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QRD with only 1cm well width? Channel Strips
Old 13th September 2011
  #1
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QRD with only 1cm well width?

Just a simple question, i hope there is a simple answer...
Since we have tons of a material called HSP (Hartschaumplatte in German, translates "Hard Foam Plate").
It´s very light and is 1cm strong.
I would like to build some qrds for my ceiling.
So i was thinking of using those boards "sideways" for easy construction.
So the wells would be 1cm, fins 1mm aluminium.
Depth maybe something around 8 or 10 cm.
I´ll run up my pc system for qrdude, see what it tells me.
But anyway, will a few of these 50*50cm panels (say a 47 step sequence) do any good on the ceiling about 250cm high?
Old 13th September 2011
  #2
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Quote:
Originally Posted by jrp View Post
Just a simple question, i hope there is a simple answer...
Since we have tons of a material called HSP (Hartschaumplatte in German, translates "Hard Foam Plate").
It´s very light and is 1cm strong.
I would like to build some qrds for my ceiling.
So i was thinking of using those boards "sideways" for easy construction.
So the wells would be 1cm, fins 1mm aluminium.
Depth maybe something around 8 or 10 cm.
I´ll run up my pc system for qrdude, see what it tells me.
narow slats has a bit higher absorption but I think that this diffusers can be worthwile if you have a lot of this boards.
Also you can possibly glue two boards together then use 20mm wor well width.
Quote:
Originally Posted by jrp View Post
But anyway, will a few of these 50*50cm panels (say a 47 step sequence) do any good on the ceiling about 250cm high?
Yes, it will do some diffusion, but if you don't have dampened room modes already in your room, you can't easily notice effects of diffusion.
Old 13th September 2011
  #3
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What exactly are serious viscous losses? QRDude always gives that warning for well width below 25mm.

For a qrd with 47 wells with 1cm width and 9cm deep QRDude tells me:

Scatter 851 Hz Diffuse 1703 Hz HF cutoff 17200 Hz

Period width 517 mm

Minimum distance to seating position .6m (3 times wavelength of lowest diffusion frequency)

Good result: Period width of 517mm is is not less than the design wavelength of 202 mm

Poor result: The well width less than the minimum 25mm to avoid viscous losses - Serious viscous losses may be encountered

Good result: Plate frequency of 80041 hz is higher than HF cutoff of 17200 hz, so it has no effect

Good result: The HF cutoff frequency of 17200 hz is 10 times the design frequency of 1703 hz

True diffusion frequencies: 1703 3406 5109 6812 8515 10218 11921 13624 15327 17030 hz
Old 13th September 2011
  #4
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ah, thanks. Of course, basstrapping is first and most important.
I already did this to my controll room, now i am starting to treat our live room.

Going for 20mm QRDude gives the same warning, the data is now this:
Scatter 748 Hz Diffuse 1496 Hz HF cutoff 8600 Hz

Period width 483 mm

Minimum distance to seating position .68m (3 times wavelength of lowest diffusion frequency)

Good result: Period width of 483mm is is not less than the design wavelength of 230 mm

Poor result: The well width less than the minimum 25mm to avoid viscous losses - Serious viscous losses may be encountered

Good result: Plate frequency of 34408 hz is higher than HF cutoff of 8600 hz, so it has no effect

Good result: The HF cutoff frequency of 8600 hz is 5.7 times the design frequency of 1496 hz

True diffusion frequencies: 1496 2992 4488 5984 7480 hz
Old 13th September 2011
  #5
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i'll probably get shot down here but does viscous loss occur when one well absorbs energy from the adjacent well??? not sure....
Old 13th September 2011
  #6
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Quote:
Originally Posted by jrp View Post
ah, thanks. Of course, basstrapping is first and most important.
I already did this to my controll room, now i am starting to treat our live room.

Going for 20mm QRDude gives the same warning, the data is now this:
Scatter 748 Hz Diffuse 1496 Hz HF cutoff 8600 Hz

Period width 483 mm

Minimum distance to seating position .68m (3 times wavelength of lowest diffusion frequency)

Good result: Period width of 483mm is is not less than the design wavelength of 230 mm

Poor result: The well width less than the minimum 25mm to avoid viscous losses - Serious viscous losses may be encountered

Good result: Plate frequency of 34408 hz is higher than HF cutoff of 8600 hz, so it has no effect

Good result: The HF cutoff frequency of 8600 hz is 5.7 times the design frequency of 1496 hz

True diffusion frequencies: 1496 2992 4488 5984 7480 hz
I successfully design many diffusers with wells width 18-24mm. Some viscous losses can't destroy existing diffusion effect.
I never use 10mm for well width, so I can't recommend it. But 20mm is ok.
Old 13th September 2011
  #7
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maybe i will do both and mix them.
With the 1cm version i could even make it a little less deep so it affects the high end only, say 3-17khz.
I wonder what happens if i build it without fins. I know the fins are there for a reason (that i don´t know) but i could imagine that it would still do something and would be a very easy and cheap build...
I would probably make three individual units placed 1cm appart for my ceiling being the steps with 0 block hight.
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