blairl wrote on Sat, 22 May 2004 12:25 |
Do you have a program to calculate the well depths of a 2 dimensional quadratic residue diffusor?
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That's easy to calculate by looking at the chart in Everest's book, but I guess a spreadsheet would make life easier. Maybe I'll make one in Excel if I have nothing to do one of these days. A small one based on the prime number 11 would have depth proportions of 01422410. The specific depth and width of the wells depends on what band you want it to be effective at. You can take several of these small ones and in turn make those the wells for a large one of the same proportionality and you'll have essentially a multiband diffusor called a diffractal that will diffuse over a larger portion of the spectrum.
As for dimensions, everybody has already mentioned the modal calculator and optimum ratios suggested by researchers. There's a visual aid in several acoustics books, Everest included I believe, that looks like a little amoeba on an X,Y grid where you can see if your planned room ratio fits into the range of desirable ratios. You can also search for Bolt, Sepmeyer, and Louden and see what they have to say. If you find a Sepmeyer or Louden ratio that also falls into bolt's "amoeba", you're probably off to a good start.
As for splaying walls, there are many reasons that room geometries more complex than rectangular are a good idea,including control of reflections to make a RFZ at the listening position. While it does alter how the room modes behave, it's not a cure for them. Some will say it doesn't eliminate them, just makes them harder to predict. While this has merit, I still wouldn't design a perfectly rectangular room including a flat ceiling. Splayed walls can help to diffuse the modes a bit, help control the early reflections at your listening position, and eliminate flutter echo.
If you splay walls (and ceilings - that's a subject for later), keep the room symetrical and when figuring out the ratio, you can estimate by calculating for a room of the same volume. In other words, if the room is 10 feet wide at the front wall and 12 feet wide at the rear, calculate for 11 feet as the width and you'll be in the ballpark. In the end, if you want to really get a handle on it, you'll have to take measurements in the room once it's finished and treat it accordingly.