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Author Topic: Diffusion front or back?  (Read 2757 times)

jfrigo

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Diffusion front or back?
« on: August 27, 2006, 12:03:35 am »

The traditional LEDE room has a soft (absorptive) front and a diffuse back. However, some newer rooms have diffusion (often 2D) up front, behind the speakers. This certainly makes bass trapping directly behind the listener easy to construct, but it does change things.

What do you feel the differences are between each approach? Are there pros and cons to each? Any reason 2D seems more popular up front while 1D is popular in back (not exclusively of course)?

Thanks again. Enjoying having you around.
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franman

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Re: Diffusion front or back?
« Reply #1 on: August 27, 2006, 04:18:46 pm »

okay now I will open a large can of worms..... (proceed carefully)

We generally use the modified LEDE approach called RFZ (Reflection Free Zone) that is intended to control and or steer all early reflections from the listening position... This calls for the rear wall diffusor installed with the guidelines already listed in several other posts... (time and distance).

I do make use of Abfussors in the front/side walls in a lot of our designs and these are often mistaken for diffusors. They are QRD based absorbers from RPG that really clean up imaging issues for us very well when placed at positions of first reflection. They look like a QRD, but are made from Homosote and Rigid Fiberglasss (absorptive materials). They provide extended LF absorption for their 4" depth by the nature of the phase grating affect....

We DO use front loaded diffusors in dedicated surround suites. I always thought that for a true 5.1 installation the surrounds should get "equal consideration" as far as the diffuse return. Placement is tricky as you don't want these diffusors to be "visible" to the direct or first reflected sound from the front speaker array... This is where we earn our money!!

But generally, for a stereo critical listening environment, we do not use front diffusors. We don't want diffuse return in that short time frame as it will cloud the imaging reproduction in the recording... (this is another large can of worms)...

I think I'll get Lars to post his paper he wrote on the implications and affect of early reflections in critical sound reproduction. It uses the TEF ETC displays to graphical demonstrate what happens with a lot of early reflections in a playback environment. Good stuff!!! Lars, if you read this, please consider posting that paper online here.....
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jetbase

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Re: Diffusion front or back?
« Reply #2 on: August 30, 2006, 09:32:01 pm »

franman wrote on Mon, 28 August 2006 06:18

I do make use of Abfussors in the front/side walls in a lot of our designs and these are often mistaken for diffusors. They are QRD based absorbers from RPG that really clean up imaging issues for us very well when placed at positions of first reflection. They look like a QRD, but are made from Homosote and Rigid Fiberglasss (absorptive materials). They provide extended LF absorption for their 4" depth by the nature of the phase grating affect....




is that anything like the "binary amplitude grating" mentioned here: http://www.audioholics.com/techtips/setup/acoustics/RPG-Room acoustics.html (about 2/3 down the page)?
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franman

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Re: Diffusion front or back?
« Reply #3 on: August 31, 2006, 11:34:20 pm »

The Binary Amplitude Diffusor (BAD) is a relatively new flat diffusor that RPG has come up with that combines an absorptive panel with a Number Sequence cover skrim made from a hard materials such as thin masonite or metal... we have used these with good success in smaller rooms as well, where  the rear wall is too close for a full on QRD or DFR style diffusor... Check photos from UMG Mastering on our site for some pretty slick metal BAD Curved panels...
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Francis Manzella - President, FM Design Ltd.
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jetbase

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Re: Diffusion front or back?
« Reply #4 on: September 01, 2006, 02:50:19 am »

so not the same phasing issues when in close proximity? i wonder if this would be good for small recording rooms too.
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sleep is not an option

jwhynot: "There's a difference between thinking or acting dogmatically and drawing from experience."


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franman

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Re: Diffusion front or back?
« Reply #5 on: September 02, 2006, 10:15:07 pm »

Both abfussors and BAD panels could be used advantageously in recording rooms at closet distances...
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Francis Manzella - President, FM Design Ltd.
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