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Author Topic: D.I.Y. Diffusers  (Read 44499 times)

Bill B

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Re: D.I.Y. Diffusers
« Reply #30 on: October 04, 2005, 01:19:30 pm »

jimmyjazz wrote on Tue, 04 October 2005 10:24

What's the frequency range of your diffusors?  How deep into the bass region do they extend?


I haven't done any serious testing yet (still building my new room) but I thought I read in the BBC R&D report that they worked down to around 800Hz. I don't know how much lower diffusion would be useful, but at some point I'm sure there's a diminishing return.
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jimmyjazz

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Re: D.I.Y. Diffusers
« Reply #31 on: October 04, 2005, 01:26:54 pm »

http://www.bbc.co.uk/rd/pubs/reports/1990-15.pdf

is referenced in badbear's paper.  I haven't dug into it yet, but it appears to describe the theory of diffusers in some detail.
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bounce

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Re: D.I.Y. Diffusers
« Reply #32 on: October 04, 2005, 04:19:25 pm »

Hi. I layed out the measurement grid from the BBC doc if anyone wants to build these "block" style diffusors. Here's the grid (height ratio of blocks):

0 3 4 1 2 3 3 1 4 2 3 3
3 0 1 4 2 1 1 3 3 2 1 1
3 1 1 3 1 3 2 2 1 0 2 2
2 2 2 2 0 4 3 2 3 2 1 1
3 3 1 1 3 1 1 3 4 3 1 3
2 3 2 1 2 0 3 2 4 2 1 0
2 3 2 1 3 1 2 2 3 1 3 4
2 0 2 4 4 0 1 2 1 4 2 2
3 4 1 0 1 3 3 1 0 2 3 3
1 3 3 1 2 4 1 2 0 1 3 1
2 1 2 3 1 3 3 2 4 2 3 4
2 4 2 3 3 1 1 2 0 3 1 0

And here's a list of how many of each length block you will need when precutting the wood:

Count of number:

number   Total pieces of this length (height actually) of wood

0   13 (no cuts here if you're going flush with the surface)
1   38
2   38
3   40
4   15

Grand Total   144 pieces (131 if 0's aren't used)

I assume these will work with 1x1 or 2x2 inch squares (cut longer depending on the graph number- ie. graph designating number 3 would mean use a 1x3 inch block or 2x6 if using 2x2's)...I'll have to break out the saw!

mckay
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McKay Garner
Bounce Inventive Audio
Los Angeles

Bill B

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Re: D.I.Y. Diffusers
« Reply #33 on: October 04, 2005, 05:24:20 pm »

I considered making some from 2x2's as well. They would wiegh more,  but diffuse more surface area per unit.
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Bill B

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Re: D.I.Y. Diffusers
« Reply #35 on: October 06, 2005, 08:58:27 pm »

Ivo, those look great. Are they from a kit?
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Ivo

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Re: D.I.Y. Diffusers
« Reply #36 on: October 07, 2005, 02:21:54 am »

There are DIY (or rather LCDI = let a carpenter do it Smile ) exactly according to Schroder algorithms (in two sizes). 140x70 and 90x45. They are more or less the same as RPG diffusers at a fraction of cost ...
I already tried to play violin there, sounds very nice, full and spacy ...
You can also notice huge "superchunk" corner absorbers (DIY )

No I would like to add some cylimndrical polydiffusers on the side walls, but rather simple wooden ones
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Ivo

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Bill B

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Re: D.I.Y. Diffusers
« Reply #37 on: October 07, 2005, 09:54:50 am »

Any chance you could share the plans with us?
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Ivo

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Re: D.I.Y. Diffusers
« Reply #38 on: October 07, 2005, 12:15:46 pm »

There is no secret in it. Just two selected Schroder algrorithms:

1)
11 wells
Well width 6 cm
Well depths:
2,8,18,10,6, 6, 10, 18, 8, 2, 0  cm
about 1 cm ribs in between each well

Size 70x140cm

2) 7 wells
Well width 5,7 cm
Well depths:
3,12,6,6,12,3, 0 cm

Size 45x90 cm

Now I am looking for some tips (and photos) for simple cylindrical polydiffusers
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Ivo

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stuntbutt

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Re: D.I.Y. Diffusers
« Reply #40 on: October 08, 2005, 08:08:27 pm »

Does anyone know if the well dividers are necessary in a quadratic residue diffuser?  I've seen big ones without the dividers.  We are talking well widths of over a foot and depths out to 2 feet.  All the more normal scaled ones I've seen have had the well dividers.  I'm wondering because I have an idea for simple construction that does not include well dividers.
-------------------------------------------------
John Katsafanas
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Ivo

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Re: D.I.Y. Diffusers
« Reply #41 on: October 09, 2005, 02:40:01 am »

I have read that the well dividers are quite necessary to avoid phase problems when the sound addresses the diffuser from the side.
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Ivo

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stuntbutt

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Re: D.I.Y. Diffusers
« Reply #42 on: October 09, 2005, 02:57:13 am »

Thanks Ivo.  Congratulations on your room.
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Ivo

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Re: D.I.Y. Diffusers
« Reply #43 on: October 09, 2005, 06:33:26 am »

Now I plan to make few big cylindrical polydiffusors on the side walls (just simple slightly curved plywood on the frame). I wonder - what acoustic difference does it make to add some rockwool layer on the bent plywood from inside or to keep it simply plain? Or to put rockwool inside the frame on the wall ? Just to bend the plain plywood would be the easiest of course ...
The main purpose would be to erase the flutter between the side walls without too much "deadenig" the room.
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Ivo

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matucha

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Re: D.I.Y. Diffusers
« Reply #44 on: October 09, 2005, 07:37:04 am »

Wow, Ivo is becoming DIY acoustic "specialist", congrats Wink.

There is a link at the johnlsayers.com forum to xls calculator, that calculates room modes etc... and it also calculates shroeder diffusor parameters. It gives you idea what freq. range will be diffused so you can "design" it to fit your needs.
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