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Abnormally strong sub output below 35 HZ

615 Views 9 Replies 5 Participants Last post by  ChrisWiggles
I have not plotted my results with sine waves, but did use the sweeps from Avia and my SPL meter for these results. I know this is not exact, but it is good enough for this question. When I run the sweeps, I get a pretty flat response all the way down to about 35 Hz where the needle only swings 2-4 dbs at most. From about 35 Hz down to about 22 Hz, the needle jumps up dramatically (about 10 to 15 dB's and that is not even corrected values). I believe this is either from room gain, or a peak in the room.

Here is my thinking... Tell me if I am off here. I have read that most music doesn't go much below 40 Hz anyway so it shouldn't affect music that much. If you were me, would you count your blessings, and be happy about the peak for movie effects, or would you find a way to drop that number down to be more flat?

To my ears, music sounds right, and movies have big impact. I am happy, but I don't have much experience with subs, and am not really sure how much bass is too much bass for music since I have listened to music my entire life without a sub until about the last year.

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Big question, and one I'm dealing with right now. My peak is about 32 Hz, with a double at about 64 Hz. (Might be a 16 fundamental, but the test doesn't go that low.) We've got standing waves in our room. In other words, the rooms have natural resonant frequencies that are excited by the subs. That means that there are nodes and nulls in the room, too: spots with lots of signal and spots with very little.

There are two approaches that I know of to deal with it. 1) equalization, that massages the signal to chop down the peaks. Unfortunately, I don't think EQ can do much for nulls without overdriving the sub. 2) Room treatments to absorb the resonance. These are tough to apply if you don't have a dedicated HT room.

People that know a lot more about this than I hang out in the Audio Theory section. Best take it there.
Maybe this will help with your room problems, a Behringer Feedback Destroyer.
I have to have 5 post to submit links so bare with me.
Originally posted by DMF
Unfortunately, I don't think EQ can do much for nulls without overdriving the sub.
But you guys aren't talking about a null - but just the opposite - a resonance. An equalizer is perfect for this. You'd want a parametric equalizer so that you can set the exact center frequency and adjust the width (i.e. Q) of the filter.

With a standing wave you have nodes (strong points) and nulls. Between my peaks I have some serious dips, although placement does make them better in some places than others. Redskn said his was essentially flat, so he probably has found a good location. But in most setups there are going to be nulls that are nearly impossible to overpower electronically.

Don't get me wrong. I may well end up with an EQ, but it will be because my room isn't dedicated and I can't apply serious LF treatments.
corner bass trapping is a good idea to do before BFD, though certainly EQ can help. Room treatment is ALWAYS a good idea, and can get at the root of the problem rather than a band-aid of EQ, if you have to choose one or the other. Good treatment, plus good placement, plus EQ is the absolute best.
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