[bkspero]

First, I would like to thank everyone who contributes so much time to this forum, and particularly to the gentleman who wrote REW. I am amazed by the power of the software and the amount of information on this site. My son and I have been lurking here and at a few other sites for about a week, and I think that we understand enough to ask reasonable questions.

I will paste some photos into a later note in this thread when I figure out how to shrink them enough. For now, please indulge my wordy description. We have a small single-room home recording studio that is also used for mixing and mastering. And we're trying to use REW to help optimize the sound during playback. The room is 11.8 ft x 13.5 ft with an 8 ft ceiling. The mains are along one of the longer walls about 1.5 ft to the right of center. There is a single window opposite the speakers behind the listening position, a double window on the wall to the left, and a double sliding door closet to the wall to the right. Where the back wall goes up to meet the ceiling it doesn't go straight up into a right angle, instead it slants into the room at an angle for about 10" before it reaches the ceiling. We have 2 inch foam covering much of the exposed walls, and Lernd type corner bass traps along most wall ceiling junctions (except the angled portion). We have a foam cube and Lernd traps in the triple corner at the ceiling to the left of the mains (the door is down a small hall in the right front corner. For all the discussion below, we also placed double thickness of portable fiberglass panels made by Clearsonic about 20 inches from each vertical corner (a total thickness of 3" of fiberglass board). There were also 1.5" Clearsonic panels 18 inches in front of the window opposite the speakers (covering the back first reflection point). Finally, there was a 3" thickness of Clearsonic panels about 18" in front of the closet door (including the 1st reflection point). There was 2" of foam at the left 1st reflection point. Finally, the room has a full carpet with 1/2" foam pad over hardwood flooring. There is nothing on the ceiling. The room is amazingly quiet and "dead" (in a good way, I hope).

Speakers are Mackie 624 mains and a Mackie 12" sub (downfiring active and front firing passive driver). Mains are set about 50" apart and the back of the speakers are about 10 inches from the front wall (just ahead of 2" foam panels). The sub is located on top of 1" heavy foam on the floor just to the left of the left main (without the foam the floor resonates like crazy at 20-25 Hz). The mains are on stands with the tweeters about 53" above the floor. The mains are angled to meet just behind the head of a listener located midway between them and 38% away from the front wall.

We have 2 problems. First, the bass response has some severe valleys that we can't seem to correct no matter what we've done with sound absorption or speaker placement. Second, frequency response is very sensitive to small shifts in listening position, even movements of less than a foot can have drastic effects.

I have attached some graphs showing the problems. All include both the sub and mains. The crossover is set at about 90 Hz. The first graph shows the sensitive dependency on position. It compares four positions within a foot of each other. Red is the normal listening position (38% from front wall midway betw. speakers), green and blue are 1 ft behind and 1 ft ahead of that along the midway axis, purple is about 8 inches to the left of blue. Is this normal? Any suggestions on how we can widen the listening region.

The 2nd graph shows the problem we are having smoothing the peaks and valleys at even the normal listening position. We thought that the valleys were nulls and the peaks resonances. So we thought that if we changed the sound level we would be able to change the peaks without changing the valleys (our reading here taught us that nulls don't respond to sound level, since both the primary and reflected waves change in the same proportion they continue to cancel to the same degree...that's why one shouldn't try to Eq up a null). But the 2nd graph shows that a 4 dB increase in sound level raised all portions of the spectrum about equally. We have a dozen more graphs showing different sub positions, speaker positions, sound absorption configurations, etc. without getting anything better than this. We would appreciate guidance as to what could cause this, and how to fix it. We would prefer treat the room and not use a PEQ, because the room is used for recording as well as playback, and the PEQ won't help with the recording.