UCA202 Confusion!! - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 23 Old 11-06-11, 01:31 PM
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Re: UCA202 Confusion!!

Congrats on going to better equipment! Looks like a good sweep, and actually a pretty good overall response. No way to know if the comb filtering evident between 70 and 300 is between the speakers or due to in-room reflections, though I also wonder if your dip at 70 is due to being in the null of the first vertical axial mode.
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post #22 of 23 Old 11-06-11, 03:27 PM Thread Starter
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Re: UCA202 Confusion!!

Bob Gold output: room is 8 foot high, 13' 8" wide, and both 16' 4" deep with another alcove adding another 40". I am sitting 6 inches off-center to the right. I am wondering if since the 70hz is due to the height I may not be able to squelch this.

Freq % Wavelength, 1/2, 1/4 p,q,r Mode Group Weighting
28.7 hz 39'4", 19'8", 9'10" (1,0,0 Axial) Start iso, End iso
41.3 hz 30.5% 27'4", 13'8", 6'10" (0,1,0 Axial) Start iso, End iso
50.3 hz 17.8% 22'6", 11'3", 5'7" (1,1,0 Tangential) Start iso, End iso
57.4 hz 12.3% 19'8", 9'10", 4'11" (2,0,0 Axial) Start iso, End iso
70.6 hz 18.6% 16'0", 8'0", 4'0" (0,0,1 Axial)
70.8 hz 0.2% 15'12", 7'12", 3'12" (2,1,0 Tangential) Start iso, Near
76.2 hz 7% 14'10", 7'5", 3'8" (1,0,1 Tangential)
81.8 hz 6.8% 13'10", 6'11", 3'5" (0,1,1 Tangential)
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post #23 of 23 Old 11-07-11, 09:47 AM
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Re: UCA202 Confusion!!

I would run your room with both depth dimensions in Bob Golds calculator, as the modal behavior would be somewhere between the two. I was thinking about that in context of your L-shaped room before, but I forgot to mention it. My room, actually, acts like a combination of the the room at its natural length, and that plus the depth of the closet in the rear so while it's not as obvious I have a somewhat similar situation, though with a lot less of a dimension difference. Anyway, I knew the first mode of 8 feet is always 70 Hz; it's a very common issue. I've seen some companies specifically selling corner panel absorbers specifically tuned to that frequency even.

What you need to do is figure out if it is a mode or a reflection issue. One way I'd do this is to use the signal generator in REW to play sine waves at 69/70/71/72 Hz, and while it is dwelling on an individual frequency to move the SPL meter (or the REW mic using the REW SPL meter) around the room - into the corners, up/down/left/right from the listening position, etc. If you see and hear large variations in SPL characteristic of room modes, you have a modal issue at that frequency on your hands.

The way to find out all the frequencies at which you are likely to have modal problems I got from some guys on gearslutz: drive a small sealed subwoofer into a corner, and into another corner put the microphone. Or do the best you can anyway... at least just put the mic in a corner. Since pressure maxima of all modes appear in corners (at least in rectangular spaces, I'm not 100% sure this rule applies for irregular spaces), the waterfall/decay/spectrogram of a sweep done with this measurement position will show you all frequencies at which the room has modal energy storage, independent of listening position. Then you can correlate that information to listening position results.

Given the acoustical lengths you've gone to so far, I don't think controlling a 70 Hz mode is likely impossible. There are a number of acoustical devices you can use for damping at that frequency.
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