Subwoofer Frequency Response question

Your going to need to get a better handle on whats going on, before you can attempt to fix the problems.

If your going to try the spl meter route then you will need a good cd, or a computer with test tones on it.

For free go here: http://www.realtraps.com/info.htm

You can download the test tones and burn them, or use them direct from your computer (better, because you can loop them). These are better than most because they cover more range, one db at a time (you can read about them first). There are some other good tools at the site also...and plenty of good reading.

I usually start with the main speakers only, and then I move to the subwoofer only.

And then move on to some crossover settings, that I think will pull the two together, as one. Kind of a divide and conquer approach in the first two steps, or at least a better understanding of the problem.

The "Virtual Minirator" download is another good tool for your computer.

I suspect you need a lot of bass traps in that room, but hey...what room doesn't :-)

Dave

Thanks for all the suggestions. I am using the Rives CD with 1/3 octave tones calibrated for the RS Meter. I am going to check out the realtraps site. Using this, I was also able to find a wire vibrating inside the speaker at mid-range frequencies. A little Blu-tak and voila! No more vibration.

PDN - Measure test tones with the meter in dB then graph the test tones and you will determine what your response is in a given frequency range.

I took readings with and without the sub and with the subwoofer by itself. This really helped clarify what was going on (thanks Dave). I was clearly having phase cancellation. After tweaking the settings on the sub and taking readings at various settings, I was able to eliminate the dropout at 50 hz and get a fairly flat response. The exception is at 35 to 40 hz where I have about a 10 dB increase. This seems typical of many subs and may also be the room.

Would this be eliminated by stuffing more material into the sub or external bass traps.

A 10db peak is not uncommon at all, you could eq that down. Peaks are better than nulls, you can't eq a null up and out.

Some subwoofers (they call them hometheater subwoofers), do indeed have built-in bass peak, I don't know anything about your sub though.

At any rate...you could eq that out too.

Dave

What you described, a deep notch at the crossover frequency, is the classic symptom of drivers out of phase. In fact this is the best way to find out what the crossover frequency is. Invert one driver, and look for the notch.

Most bass traps I've seen are designed to reduce peaks at 80hz upward though some provide a little boost at 50ish hz (bass busters). You can eq nulls, but it's not easy for a 20 db problem, I'd guess you might get some improvement via PEq, but not a full fix. I would have seconded Eldartford's recommendation, but it seems from your post that you've already tried that with no success.

I use a Velodyne SMS-1 x-over, analyzer, and PEq unit that is fantastic, but in your case I'm not sure what will help.

Marty