Secret to sub performance...

[Flint]

If you have two subs, which is probably overkill, get some measurement equipment/software which can quickly run in room frequency SPL curves accurately in the bass range, then go to town:

1) Measure the SPL of each and match perfectly (don't rely solely on the volume knob placement. We've learned one knob needs to be at a "higher" setting according to the dial to get the same SPL at the listening position.
2) If running a mono signal split to the two subs, then forget room symmetry.
3) Move the subs around, and measure at each position until you can get the best results. We moved one at a time and measured the results. We saved the results so we could return a sub to a location which seemed to work better.
4) Once you find ideal placements for optimal response and tonal balance, tune the crossover and distance settings to blend with the main speakers. Measure often.
5) Drink too much Scotch, turn up the music to confirm the sound quality, then put in the loudest The Who concert you can an marvel at the results until you pass out.

 

[Deleted member 133]

You probably covered this in the detail above, but perhaps stated somewhat differently...

Once you have chosen your final position(s) for the multiple subs (by finding a good location for each one as described above), turn all but one off. Balance its SPL against the entire system. Turn it off and the next one on. Repeat the balancing. Continue until all of the subs have been balanced individually. Then turn them all on and balance the ensemble of subs, now treated as a single sub, to the system (which means backing off on the overall sub level.) Each sub will now be working much less hard than if it were handling the whole load, and the multiple subs, if properly placed, should result in smoother overall room response.

Take two scotch and call me in the morning.

Jeff

 

[Flint]

Working together two non-symmetrically placed subs, the combined signal can be louder or softer, so that method won't get consistently good results. In this case, the combined acoustic performance after perfecting the placement and settings removed a huge 10dB SPL bump centered at about 65Hz, so a traditional SPL Meter measurement with receiver tones would have failed using that method. Instead, we were running quick sine-wave sweeps, then checked the steady state room excitement performance on an RTA with pink-noise and 10 sample averaged measurements. The result is a ruler flat response from 10Hz to 100Hz from the subs which we then calibrated to the main speakers, which wasn't difficult given the test tools we had at our finger-tips.