RPG Skyline clone
Not too long ago, I came across the acoustics DIY website of Audiovideo. Among all the projects presented, there was also a MS Excel sheet that calculates dimensions for a RPG Skyline diffuser clone. Afaik what separates Skyline from regular diffusers is that it works on sound coming from any angle and thus makes alignment with the speakers less critical. Build process seemed fairly simple at glance too: just get eg. a sheet of high density polystyrene foam, slice it to pieces according to the Excel sheet and glue these on a board. As things usually go with projects like this, it didn’t take long until I found myself thinking about giving Skyline a go.. ;)
Since the Audiovideo website is in finnish only, I’ll briefly guide all you non-finnish readers through the calculation sheet. Not that there’s much to it: The sheet has a single input field that you need to modify and this is the green one right on top!
The value to input is the height of diffuser in centimeters. At least 10cm is recommended but adding more will widen the effective frequency range of the element (more lower bass freqs get diffused). The recommended side length is 4cm. For the material, high density polystyrene foam is preferred due to its low weight. However the site says eg. wood should be just as fine if your wall mounting spot can handle the weight.
Soo.. Light-weight one it is for me! For this test piece I bought an insulation sheet 5cm thick and chose to use 15cm as the height. I’m not sure how much the extra centimeter on the side dimension affects freq response, but leaving sheet thickness as-is saved me from a lot of cutting (in comparison to 4cm). You see, what I chose to use here was a large kitchen knife.. And oh boy did I miss whatever anything else that might have sped up the cutting process! :)
The sheet was first sliced into 5*5cm bars and these were then cut to all the required lengths (total of 169 pieces!). Coming up with straight-edged bars was really difficult and I ended up tossing quite a lot of unsuccessful ones. Lucky me the sheet was large enough to complete the element. Without all the binned bits there probably would’ve been enough material for a second element.
Now if cutting was a cumbersome chore, so was glueing all the pieces together too (albeit less sweat inducing). For this part of the build I could at least sit on the sofa and watch some telly while at it. For the backing, I chose 2mm fiberboard. This proved a bad idea somewhat halfway through the glueing (pic above), as the board started flexing in when the tightly packed polystyrene bits started adding up tension. Upping the counterweight somewhat fixed this..
.. but the element turned out slightly concave on the back. After the glue had settled I added some thin metal wire on the backside. This way the element can be hung on a wall with a single screw.
Looking good and all, though maybe it could use a bit of matching paint to blend in better with the wall. If I’d have more space in the music room, I’d probably put a set of these on the wall and hang a thin curtain in front. All in all, if made like this there’s just way too much work to even consider making a bigger set. Wood would be easier here; just pick up something like 2*2″ and slice that.
One slight problem remains though: “How do I evaluate does this thing work at all?” :D