Subwoofer Frequency Response question

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

It could simply be room modal - this will not go away no matter where you
place the sub. Your only hope would be to add plenty of bass traps and EQ
down the peaks to make the trough relatively less big.

It also may be caused by your speakers - as the bass is omnidirectional it will
reflect off the wall behind the speakers. You get quarter wave cancellation
across the entire room.

Are your speakers on when you make this test? Or is it just the sub playing?

Just in case - perhaps I should explain what you should do with speakers...

You should try to avoid middle ground - either place your speakers within 1 M of a wall or more than 2.2 M to help reduce this problem. there are formulas to work out at what frequency you will get cancellation - remember this applies to the ENTIRE room. I put my large full range speakers into a soffit mount - only this way you can completely eliminate the problem - that is what studios do. I leave my surround satellites within two feet from the wall (they roll off at 60 Hz).

I quote from Genelec

For large loudspeakers, with very
low cut-off frequency (Active 3-way and Large systems), placed away from
the wall the necessary distance is far too long for any practical rooms. The
conclusion is that large loudspeakers should not be placed free-standing but
flush-mounted to perform in the best possible way.

The cancellation frequency is Fc = C / 4 * D.

D= Distance from front baffle of speaker to rear wall behind speaker.
C= 344 Meters/sec
Fc is in Hz.

In your case a suckout at 45 Hz equates to a Distance of 1.9 meters. And 70
Hz equates to a distance of 1.2 Meters. If your Europa speakers are in
between these two limits then it could well explain your problem. Typically
this yields a 20 db suckout. Most people have this problem as they use large
full range free standing speakers. Since most people ignore it - even a 20 db
suckout - as bad as it seems - is it not likely to ruin your enjoyment of music.
Sometimes other room modes can compensate at the listening position.
Hopefully you can see that speaker position can be important too - not just
the sub.