need help-how to build sound absorber, deffusive

Ltt:
Your dimensions aren't too bad. You probably have a bump around 40 Hz, but I doubt it's so serious that you can't tame it (at least most of the way) with passive devices. I would still recommend that before you begin, chart the frequency response and find out how bad the bump is. Then you can see how effective any changes you make are. The measurements don't replace listening of course (and sometimes a flat response sounds just like that--flat--not involving), but I would still do it to have an objective measure to help guide you. Once you get close to eliminating the bass problem, you will need to fine tune things with your ears, not with measurements.

Sean-
My room is rectangular-14'x24'x7.6" and my speakers are B&W N. 802. The speakers are 4' from behind wall, 3'from the side wall and 9' from listening, one wall has a window with with a curtain cover. The other wall leads into a hallway. There is a bay window behind listening. I tried to place the speakers farther away from the walls but the bass didn't get any better. Besides fiberglass instulation being used for sound absorbing and deffusive, is there any other material to use? Thanks.

I agree with Tom on every count except for making Jon's bass traps. They really aren't that difficult.

A well balanced room is no different than a well balanced system. You can't concentrate on one aspect and neglect all of the others hoping that everything else will fall into place. As such, you need to use a little diffusion, a little absorption, etc... as the room and system needs it.

Keep in mind that two rooms of the same exact dimensions might be set up quite differently though. The overall layout and what is needed in terms of absorbers, diffraction, etc... will vary depending on the type of speakers, their placement and their type of radiation pattern.

With that understood, i once again stress that there is NO universal formula that will work in all situations ( just like speaker placement formulas ). Without personalized data on the specific situation, nobody can tell you how a room should be treated. Most of it will boil down to common sense and quite a bit of trial and error. Sean
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Tom-
I have a table saw and other tools. I'm willing to try anything, but please try to keep it simple because I'm not great with following instructions!! Please email me at LTT142@aol.com. I appreciate the help. Thanks.
Lac

Here's help:

http://www.decware.com/acintro.htm

Keep it simple...

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.

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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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.

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.

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