QRDude - Diffuser Calculator - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 18 Old 06-15-10, 02:07 AM
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Re: QRDude - Diffuser Calculator

Hello Collo

The Diffuser Calculator is a really nice tool, which I came across a while back. In it you specify a minimum seating distance. What determines this? As I have a small room distances are not enough to have a diffuser going to lower frequencies. What happens if the minimum seating distance is not adhered to?

rgds

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post #12 of 18 Old 06-15-10, 02:48 AM Thread Starter
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Re: QRDude - Diffuser Calculator

The minimum distance is based on three times the lowest wavelength diffused. This is an industry convention, but Ethan Weiner reckons you can be closer and still get benefits. He has some videos on his Realtraps site that let you hear the difference

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post #13 of 18 Old 06-15-10, 04:31 AM
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Re: QRDude - Diffuser Calculator

I don't understand why it should be 3 x the wavelength of the lowest frequency, why not 1 x? Do you have any practical experience with this?
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post #14 of 18 Old 06-15-10, 06:51 PM Thread Starter
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Re: QRDude - Diffuser Calculator

The response from the panel is made up of cancellations and re-inforcements due to the energy exiting each of the wells at a different phase. My understanding is that it takes a few cycles for this to settle into a stable wavefront.
See my optional reading panel on huygens principle of diffusion in the Technical overview of QRDs for the drawing.

I had a quick look for the 3 wavelength rule, but couldn't find it. Google is your friend there.
As for experience, I haven't done any installations, thus the referral to industry experts like Ethan, or the guys from GIK.

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post #15 of 18 Old 07-04-10, 02:11 PM
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Re: QRDude - Diffuser Calculator

Hi Collo,

Great program!

In Cox and D'Antonio they state that the QRD design assumes a far field (9.9 But ...) and that this is defined as the region where the min and max path length to the diffuser/receiver is less than half a wave length (8.4.1 Near and far field). Using this definition the critical wavelengths are associated with the high frequencies and not the low ones. See equation 8.35: distance > (diffuser_width/2)^2/wave_length.

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post #16 of 18 Old 07-04-10, 06:31 PM Thread Starter
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Re: QRDude - Diffuser Calculator

Thanks for those comments Marcus. you have inspired me to look a bit further....

Your information does indeed define what constitutes the "far field", however most listening is within the near field.

Here is the Google books display of the section in the Cox and D'Antonio book that gives the 3 wavelength rule. (Section 2.2.1)

Rather than give a proof, they state that "Precedence has shown"... suggesting that the rule was derived from their extensive testing experience.

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Last edited by collo; 07-05-10 at 08:36 PM.
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post #17 of 18 Old 07-05-10, 11:58 AM
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Re: QRDude - Diffuser Calculator

Hi Collo,

Quote:
collo wrote: View Post
Your information does indeed define what constitutes the "far field", however most listening is within the near field.
That does appear to be one one of the limitations of the design. Have you put your mind around Schroeder's proposed solution to the near / far field problem? If one was to 'modulate the the well depths to follow a parabolic concave mirror' as suggested by Cox and D'Antonio where would one but the focal point? At the listening position? at 3 time the wavelength? The opposite wall?

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post #18 of 18 Old 07-05-10, 08:46 PM Thread Starter
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Re: QRDude - Diffuser Calculator

Such an approach would be impractical for most rooms.

Also, the situation changes with the angle of incidence of the incoming signal, as pointed out at the end of section 8.4.1

I couldn't see the point of trying to focus the sound to one region, when it's diffusion we are after...

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