I made it through the first sentence then my brain started to melt a little.
I understand the end result it's the process behind it that causes me pain. The only thing crossing right now are my eyes... I've got a lot to learn.
I'll re-explain in easier terms for you. I'm sorry if I was in a hurry and did not make it very clear. My previous statements will be italicized, to be followed by a better clarified version.
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You must also use an active crossover to high-pass the signal to the satellites and low-pass the signal to the subwoofers."
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High-pass means the frequencies over the xover point. So, if you cross at 80Hz, then this means frequencies over 80Hz pass to the speaker. Low-pass means the frequencies under the xover point. So, if you cross at 80Hz, then this means frequencies under 80 Hz 'pass' to the speaker.
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For HT use, one is fine. But a dramatic increase in SQ is the normal result with proper stereo subwoofers when music is the main priority. With twin units, one can get idea/seamless/perfect integration of the subwoofers and small main speakers resulting in full range 3 way SQ/integration quality."
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HT(home theater) is not as demanding for sound quality. Movies do not have the same level of realism as do the high quality music recordings. Movies have the priority of special effects reproduction and center channel dialogue reproduction clarity as the most important factors. This being the case, you also do not need the same level of seamless bass transition from the main L and R channels to the subwoofer/low bass. But a very powerful, very deep bass is very useful for movies to fully create the huge range of low frequency effects present in modern movies. Music needs more coherency where the deep bass transitions to upper bass (the region where you cross over subwoofer to L and R mains) due the focus not being special F/X, but instead things like drum sets, bass guitar, cellos, etc as the primary sounds in this range. Because the physical lengths in air of these frequencies(at and around xover point) being to become short(relatively), it's difficult to get the waves (i presume you are familiar with basic wave physics, etc.) to sum to target unity at both main speakers from a single sub at the same time unless the sub is in the worst possible place(center of front wall between main speakers) where it will have the lowest ouput SPL and worst response possible(very very rough frequency response) due to this room position.
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If you are crossing very low (40-50Hz) with an aggressive filter rate (24db/octave or steeper) in a medium to small size room, then ignore the above info."
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40Hz, for example, has a relatively long physical wavelength. As such, this makes it much easier to get the subwoofer to sum to ideal target response with both main L and R speakers at once even when the subwoofer is located on the extreme one side of an averaged sized room(this is of course not true if you have a HUGE room dimension and have the speakers positioned along the width of this HUGE dimension; 25' or larger could be defined as huge for purposes herein).
One question I can ask now though;
If my time is split 80/20 movies to music but my speakers are lacking in the lower ranges would it be better to go with two smaller subs instead of one large one?
Pay attention to the xover frequencies I mentioned earlier. For music, two subs are superior (one sub placed on each side of room), no question, if you are crossing around 70-80 Hz. If you are crossing around 40-50Hz, then one single larger sub will be fine. Only full size speakers with substantial bass output should be crossed at 40-50Hz. Two way speakers using 7" or smaller mid-bass drivers should be crossed at 70-80Hz, or even 90Hz, to relieve the drivers of most stress, thus allowing larger, more clear dynamics. Hand over the LF to subwoofers - but two subs would be needed for seamless sound transition for music. For movies, it just does not much matter if you have one or two subs, so far as the seamless effect - as movies primarily deal with special F/X bass.
-Chris
