In an ideal world, every channel would have an array of thousands of individual speaker drivers, each independently amplified and carrying only a single tone. The fewer tones any driver has to produce simultaneously (and the less load on any amplifier), the better chance of reproducing beautiful, pure tones.
Unfortunately, this ain't gonna happen. The sheer cost and complexity makes this just about impossible. Not to mention the second aspect: The human ear probably couldn't appreciate the fidelity anyway.
The second best option: Each channel has an array of independently amplified drivers, but each driver must produce a range of tones, instead of a single tone. Most configurations would use three types of drivers, each optimized for a different range. A driver for the high range might commonly be referred to as a "tweeter," etc. This is still too expensive and complex for most of us.
Third best: Each channel has either a single driver or an array of drivers for each of three ranges: High, mid and low, with each range independently amplified. The exception would be the LFE channel, which -- although independently amplified -- would not need high or mid-range range drivers. Some of the very top-end audiophile speakers do precisely this, but it's still too expensive for most of us (sixteen channels of amplification for a 5.1 setup? Wow.) So we have to compromise a bit further.
More likely: Each channel has drivers as above, but only one amplifier driving all three ranges. The amplifier must be extremely powerful to drive all frequencies simultaneously at the required volume levels without distortion. Aesthetic considerations aside, it still costs too much for many of us to afford at least five (nowadays six or seven is common) full-range speakers and powerful amplifiers, plus the LFE amp/subwoofer. For many of us (including you and me, Thinkly) still more compromise is required.
Common HT setup: Some or all of the full-range channels divert their lower bass signals to the subwoofer, in addition to the LFE channel the sub is already carrying. This reduces the load (and price) of the amplifiers and speakers producing those other channels. It adds a corresponding load to the amplifier powering the subwoofer. Also the increased complexity of the multiple signals being sent to the single sub makes it more probable that the tones will not be as "pure," (the fewer tones per driver, the better, remember?) Unfortunately, this is the best many of us can afford.
The number of channels sending their bass to the sub depends upon the type and quality of each person's speakers and amplification! You send as much to the better components as they can handle.
For many people this means all small speakers and a big powerful subwoofer.
In your individual case (mains with 12" woofers, and an 8" sub): to me, it makes sense to let the 12" mains take some of the bass load off the 8" sub, assuming your main channel amps can handle the full frequency range load.
And in my case (mains with 15" woofers, twin 10" subs in a single cabinet, and good amps all around) I took the slightly unusual step of not using a dedicated LFE subwoofer at all. The whopping main woofers handle the bass from each main channel, plus they split the center's bass, plus part of the LFE. The 10" subs take all bass from the four (7.1) surround speakers (three channels), plus the rest of the LFE.
All the configurations above follow two technical principles: Let each driver handle as few tones as possible; and send the most bass to the speakers and amplifiers best equipped to handle it.
And finally, filter the technical aspects through the ergonomic and aesthetic rule: Which option sounds best? I tried at least three "bass routing" methods that I recall before finally settling on my present configuration. And if I ever get a really good subwoofer, you can bet the LFE goes back to it! :)
Hope this helped. I didn't mean to write a book...
-Bruce
This message was edited by Bruce Burson on 12/20/01 05:56.12.
