Home made Skyline Diffusors

I came across a BBC research paper that shows the design of skyline diffusor (the BBC reports are a goldmine of info!) These things cost $280 for 2 from RPG :shock: - but with the BBC design in hand I'm figuring you can make them yourself for about $50 each using balsa wood blocks which should be light enough to hang on the ceiling. Balsa blocks 2x2x12 are $1.04 each - these can be easily cut to size. Each unit would be 2ft x 2ft x 8inch high max. I made an excel file - it has the grid taken from the BBC report - the report doesn't show height, but has 0,1,2,4 in the grid boxes. So assuming 1 = 2 inches, = 8 inches max height, which is the same as the RPG ones which are also 24x24 dimensions. Can't attach the excel file - if you can add xls to the allowed upload files I can attach it. Cut to size, then glued onto a thin sheet of ply with modelers cement - then either varnish for a cool wood look or spray paint with enamel. :D You could even make them 4ftx4ft - would increase the price a lot, but would be even better at diffusion of low frequency. I figure these should be just as good as the RPG ones and heck it's always a lot more fun to make it yourself than buy it. :) Another option instead of balsa could be polystyrene blocks - could be a bunch cheaper, but couldn't yet find any suppliers on the web

This was covered to death over on homerecording.com -- http://www.homerecording.com/bbs/showth ... hlight=diy John, please let me know if its out of line to link over there. I figured since you were a part of that discussion it would be ok... -lee-

No that's fine lee - saves us all posting it all again. :) cheers john

Interesting thread - although they are on a track of making it out of highly flammable PVC pipes and worrying how to seal the ends :shock: I'm no where ready to be sidetracked on these things - but diversions are fun. I went out and bought the stuff - using 2x2 furring strips - and a 2ft x 2ft backer board - total cost $16

One thing I can't find browsing through that HR thread is whether the wood density would matter or not? Would two diffusors built precisely the same way, but one in balsa and one in MDF, act differently? Cheers /Henrik

AndrewMc wrote:

Interesting thread - although they are on a track of making it out of highly flammable PVC pipes and worrying how to seal the ends :shock:

Yeah. Like balsa wood's not flammable. :roll: I think you have a good idea, but I question wheather the balsa is dense enough or not. Or even if it matters. The price you gave for balsa: Is that 2x2x12 INCHES, or by 12 FEET? You could buy a piece of 2x2x10' stock pine at the lumber yard for a couple bucks and not have to worry about the density.

I don't think the density much matters as the purpose is reflection. If it absorbed sound then I think it would be an issue. The main thought about Balsa is that it is light - so would be easier to put on the ceiling. The size of the balsa is 2x2x12inches. I made a prototype using pine - real easy to make - cost $16 in total but it's a bit heavy, am planning to make a balsa one too.

Wow, Andrew, looks great! So this is based on the calculations from the BBC paper? I'd very much like to see the Excel file you made. If you like, you can email it to me, and I can make it available through my web site. [removed] . Cheers /Henrik PS John, I don't ever get the email notifications when a reply is posted. Yes, my email address has been entered correctly, and yes, I checked the option "Notify me...". Is that a problem you're aware of?

PS John, I don't ever get the email notifications when a reply is posted. Yes, my email address has been entered correctly, and yes, I checked the option "Notify me...". Is that a problem you're aware of? _________________

I've contacted Peter about it. Thanks for pointing it out ;) cheers john

Henrik wrote:

PS John, I don't ever get the email notifications when a reply is posted. Yes, my email address has been entered correctly, and yes, I checked the option "Notify me...". Is that a problem you're aware of?

me neither :(

Henrik - the BBC paper is at this URL http://www.bbc.co.uk/rd/pubs/reports/1990-15.pdf it has the layout. The excel file is just to make quick calcs on how much it would cost using different materials. The BBC reports are a goldmine. There are some very interesting articles on experiments for noise loss thru different types of walls that shows TL at different frequencies rather than just STC.

OK, thanks. So if I understand this correctly, you made the simplified version, the one that diffuses up to 3.4 kHz? So do you or anyone else know how big the difference will be making a more compiclated diffusor, that affects a wider band of frequencies? I mean, is it worth the effort? Cheers /Henrik

Yes - I made a copy of the BBC prototype. They mention in the report that the actual frequency range was greater than theory. From reading the report - they mention that the width of each element impacts the high end & the max height impacts the low end. The RPG ones are a very similar dimension - although instead of 12x12 they are 12x13

OK, cool. I'll try it myself some day. It DOES seem a bit tedious to make them out of 1156 17 mm wide pieces of wood...

Hello all - I hope it's OK to wake this old thread up! I've finally reached the point where I wanted to try building a couple of BBC Diffusors myself. (I guess the idea needed to mature for a while, haha). There is one thing I'm not quite sure I grasp from the BBC paper: Do they say that placing several of the prototype diffusers side by side may not be a good idea, creating unpredictable results? I'm asking because I often see whole walls in studios that are covered with diffusors of this type, and I wonder if doing so using the BBC prototype may yield some unwanted results? Cheers, Henrik

great thread does Balsa have sound-absorbing properties? i read the rpg skyline page and it shows an uneven absorption for the styrofoam versions they sell. PVC won't burn by itself, it's self-extinguishing, or so i was told when remodeling part of the club i work with recently.

Here are some photos of my custom built rear wall diffuser.

oh my good word, that looks so rad. How much did that beast run you?

It cost me close to $800.00 US.

Whoa - that looks incredible. I bet you were relieved when you stuck in the last piece of wood !

Ditto WHOA! Are those based on the BBC prototype module, or how are they constructed? Cheers, Henrik

The diffuser was designed and constructed by me by lag bolting a 2" X 6" PT frame to the concrete wall then two 3/4" sheets of plywood were doubled up and attached to the frame. Next, Douglas Fir balisters were compound mitered to varying degrees and lengths to achieve diffusion. I had to constantly adjust the balisters to give desired results read through my trusty Agilent 8594E 3 GHz spectrum analyzer. Once the desired configuration was found, I removed the diffuser from the wall laying it flat on the floor then glued and brad nailed each piece. Be patient, the diffuser construction took about a month.

It looks beautiful, great job! I've been in touch with a wood firm (or whatever they're called in English), that said they'd be happy to cut up all the pieces for me and sort them in different boxes. So I'm thinking of doing that, and then just trusting the BBC papers. It will surely be a lot better than the diffusing panels I can afford. I'm counting on cost being something like what you mentioned, 800 USD. That's for 14 BBC panels, 600x600 mm. Cheers, Henrik

[quote="Brent Jason"]i read the rpg skyline page and it shows an uneven absorption for the styrofoam versions they sell. [quote] Is this good or bad? I thought about doing this with styrofoam. Seems like it would be the easiest way to go.

I think this is a nice little web site... does this help anyone? http://www.mhsoft.nl/DiffusorCalculator.html I would love to build some of these when the time comes... Cheers Steve