Room or speaker resonance???

Was there a reference tone at around 1000hz(or there abouts) so you could set your volume control for a 0db reading on your SPL meter? There should have been. Work you way down from there at 1/3 octave intervals for a better idea of your actual room interaction(IF those frequencies are available on that disk). Generally reverb nodes/nulls will show up at multiples of a given freq., ie: +20db @ 40hz, +10db @ 80Hz, +5db @ 160hz. The size of the room will determine at what wavelength the primary node/null shows up. Secondary reflections(floor, ceiling, side walls) will also have a comb effect on your response.

I'm sorry: I should have said, "so you can set your 0db reference on the SPL meter's 90db scale". Or 80db scale, if your ears are more comfortable there.

That's normal. Placement of the speakers within the room is super critical in the bass region. Since you've got the meter out, move the speakers a foot closer to the wall and note how different the response is.

There a nodes that cause the bass to peak at certain frequencies. Reduce the peaks via placement and you'll flatten the overall response. Trying to set the speakers using a meter is tough work, if you can get professional help, do. Many people merely pull the speakers way out into the room to null most of the nodes. (That's what I used to do). However, the best approach is to optimize bass performance by using the nodes, but it's much easier said than done.

Hopefully there'll be a DVD ready later this year to help you do this.

Dave