Dual Subs

Am I correct in assuming that dual subs in stereo would have to be symmetrical to the sweet spot which may not, according to Duke's comments above produce the best results? Is "stereo" a big issue when it comes to low fequency reproduction or is it more an issue of placement resulting in the best sound possible ?

Byfo, very few recordings are stereo below 100 Hz, but the final answer in my opinion is related to the low-pass filter frequency and slope. (The low-pass filter is what rolls off the top end of the sub's output, and usually the frequency is adjustable but the slope is fixed.)

In general if the subs are audible as distinct sound sources (while the mains are also playing), then they're putting out significant energy high enough into the lower midrange that they should be positioned fairly symmetrically and near the main speakers. If you can't detect the subs as separate sound sources, that means they're crossed over low enough and steep enough that they can be positioned with priority given to in-room bass smoothness - and they're probably operating below the region where stereo is a factor.

As a ballpark rule of thumb, if the subs are rolling off at 24 dB per octave around 80 Hz or lower, I wouldn't worry about positioning them with stereo in mind. But you can't necessarily trust the frequency knob on your plate amp, so if your ears tell you the subs are audible reposition them accordingly.

As a rule, this is what I do to adjust the symbiotic relationship between my sub and speakers...adjust your crossover on the sub approximately to 100hz. Then, while listening to music, adjust volume to JUST where the sub is overpowering the lower frequecies of the speakers. Tweak your crossover position now. The outcome will be the optimal settings for the system. The additional sub should be adjusted the same way, and placed in referrence to the other sub and speakers. IF you want boom boom...turn the sub up and scratch accuracy. Two subs placed accordingly will creat a balanced, lower frequency field distribution, which will not exactly sound "stereo"...but will "balance" the emitted waves traveling to your ears. Subs are not directional (lower frequencies), but when used as described, will provide a tonal balance. I didn't write the book on this stuff btw...I just read it a million times. LOL.

Thanks for the clarification Duke.
Byron