need help-how to build sound absorber, deffusive

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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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.

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.