How to blend stereo subwoofers seamlessly

The first step is to locate the best position for your seating and for your subwoofers. The main issue, after finding where the subs work best, is getting them to blend seamlessly with your main speakers. This tip assumes that you've already located the best position for your main speakers and that you are voicing the subs for the overall combination of best blend and best bass.

Apart from voicing issues that have already been covered, there are two other difficulties that you are likely to encounter:

(1) The first difficulty can occur when the subs are simply too far behind the main speakers. That will introduce a time arrival/phase problem, especially through the crossover region. It manifests as thinness through that area, due to phase cancellation of the frequencies that are shared in the crossover region between the closer main speakers and the more distant subwoofers.

If, after going through the voicing procedures, there is still a lack of cohesion, you may need to modify the optimal position a bit so that the sub isn't too far away from the main speakers. You definitely should experiment with polarity and crossover frequencies on the subs as was mentioned in Tip #35 . Many good subs have a 0-180-degree phase/polarity switch. The most useful of these types of controls actually have a continuously variable phase control.

(2) The second difficulty can occur when the crossover frequency is too low for vocals to be effective voicing tools. This also depends on the crossover slope (how steep the roll-off is for the subs and mains). For example, a third-order, 18 dB/octave slope is more abrupt than a 6 dB slope. With steeper crossover slopes at lower frequencies, vocals can simply be too high to be totally reliable, because the steeper (sharper) slope attenuates the vocal region too quickly.

Although I expressly mentioned using vocals for subwoofer voicing, in this case, if you've done all you can with phase/polarity, sub location distance (when compared to the main speakers), and vocals, but there's a lack of palpability of instruments that have certain fundamental notes in the crossover region, I'd select a few recordings that featured solo instruments that play in that specific frequency region. Usually, I find cello pieces work the best. This issue is most often encountered with lower crossover frequencies (below 100Hz) and faster crossover slopes.

Play the passage you've selected, and, using the voicing info you've received

here, work on fine-tuning the transition between subs and main speakers. You want to see if you can get a bit more body on the cello.

When this is accomplished, you'll need to go back to your vocal references to make sure that you didn't go too far and now the sound is too thick.

To be sure, there's a blend of art and science in this area. It's sometimes a bit frustrating as you try to satisfy all conditions. Your room can play a MAJOR role in this area. Occasionally, you'll have to give up the best location for the subwoofers, because, although they are playing great bass, the sound simply isn't sufficiently seamless through the crossover region. In that case, you'll have to reduce the subwoofer/main speaker distance differential to obtain the most seamless balance and "they are here" sonic presentation.

Once you get it right, the rewards are immense. Plus, you'll have the satisfaction of knowing that YOU did it.

Jim Smith

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