DIY Diffusor plans, pick it apart guys :)

[davecfraser]

My plan is to build a few N47 Diffusor 1/8 inch fins made of HDF and 3/4 inch well width that is 45" high and approximately 45" wide. The depth of this unit will be 7 inches.

I'm going to install them on the sidewalls of my listening position (the upper wall between "1" and "2"

http://www.davidcavanfraser.com/davi.../dcfstudio.gif

Some Questions:


QRDude says it will diffuse down to 836 HZ and scatter at half of that (428 HZ). However, the GIK Q7D diffusor is only 6" deep and it says it can scatter down to 350hz, how is this achieved?

Also boggy seems to think a 0.75 inch well width is okay, but QRDude says I'm going to experience Viscous losses. Is it a big deal?

Another question was should we fill the cavity behind the well face of the diffusor with Roxul for bass trapping? How much benefit will this actually provide?

If anyone sees any flaws in my design, let me know!

Thanks a bunch!

[Jens Eklund]

Originally Posted by davecfraser

However, the GIK Q7D diffusor is only 6" deep and it says it can scatter down to 350hz, how is this achieved?

That sounds a tad optimistic. Have you found any measurements or BEM predictions confirming that? Perhaps if measuring (or simulating) only a single panel you might end up with such high numbers but a single panel will always produce impressive results not related to real world applications.

Also, there’s the definition of “effective” scattering/diffusion … I once made some high resolution (1/24 oct) simulations of a QRD N7 (3 or 6 periods, total panel width 3,6 meters) but the panel depth (total and effective) was 220/190 mm (8,7”/7,5”):

[Jens Eklund]

Originally Posted by davecfraser

Another question was should we fill the cavity behind the well face of the diffusor with Roxul for bass trapping? How much benefit will this actually provide?

my new diffusor, thanks to gs

[Jens Eklund]

Originally Posted by davecfraser

Also boggy seems to think a 0.75 inch well width is okay, but QRDude says I'm going to experience Viscous losses. Is it a big deal?

I think that the losses would be considerable even if 1,5-2" well width. This is one reason I like stepped diffusers.

[davecfraser]

What are these "losses" (viscous?)

Could you explain what I'm sacrificing here, I understand QRD diffusors are always a compromise. But what am I compromising?

[Jens Eklund]

Originally Posted by davecfraser

What are these "losses" (viscous?)

Could you explain what I'm sacrificing here, I understand QRD diffusors are always a compromise. But what am I compromising?

Loss of energy: absorption.

A good diffuser should not absorb (at least not within its operational range but naturally all do more or less but less is better), it is supposed to redistribute the energy evenly in the plane(s) of operation.

[davecfraser]

What will the frequency range of absorption be? Approximately the same as the frequency range of our diffusor (967hz to 9Khz)ish?

[localhost127]

Originally Posted by davecfraser

What are these "losses" (viscous?)

Could you explain what I'm sacrificing here, I understand QRD diffusors are always a compromise. But what am I compromising?

via: Amazon.com: Acoustic Absorbers and Diffusers: Theory, Design and Application (9780415471749): Trevor J. Cox, Peter D'Antonio: Books

[Jens Eklund]

Originally Posted by davecfraser

What will the frequency range of absorption be? Approximately the same as the frequency range of our diffusor (967hz to 9Khz)ish?

If you have access to the excellent book "Acoustic Absorbers and diffusers (SE)", look no further than page 321. If not; the graph shows significant absorption (for this example) above about 400 Hz.

EDIT: ... I´m late to the party ...

[localhost127]

Originally Posted by Jens Eklund

If you have access to the excellent book "Acoustic Absorbers and diffusers (SE)", look no further than page 321. If not; the graph shows significant absorption (for this example) above about 400 Hz.