vertical plane (floor/ceiling)), where-as the 1dimensional diffusers disperse in one plane.

it depends on the design criteria of the room and what the diffuser will be used for. generally in critical listening rooms or control rooms, 1D's will be used on the rear wall such that energy is dispersed horizontally (eg to the side walls, NOT vertically to the floor/ceiling) - because it is the lateral arriving diffused returns which are important for envelopment. a 2D will disperse less energy in the horizontal plane as now energy is also being dispersed to the floor/ceiling.

i think there is a first-assumption for many (myself included) that 2D is automatically 'better' - but then once you do some research you'll realize that in many cases, 1D is the way to go (depending on your design criteria).
Old 14th September 2011
  #12
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Jens Eklund's Avatar
Quote:
Originally Posted by localhost127 View Post
i think there is a first-assumption for many (myself included) that 2D is automatically 'better' - but then once you do some research you'll realize that in many cases, 1D is the way to go (depending on your design criteria).
+1

To all of those interested in diffuser design; install QRDude (free) or buy ”Reflex” (by AFMG) if accurate prediction model is required and 1D is sufficient.
Old 14th September 2011
  #13
Gear Head
 

The reason I chose it, is that my seating in my home theater is about 4 feet from the rear wall. I know this is not ideal, but it is what it is and it can't change. The wall is both dry wall and 2 large windows.

In Ethan Winer's Real Traps Diffusor video, he talks about diffusors being in appropriate for rooms where the seating is near the back wall... however he points out that these skyline diffusors are best if seating is near the diffusor (and shows an image from the skywalker studio where musicians are seated directly near skyline diffusors).

My idea, is to build a 6ft X 5ft skyline diffusor. It will be mounted on a board within a frame. The frame will have legs that support it from below and the to will have 2 points that will connected a chains to mounting hooks in the ceiling.

I will also add 2" 6pound insulation boards on the backside.

At any rate, the plans included on the link that I provided (I think!!!) have been used by others with success.

I'm definitely a do-it-yourselfer with limited acoustical knowledge, but I definitely get the feeling that I would be better off with some kind of diffusion on the back wall to help with known issues of sound bouncing off of back walls.

The skyline plans on the link that I provided are pretty straight-forward. The 1-D diffusors also look do-able. I haven't seen any solid plans for building one --- which, honestly, I would really need some solid plans.

Anyhow, that's where I'm coming from...



(I guess I should add... Ethan, in that same video, does say that another option would be to add some insulation panes on the back wall that are randomly covered by wood slats, as that would add some diffusion. Any thoughts?).
Old 14th September 2011
  #14
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
........
(I guess I should add... Ethan, in that same video, does say that another option would be to add some insulation panes on the back wall that are randomly covered by wood slats, as that would add some diffusion. Any thoughts?).
you can find info about binary diffusers here: DIY Binary Amplitude Diffuser anyone?
Old 14th September 2011
  #15
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Ethan Winer's Avatar
 

Lightbulb

Quote:
Originally Posted by soundoff View Post
Ethan, I'm considering building the diffusor for the back wall of a listening room... I see that the diffusor plans from this link have been executed successfully
I'm not as expert with diffusion as others here who are already answering, so I'll leave you in their good hands.

--Ethan
Old 14th September 2011
  #16
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Quote:
Originally Posted by soundoff View Post
The reason I chose it, is that my seating in my home theater is about 4 feet from the rear wall. I know this is not ideal, but it is what it is and it can't change. The wall is both dry wall and 2 large windows.

just fyi, the reason you do not want to sit directly against a diffuser is (like a multi-way speaker,) it takes some distance for the sound-field to develop.






Quote:
Originally Posted by soundoff View Post
My idea, is to build a 6ft X 5ft skyline diffusor. It will be mounted on a board within a frame. The frame will have legs that support it from below and the to will have 2 points that will connected a chains to mounting hooks in the ceiling.
if you are building a 6ft x 5ft diffuser, then you will want to design your own skyline vs the BBC PRD (which as i said above is not a single PRD but an array of many smaller order PRDs - hence why the dimensions are 12 wells x 12 wells).

there are PRD calculators out there as well as QRDude which can do 1D and 2D Quadratic Residue Diffusers.

Jens or others can correct me here, but if you are doing 2D PRD you would likely want to do 1 period of the largest prime that fits your physical dimensions, where if you were doing QRDs, you would want to design an array of multiple periods of a single QRD - utilizing inverse QRDs and applying the Barker Code for modulation.

first, you need to decide whether 1D or 2D fit your design criteria based on the function of your room.
Old 14th September 2011
  #17
Gear Addict
 

Quote:
however he points out that these skyline diffusors are best if seating is near the diffusor (and shows an image from the skywalker studio where musicians are seated directly near skyline diffusors).
I don`t think he says excactly that, just that it can be used close up intentionally to enhance the sound in some settings.

In the skywalker studio it was string a quartet (pretty much omni directional), and the microphone was further away, very different from a control/listening room.
It would not have worked with trumpets (high directivity).

another reason that diffusors can be pretty close to some instruments is that the music being created is not static or set when it comes to phrasing and timber of tone(unlike in a recording), there is an interaction between musicians/acoustics.

p.s personal prefferance (and others who have tried it), poly diffusors can be closer to listening position than qrd`s when listening to music, as long as they are not to wide,(mine are currently between 26cm and 46cm), have a good curve and are "free standing" and not in a huge array without spacing, using polys is of course another route.

For prd design, maybe Jens will chime in?

Last edited by hsal; 14th September 2011 at 07:49 PM.. Reason: pointing out width
Old 14th September 2011
  #18
Gear Head
 

Oh boy... I'm drowning!!! Man over board, Man over board!!!

I kind of assumed this would happen. I feel like this is all beginning to slip over my head!

I know the original post in this thread was somewhat novice in approach -- my basic issue is: aside from corner superchunk bass traps, my back wall in my HT is completely exposed. I'd rather not deaden it completely with traps - and, per the Real Traps diffusor video, it seems like I would benefit from some kind of diffusor.

I'm looking for something that is relatively easy to build and test. The skyline model looks relatively easy - or I should say, looked...

I'm wondering if some kind of slat/slot diffusor would be better?

Am I wrong in assuming that I could build a slat/slot diffusor by framing some plywood... adding some 705 or 703 on top... and then randomly placing vertical wood slats overtop of the acoustic insulation?

I've read through a couple of the threads that touch on slat diffusors. I hate to say it this way... but I need this stuff broken down a bit more. It's unclear to me (a) what target frequencies should be, (b) what widths of wood should be used, and (c) how to come up with a spacing pattern?

Is there a way to keep this relatively simple? Or am I assuming too much...
Old 14th September 2011
  #19
Gear Head
 

Quote:
Originally Posted by boggy View Post
you can find info about binary diffusers here: DIY Binary Amplitude Diffuser anyone?
Boggy, adding on to my post above... the link you provided has a binary sequence that you developed. I might been completely wrong about this but...in making a slat/slot diffusor... this binary sequence tells you the random order to place slats. In other words, could I say that each binary position = 1 inch? In other words, from left to right on a slat/slot diffusor, according to the binary sequence, the first 6 inches (positions 0-5) would have slats of wood... followed by a 1 inch slot (position 6)... followed by a 1 inch slat (position 7) and so on???

If the above is correct... would the slats in positions 0-5 be touching? Do you leave a slight gap (say 1/8th of an inch or so) between them???
Old 14th September 2011
  #20
Gear Addict
 

as Localhost posted , one of the main reasons having diffusors placed at the backwall is to scatter energy to the sides, it will then hit the sidewalls behind listening position, and be reflected back towards the listener.

The angle these diffuse reflections comes at is important from a psychoacoustic view, because the brain picks up the timing difference of when sounds arrive at each ear, and this creates a sensation of spaciousness.

You can use prd (skyline), but less sound will arrive from the side with this type of diffusor.

Personally I have not tried skylines at backwall, so I have no experience with this setup.

Slatts with mls pattern will scatter some sound, but not as evenly as qrd/prd, it will also have much less energy, due to the wall being hybrid, both dampening sound and reflecting/scattering sound.

A good thing about slatts is that when you use enough broadband absorption behind the slatts, the surface will be absorptive at lower frequensies , this will help against low frequensy combfiltering from the backwall (lbir, Ethan has an article about it on his site).

Last edited by hsal; 14th September 2011 at 11:01 PM.. Reason: some minor changes
Old 14th September 2011
  #21
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Boggy, adding on to my post above... the link you provided has a binary sequence that you developed. I might been completely wrong about this but...in making a slat/slot diffusor... this binary sequence tells you the random order to place slats. In other words, could I say that each binary position = 1 inch?
Binary "1" means "slat"
Binary "0" means "no slat"
Quote:
Originally Posted by soundoff View Post
In other words, from left to right on a slat/slot diffusor, according to the binary sequence, the first 6 inches (positions 0-5) would have slats of wood... followed by a 1 inch slot (position 6)... followed by a 1 inch slat (position 7) and so on???
Yes. If you find this sequence is too short for your needs use coin flipping and build your own (DIY) random binary sequence heh
Quote:
Originally Posted by soundoff View Post
If the above is correct... would the slats in positions 0-5 be touching? Do you leave a slight gap (say 1/8th of an inch or so) between them???
Yes, I usually include a slight gap
Old 15th September 2011
  #22
Gear Head
 

Okay... Perhaps this slat diffusor would be better suited to my needs. Seeing as though my seating is reasonably close to the back wall - 4 feet away - perhaps I should consider something that will provide both some absorption and some diffusion.

In terms of the width and thickness of the slats... Are there general guidelines for this?

I'm assuming the slats are installed against the insulation panel beneath them (no gap)?
Old 15th September 2011
  #23
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
............

In terms of the width and thickness of the slats... Are there general guidelines for this?
Thickness can be 1-2cm, width of slats define maximum working frequency (half of wavelength of max. working frequency is equal of slat width)... usually can be anything from 2-5cm
Quote:
Originally Posted by soundoff View Post
I'm assuming the slats are installed against the insulation panel beneath them (no gap)?
Yes, this is a way to keep your low frequency absorption virtually untouched (and a bit improved), and to bring back some liveliness in your room.

Binary diffusers make a balance between fully absorptive and fully reflective (and possibly resonant) surface in room.
Old 15th September 2011
  #24
Gear Head
 

Cool.

Is there a minimum and maximum range of frequencies that I should be looking to affect with the slats?

Also... In terms of the binary sequence. What would happen if I mixed the binary sequence with the 534 model I read about in another thread. Where as, I would use the binary sequence to tell me where to put slats and slots. And I would use the 534 model to guide the width if the slat or slot. For example... The binary might dictate 111010. And the other model might dictate 534453.

So, the first part of the diffusor would have a slat with the width designated for 5, followed by a slat with a width designated for 3... And so on?

Thoughts?
Old 15th September 2011
  #25
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John White's Avatar
 

Quote:
Originally Posted by soundoff View Post
What would happen if I mixed the binary sequence with the 534 model...
Or for that matter, how does the MLS and 345 compare with each other in terms of diffusion/absorbtion?

It would seem they would both have 50% solid surface area. My initial thought is the MLS would absorb to a higher frequency since most of the slats are potentially narrower. Interested to hear how this may affect the range of diffusion.
Old 15th September 2011
  #26
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Cool.

Is there a minimum and maximum range of frequencies that I should be looking to affect with the slats?
There is maximum frequency (half of wavelength = width of slats)... lowest frequency isn't clear and may be defined with whole width of diffuser.
EDIT: Lowest frequency is more limited by Schroeder frequency, from some frequency and below, you can't make more diffusion, even if you try wery hard.
But binary diffusion is very soft, not needed to have great expectation.

Quote:
Originally Posted by soundoff View Post
Also... In terms of the binary sequence. What would happen if I mixed the binary sequence with the 534 model I read about in another thread. Where as, I would use the binary sequence to tell me where to put slats and slots. And I would use the 534 model to guide the width if the slat or slot. For example... The binary might dictate 111010. And the other model might dictate 534453.
If you like to play, you can mix N13 QRD widths with MLS positions, and I'm pretty sure that N13 (even N7) QRD sequence works better than 534 heh
Quote:
Originally Posted by soundoff View Post
So, the first part of the diffusor would have a slat with the width designated for 5, followed by a slat with a width designated for 3... And so on?

Thoughts?
Too much simple!!!
Old 15th September 2011
  #27
Gear Head
 

Okay... I'm going to give this a shot. It will be rather basic. But, basic is better than nothing!

Because of the location of the window in the back of my room, it will be impossible to really mount this panel on the rear wall. Do you see any problem with me supporting it in front of the rear will (as close to the wall as possible) with legs and at the top with chains or some kind of anchor to keep it from falling?

Essentially it will be free standing in front of the rear wall.
Old 15th September 2011
  #28
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boggy's Avatar
Quote:
Originally Posted by soundoff View Post
Okay... I'm going to give this a shot. It will be rather basic. But, basic is better than nothing!

Because of the location of the window in the back of my room, it will be impossible to really mount this panel on the rear wall. Do you see any problem with me supporting it in front of the rear will (as close to the wall as possible) with legs and at the top with chains or some kind of anchor to keep it from falling?

Essentially it will be free standing in front of the rear wall.
I'm not sure that I understand you best, someone may answer you more precise. I only need to tell you that binary diffuser better works when it is in front of wideband and porous absorber, in this, amplitude grating mode, it will works much better than in phase grating mode when we have non porous and non absorbing surface behind slats (window in your case, if I understand good)
Old 15th September 2011
  #29
Gear Head
 

Quote:
Originally Posted by boggy View Post
But binary diffusion is very soft, not needed to have great expectation.
I guess this might be a great benefit for me. Seeing as though my seating position is close to the back wall (within 4 feet)... and the general advice I've read is that a more powerful diffusor is not necessarily good for seating in close proximity to the diffusor.

So, rather than deadening the whole back wall... I will be adding in some deadening and some diffusion.

I kind of feel like this is a blind stab... but it seems like there is enough agreement here to go ahead and give it a try!
Old 15th September 2011
  #30
Gear Head
 

Quote:
Originally Posted by boggy View Post
I'm not sure that I understand you best, someone may answer you more precise. I only need to tell you that binary diffuser better works when it is in front of wideband and porous absorber, in this, amplitude grating mode, it will works much better than in phase grating mode when we have non porous and non absorbing surface behind slats (window in your case, if I understand good)
Right. My fault for net describing properly...

The binary diffuser I'm going to build will be housed within a 6 ft wide by 5 ft tall frame. The slats will run vertically... and the entire surface behind the slats will be either 2" thick 705 acoustic panels OR 4" 705 acoustic panels.

This entire unit will basically be free standing right against the center of my back wall... the back wall has 2 large windows that will impede my ability to mount the diffuser directly to the wall, hence the reason it will need to be free standing.

Does that make better sense?
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