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post #1 of 13 Old 07-30-2013, 10:09 AM - Thread Starter
 
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Has anyone built these? http://www.pmerecords.com/Diffusor.cfm

any good/bad reviews on them? Are there any other good DIY diffusor designs to consider?
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post #2 of 13 Old 07-30-2013, 10:24 AM
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Those diffusers are probably fine, but most rooms do best with a 1D QRD diffuser on the rear wall. This site has plans and software and extensive technical advice:

Diffuser Calculator

These videos demonstrate the benefits of diffusion:

All About Diffusion
Hearing is Believing

--Ethan

RealTraps - The acoustic treatment experts

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post #3 of 13 Old 07-30-2013, 10:38 AM - Thread Starter
 
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Originally Posted by Ethan Winer View Post

Those diffusers are probably fine, but most rooms do best with a 1D QRD diffuser on the rear wall. This site has plans and software and extensive technical advice:

Diffuser Calculator

These videos demonstrate the benefits of diffusion:

All About Diffusion
Hearing is Believing

--Ethan

Thanks.

After reading for a while I think I will still go with a 2D QRD diffusor, as it is so much easier to build. When I buy the 2x2's from home depot they will cut them all there with their radial saw so it will be relatively easy to build these, basically just glue onto a piece of plywood.

Can you explain in the most general way possible the difference between 1D and 2D other than the fact 1D disperses left and right and 2D disperses left, right, up and down. Why don't you want a panel on the rear wall to disperse up and down?
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post #4 of 13 Old 07-30-2013, 01:50 PM
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I doubt Home Depot will cut all of those pieces for you. They'll probably give you a strange look when you tell them how many cuts they'd need to do. You may need to rent a miter saw for the day.

Ethan Winer says the benefit of 1D diffusers is you don't lose the acoustic energy like you would with a 2D diffuser because in a 2D diffuser the sound travels up and down as well. I built 2D diffusers though because, as you said, they are easier to build.

Ethan Winer's site says diffusers are only icing on the cake and are not required unless you have the funds. Yet in this video he posted, I hear a significant improvement in audio clarity with his QRD diffusers compared to an absorption panel or a bookcase. I'm not sure why he downplays diffusers?
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post #5 of 13 Old 07-30-2013, 01:56 PM - Thread Starter
 
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Originally Posted by brandon_k_w View Post

I doubt Home Depot will cut all of those pieces for you. They'll probably give you a strange look when you tell them how many cuts they'd need to do. You may need to rent a miter saw for the day.

Ethan Winer's site says diffusers are only icing on the cake and are not required unless you have the funds. Yet in this video he posted, I hear a significant improvement in audio clarity with his QRD diffusers compared to an absorption panel or a bookcase. I'm not sure why he downplays diffusers?

The homedepot by me will cut anything as many times as you like. I always get tons of stuff randomly cut. It actually doesn't take that long to cut these 2x2s for diffuser panels, because they can put like twelve 2x2's through their radial saw at a time so you can get 12 pieces cut per cut.
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post #6 of 13 Old 07-30-2013, 04:55 PM
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Why not make your Skyline out of styrofoam?
Half the work, and instead of having to "Bolt" it on
the wall or ceiling you can use simple scews
due to the weight differences.

I've built big 1D QRD out of styrofoam with great success.
Placed it on the front wall, I run Dipole speakers.
Next will be some skylines for the rear of the room.

Should be able to see it in my avatar.
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post #7 of 13 Old 07-30-2013, 05:49 PM - Thread Starter
 
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Quote:
Originally Posted by Perry R View Post

Why not make your Skyline out of styrofoam?
Half the work, and instead of having to "Bolt" it on
the wall or ceiling you can use simple scews
due to the weight differences.

I've built big 1D QRD out of styrofoam with great success.
Placed it on the front wall, I run Dipole speakers.
Next will be some skylines for the rear of the room.

Should be able to see it in my avatar.

didn't think styrofoam worked well for diffusers. do you have a link to plans for them or anything?
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post #8 of 13 Old 07-30-2013, 06:50 PM
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I was under the impression Styrofoam had problems diffusing all the targeted frequencies. Wood is much more reflective. Make your diffusers with wood like mine:

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post #9 of 13 Old 07-31-2013, 04:25 AM
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Quote:
Originally Posted by JWagstaff View Post

Quote:
Originally Posted by Perry R View Post

Why not make your Skyline out of styrofoam?
Half the work, and instead of having to "Bolt" it on
the wall or ceiling you can use simple scews
due to the weight differences.

I've built big 1D QRD out of styrofoam with great success.
Placed it on the front wall, I run Dipole speakers.
Next will be some skylines for the rear of the room.

Should be able to see it in my avatar.

didn't think styrofoam worked well for diffusers. do you have a link to plans for them or anything?

(1) Not all styrofoam is the same. Some is denser and less acoustically transparent at low frequencies. And there is an important point, most diffusers like these are small enough that they can't do much at low frequencies because of their size, regardless of what they are made up out of.

(2) If you have any doubts, coat your diffuser with polyester resin, thin latex masonry coating, or some other coating that seals it up but doesn't eat up the plastic.
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post #10 of 13 Old 07-31-2013, 04:28 AM
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Quote:
Originally Posted by brandon_k_w View Post

I doubt Home Depot will cut all of those pieces for you. They'll probably give you a strange look when you tell them how many cuts they'd need to do. You may need to rent a miter saw for the day.

Ethan Winer says the benefit of 1D diffusers is you don't lose the acoustic energy like you would with a 2D diffuser because in a 2D diffuser the sound travels up and down as well. I built 2D diffusers though because, as you said, they are easier to build.

Ethan Winer's site says diffusers are only icing on the cake and are not required unless you have the funds. Yet in this video he posted, I hear a significant improvement in audio clarity with his QRD diffusers compared to an absorption panel or a bookcase. I'm not sure why he downplays diffusers?

If memory serves, Ethan's demo adds diffusers to a room that was already well-treated with absorbers. Absorbers often help the effects of diffusers be more audible.
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post #11 of 13 Old 07-31-2013, 02:45 PM
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Originally Posted by arnyk View Post

If memory serves, Ethan's demo adds diffusers to a room that was already well-treated with absorbers. Absorbers often help the effects of diffusers be more audible.

Yes, though I linked two different videos above.

Brandon, diffusers do give a more "open" sound than absorbers, so it's not that I downplay diffusers as much as I respect that not everyone has a large budget. The treatment in the Hearing is Believing video costs about $14,000 as I recall. Versus 1/2 or even 1/3 that for a serious amount of absorption only. But yes, when someone wants The Best (tm) and has the budget to match, diffusion (plus lots of bass trapping) is the way to go.

--Ethan

RealTraps - The acoustic treatment experts

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post #12 of 13 Old 08-01-2013, 07:15 AM
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Quote:
Originally Posted by JWagstaff View Post

Has anyone built these? http://www.pmerecords.com/Diffusor.cfm

any good/bad reviews on them? Are there any other good DIY diffusor designs to consider?

that is not a QRD, so i am not sure why it is labeled so. it's actually an old BBC design composed of many smaller PRDs into an array; hence why the wells are 12x12 and thus do not correspond to a single primitive root diffuser (12x12 are not co-primes). a PRD based on P157 would yield 13x12 wells (13x12 = (157-1)), for example.

diffusers (phase gratings, in this case), break-up sparse reflections into many reflections spatially and temporally dispersed (grating lobes). a 2D diffuser (your example), disperses energy in the vertical and horizontal planes, while a 1dimensional phase grating will disperse in the opposing plane of the wells (eg, a 1dimensional diffuser oriented such that the wells are vertical yields spatial dispersion in the horizontal plane).

you first need to understand the requirements of your room and how you want to introduce indirect specular returns to the listening position. for a 2ch environment (if emulating the LEDE response), you would utilize 1dimensional phase gratings on the rear wall/side walls with the wells oriented vertically to provide a lateral-arriving diffuse-field for passive envelopment. a surround sound environment has active surround sources, so a 2D may be more appropriate since the passive lateral returns are not needed. a 2D will also have an inherently higher absorption coefficient due to the increase in number of wells (1/4wave reson and edge diffraction losses), on top of the additional losses due to redirecting energy in both planes. regardless, care needs to be taken with respect to construction to seal any/all gaps to eliminate excessive losses.

you will want to be in the far-field of the diffuse returns, and as such it is best guideline to have listening position be at least 3x wavelength of the design freq away from the diffuser. eg, if your listening setup is ~ 7ft from the diffuser, then you would utilize a design freq of 500hz (corresponding to 2.26ft wavelength; 3*2.26 = ~6.8ft). this requirement can pose issues in smaller rooms with many seats and as such you will commonly see Binary Amplitude Diffusers (BAD) utilized, but these devices will only offer spatial dispersion (no temporal dispersion).

instead of blindly following a diffuser template, it is best to utilize a QR or PR calculator in order to design the diffuser based on your criteria: minimum seating distance to diffuser (=design frequency), sq area / array size you need to cover, complexity of construction, prime#, etc.

a 2D primitive root calculator can be found here: http://www.oliverprime.com/prd/?show=gallery
a 1D/2D quadratic residue calc can be found here: http://www.subwoofer-builder.com/qrdude.htm

QRDude is a wonderfully written app and you should take some time to read through the technical guide of which will detail the physical aspects of the behavior: http://www.subwoofer-builder.com/qrd.htm
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post #13 of 13 Old 09-07-2013, 10:23 AM
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Originally Posted by localhost127 View Post

that is not a QRD, so i am not sure why it is labeled so. it's actually an old BBC design composed of many smaller PRDs into an array; hence why the wells are 12x12 and thus do not correspond to a single primitive root diffuser (12x12 are not co-primes). a PRD based on P157 would yield 13x12 wells (13x12 = (157-1)), for example.

diffusers (phase gratings, in this case), break-up sparse reflections into many reflections spatially and temporally dispersed (grating lobes). a 2D diffuser (your example), disperses energy in the vertical and horizontal planes, while a 1dimensional phase grating will disperse in the opposing plane of the wells (eg, a 1dimensional diffuser oriented such that the wells are vertical yields spatial dispersion in the horizontal plane).

you first need to understand the requirements of your room and how you want to introduce indirect specular returns to the listening position. for a 2ch environment (if emulating the LEDE response), you would utilize 1dimensional phase gratings on the rear wall/side walls with the wells oriented vertically to provide a lateral-arriving diffuse-field for passive envelopment. a surround sound environment has active surround sources, so a 2D may be more appropriate since the passive lateral returns are not needed. a 2D will also have an inherently higher absorption coefficient due to the increase in number of wells (1/4wave reson and edge diffraction losses), on top of the additional losses due to redirecting energy in both planes. regardless, care needs to be taken with respect to construction to seal any/all gaps to eliminate excessive losses.

you will want to be in the far-field of the diffuse returns, and as such it is best guideline to have listening position be at least 3x wavelength of the design freq away from the diffuser. eg, if your listening setup is ~ 7ft from the diffuser, then you would utilize a design freq of 500hz (corresponding to 2.26ft wavelength; 3*2.26 = ~6.8ft). this requirement can pose issues in smaller rooms with many seats and as such you will commonly see Binary Amplitude Diffusers (BAD) utilized, but these devices will only offer spatial dispersion (no temporal dispersion).

instead of blindly following a diffuser template, it is best to utilize a QR or PR calculator in order to design the diffuser based on your criteria: minimum seating distance to diffuser (=design frequency), sq area / array size you need to cover, complexity of construction, prime#, etc.

a 2D primitive root calculator can be found here: http://www.oliverprime.com/prd/?show=gallery
a 1D/2D quadratic residue calc can be found here: http://www.subwoofer-builder.com/qrdude.htm

QRDude is a wonderfully written app and you should take some time to read through the technical guide of which will detail the physical aspects of the behavior: http://www.subwoofer-builder.com/qrd.htm


So, obviously your knowledgeable, localhost127 - so what does your setup look like?
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