[Wayne A. Pflughaupt]

lovingdvd wrote:

The one thing I am still confused about is that I keep reading remarks about how the main and sub interact at the crossover point. However in my case they interact far lower than just a the xo point.

What that refers to is response changing around the crossover point once the mains are added. Typically it’s a phase issue introduced by the crossover. Response deviations that appear with the addition of the mains can show up as far as an octave above or below the crossover frequency.

For instance my mains are rated to 32dB and even though I have the xo set to 80hz and the mains set to Small, I still get say 30-40dB of bass below even say 60hz when using 75dB as a reference. I don't quite understand this but apparently the slope is a lot slower than I would have thought. For example I would think (for no particular reason really) that with a xo of 80hz there'd be nothing much coming out below 60hz of my mains, but this is far from the case.

You have to keep in mind that the crossover’s slope is subject to the acoustical output of the speakers, as well as the frequency response of the source signal.

For instance, let’s say your speakers have substantial bass output and do a 6 dB/octave rise between 100 and 30 Hz. Your receiver’s high pass is rated at 24 dB/octave. So, what you end up with is a functioning roll-out of about 18 dB/octave. The same thing will happen with room modes that cause a peak in response at say, 40 Hz – instead of being more than 24 dB down (assuming a 100 Hz crossover), it might not be more than 12 dB down, or even less, if it’s a really bad peak.

The other issue is the exaggerated bass response that action movies have. An explosion that gives a 20-dB boost below say, 30 Hz is going to essentially reduce the crossover to near-flat response.

A good way to see if your crossover is working to spec is to play sine wave tones at the crossover frequency, and an octave lower, and measure both with a SPL meter. The lower-frequency sine should be in the neighborhood of 24 dB lower (or whatever your slope is).

Regards,
Wayne