need help-how to build sound absorber, deffusive

Take a look at Jon's website. He's a degree'd EE, works in Pro Sound for a living and is quite well versed in acoustics. I've built a few different pieces following his instructions and they have turned out quite well. Sean
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http://www.geocities.com/jonrisch/index2.htm

Nelson Pass with pass labs has an interesting design patented that is a microphone that measures the standing waves and then sends the signal to an amplifier that creates and out of phase waveform through a loudspeaker to cancel out the standing wave. I don't know how much the quality of the sub driver used would matter but aside from possibly being more effective than passive bass traps (ASC and hemholtz resonator types), it may actually be cheaper than the commerical bass traps (unless you build your own Bass traps). I've built the Risch traps and couldn't tell much of a difference in my room. It should be under passlabs diy section under that patents.

What are the dimensions of your room? You could have a standing wave problem that is very difficult to correct with absorbers and diffusers. Most absorbers do not work well below about 80-100Hz (even the so called "bass traps"). If you have room that is square, or 2 dimensions are multiples of each other you could have a pretty serious problem that needs to be corrected electronically. I would get a radioshack or other sound pressure meter and measure the room (and speaker) response first using something like Stereophile's test CD. Once you know what frequencies are giving you the problem, it will be easier to figure out how to deal with the problem.

Not only is placement critical when using bass traps, size and construction definetely come into play. The bigger that you can make them and the better that you can seal the "center chamber", the better it will work for lower frequencies. You might also be in a situation that requires quite a few traps depending on speaker placement and room size. Sean
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Sean's advice is good, as usual, but I'd say it's imperative to read F. Alton Everest's "Sound Studio Construction on a Budget" (which covers all kinds of rooms, listening rooms in particular). He believes in diffusion, not only absorption, and that has worked beautifully for me. If you can go the DIY route, I have instructions for DIY RPG-style diffusors and Argent Room Lens copies that I could email or snail mail to you, but you'd need a table saw for either. But if you don't yet know what an RPG-style diffusor is, read Everest first. Jon Risch's bass trap looks trickier to make, to me, than a perforated panel absorber, details in Everest. You can turn your bad room into a good one, in all likelihood. Everest also shows you how to identify resonant modes that may need to be "trapped", minimized, by bass traps or panel absorbers. That book, like his 4th edition of "The Master Handbook of Acoustics" is must audiophile reading, IMHO.