Unsound, What you are referring to did happen when people summed the L and R electrically by using a Y connector at the preamp and then running one IC with a mono amp for the sub. But if you keep the two channels separated electrically and either use a woofer with two voice coils (and a two channel amp) OR mix the channels with a buffered circuit and then use a single amp and voice coil, then that won't happen.
Whether one gains more spatial effects when two separate subs interact in the room has been debated. I suppose if a low frequency signal like cannon fire was clearly located on say the left channel, you would notice it, but anything below 120 Hz isn't very directional and I think the room would tend to soften that effect. It's the mid-bass and midrange that gives directional cues, and those are being handled by the main speakers.
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Whether one gains more spatial effects when two separate subs interact in the room has been debated. I suppose if a low frequency signal like cannon fire was clearly located on say the left channel, you would notice it, but anything below 120 Hz isn't very directional and I think the room would tend to soften that effect. It's the mid-bass and midrange that gives directional cues, and those are being handled by the main speakers.
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