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gavintheaudioengineer
gimme a little kick & snare
Joined: 16 Nov 2010
Posts: 78
Location: UK
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 Posted: Fri Feb 24, 2012 8:07 am Post subject: TO#83 BBC Diffusors |
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So I'm looking to build a few of these diffusors for myself, and this guide in the tape op mag is great!
Just one thing- the author states that the squares of ply should be 18 x 18, but I'm counting 24 x 24 on the diagram- am I missing something?
Does anyone have any idea which is the correct size and array to adhere to the BBC specs?
Any help appreciated!
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gavintheaudioengineer
gimme a little kick & snare
Joined: 16 Nov 2010
Posts: 78
Location: UK
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| Posted: Fri Feb 24, 2012 8:40 am Post subject: Re: TO#83 BBC Diffusors |
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and here http://www.pmerecords.com/Diffusor.cfm again, the guide says to cut the square to 18 x 18, but the amount of 2x2 blocks on each edge amounts to 24 x 24.
Which is right?
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DrummerMan
tinnitus
Joined: 05 Jun 2008
Posts: 1195
Location: Los Angeles
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| Posted: Fri Feb 24, 2012 10:30 am Post subject: Re: TO#83 BBC Diffusors |
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A 2x2 you buy at a typical lumber place in the states is, in fact, planed down to 1 1/2x1 1/2. This brings you to 18" total in the end.
I don't know how lumber is in the UK though.
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Geoff Mann
Composer - Los Angeles, CA |
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Rod Gervais
alignin' 24-trk
Joined: 05 Aug 2006
Posts: 52
Location: Central Village, CT
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| Posted: Sun Feb 26, 2012 9:59 am Post subject: Re: TO#83 BBC Diffusors |
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| DrummerMan wrote: | A 2x2 you buy at a typical lumber place in the states is, in fact, planed down to 1 1/2x1 1/2. This brings you to 18" total in the end.
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Correct - the advertised dimensions of lumber here in the States are nominal sizes related to the rough sawn conditions of the lumber at the saw mill.
So a 1x4 is actually close to 3/4" x 3 1/2" - while a 2x4 is about 1 1/2" x 3 1/2".
Note that I am (quite deliberately) using approximate dimensions here........ this because even the dressed numbers are not always that accurate when dealing with lumber from different lumberyards.
I have seen 2x_ (2, 4, 6, 8, 10, 12,) measure anywhere from 1 3/8" to 1 5/8" in thickness - with as much as a 1/2" variance in width. However, none of that really makes any difference in the long run.
Rod
Last edited by Rod Gervais on Mon Feb 27, 2012 10:36 am; edited 1 time in total |
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rhythm ranch
moves faders with mind
Joined: 07 May 2003
Posts: 2623
Location: Corrales, NM
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| Posted: Sun Feb 26, 2012 12:48 pm Post subject: Re: TO#83 BBC Diffusors |
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| Rod Gervais wrote: | So a 1x4 is actually close to 3/4" x 3 1/2" - while a 2x4 is about 1 1/2" x 3 1/2".
Rod |
Fixed
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Rod Gervais
alignin' 24-trk
Joined: 05 Aug 2006
Posts: 52
Location: Central Village, CT
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| Posted: Mon Feb 27, 2012 10:37 am Post subject: Re: TO#83 BBC Diffusors |
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| rhythm ranch wrote: | | Rod Gervais wrote: | So a 1x4 is actually close to 3/4" x 3 1/2" - while a 2x4 is about 1 1/2" x 3 1/2".
Rod |
Fixed |
Thanks - brain fart on my part........ 
Rod |
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gavintheaudioengineer
gimme a little kick & snare
Joined: 16 Nov 2010
Posts: 78
Location: UK
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| Posted: Thu Mar 01, 2012 9:06 am Post subject: Re: TO#83 BBC Diffusors |
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Thanks guys, that makes sense now.
So I'll stick with 18 x 18 and see how things go!
Exciting
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AlexHerd
gettin' sounds
Joined: 23 Sep 2003
Posts: 149
Location: Pittsburgh
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| Posted: Wed Mar 07, 2012 3:44 pm Post subject: Re: TO#83 BBC Diffusors |
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| I've built 8 of these and they are indeed 18x18 |
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nobody, really
gettin' sounds
Joined: 03 Aug 2010
Posts: 116
Location: where the sidewalk ends
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| Posted: Fri Mar 09, 2012 10:59 am Post subject: Re: TO#83 BBC Diffusors |
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| Does anyone know if you can use 4x4's in place of the 2x2's? Is it just the length differences that matter? I have a lot of 4x cutoffs... |
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floid
steve albini likes it
Joined: 03 Jan 2006
Posts: 380
Location: Starkville, MS
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| Posted: Fri Mar 09, 2012 11:27 am Post subject: Re: TO#83 BBC Diffusors |
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the other night i had one of those, you know, "inspired moments" when it seemed like it would be pure genius to build a pile of these in appropriate depth ratios to cover an entire wall or ceiling in the same pattern - kind of like a single order fractal.
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vxboogie
pushin' record
Joined: 06 Aug 2008
Posts: 262
Location: OH
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| Posted: Fri Mar 09, 2012 11:55 am Post subject: Re: TO#83 BBC Diffusors |
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Has anyone ever made these out something other than wood, like closed cell foam or something? I'm not sure how that would affect the reflection and hense the diffusion, though. It just seems like there should be an easier, lighter way than wood.
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Mark - Listen, turn knob, repeat as necessary... |
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JWL
carpal tunnel
Joined: 02 Apr 2006
Posts: 1537
Location: Portland, Maine
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| Posted: Fri Mar 09, 2012 2:42 pm Post subject: Re: TO#83 BBC Diffusors |
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| nobody, really wrote: | | Does anyone know if you can use 4x4's in place of the 2x2's? Is it just the length differences that matter? I have a lot of 4x cutoffs... |
Great question. As far as I know, making each "block" larger will lower the effective top-end range of the diffusor; put another way, it won't diffuse to as high a frequency. The depth of each well determines the low frequency cutoff.
If you want, you can plug in the numbers at QRDude and see for yourself: http://www.subwoofer-builder.com/qrdude.htm
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JWL
carpal tunnel
Joined: 02 Apr 2006
Posts: 1537
Location: Portland, Maine
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| Posted: Fri Mar 09, 2012 2:44 pm Post subject: Re: TO#83 BBC Diffusors |
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| vxboogie wrote: | | Has anyone ever made these out something other than wood, like closed cell foam or something? I'm not sure how that would affect the reflection and hense the diffusion, though. It just seems like there should be an easier, lighter way than wood. |
I've seen people (actually just pics) build skyline diffusors out of closed cell insulation foam, the rigid kind, but I have no idea whether it works or how effective it is.
When you build a wood one and a closed-cell foam one, please post your side-by-side test results here. 
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vxboogie
pushin' record
Joined: 06 Aug 2008
Posts: 262
Location: OH
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| Posted: Fri Mar 09, 2012 4:00 pm Post subject: Re: TO#83 BBC Diffusors |
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| JWL wrote: | | When you build a wood one and a closed-cell foam one, please post your side-by-side test results here. |
Hey now, that's not fair! You're the "The acoustic treatment experts"   
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Mark - Listen, turn knob, repeat as necessary... |
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JWL
carpal tunnel
Joined: 02 Apr 2006
Posts: 1537
Location: Portland, Maine
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| Posted: Fri Mar 09, 2012 6:10 pm Post subject: Re: TO#83 BBC Diffusors |
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| vxboogie wrote: | | JWL wrote: | | When you build a wood one and a closed-cell foam one, please post your side-by-side test results here. |
Hey now, that's not fair! You're the "The acoustic treatment experts" |
LOL, this is true. And as an expert, I generally stick with known materials that are proven to work. 
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