Disclaimer: acoustics is a subject upon which I am very ignorant.

So, if anyone knows of any good links for a general and informative introduction to the subject, it would be pretty cool if they could be given to me. But, that's not what this post is about.

How much affect on the overall sound quality of a home theater does it make to have subs built into the front speakers and/or center channel speaker? For example, would someone be missing much in terms of performance opting for a combo of Definitive Tech's (http://www.definitivetech.com/loudspeakers/loudspeakers.html) BP10s plus woofer instead of BP7002 plus the same woofer? If you were to go with even higher quality speakers, such as the BP7000SC, would you even need a stand alone sub? Also, since, as far as I know, bass frequencies are generally non-directional, why would it be important for a specific channel to have its own sub?

Many people use smaller speakers for the mains and center and a separate sub (or subs) for reasons of style or cost, and because a surround sound receiver is able to route low frequencies from the mains and surrounds to the sub.

Low frequencies are hard to localize; with a crossover of 80 Hz or so you really cannot tell where the sound originates. The higher frequencies in the explosion for example cue the ear as to location.

I have full range towers (sealed) with a fairly flat response down to about 40 Hz and usable response down to the 30s. For classical, piano, jazz and vocal music this is more than good enough. Never the less I added a sealed 12" subwoofer (350 Watts) for movies. As it happens a good compromise location for the sub is next to and just forward of one of the mains. That suggests that with more capable mains I would not need a sub (in the my room with my listening habits).

All of that said, I have four matching tower speakers and I've tried using them as the mains and the left and right surrounds, setting them as "large" in the receiver setup. This in my opinion produced a fuller and smoother sound field. But using small surrounds and relying on the sub for under 80 Hz does not sound shabby and that in fact is what I've done.

If all of the drivers and amplifiers are the same, buying the subs as separates will give you more flexibility in placement, and that may or may not get you a better low end response.

Although perceiving bass/subsonic audio may be non-directional, if the LF is being sent to a channel, and the speaker cannot reproduce it, that's not good. I don't buy the non-directionality thing - it's obvious in jazz where in the soundstage elements like upright bass, kick drum, etc are located.

You may find it better for your setup and budget to get small loudspeakers for front/center/surround(s), and use bass management to send LFE to the sub(s).

- Steve O.

You raise an interesting point about our ability to pinpoint the source of low frequencies. I think that a human's inability to localize very low frequencies is pretty well established as is our relative insensitivity to very low frequencies. The problem of course is defining what is ment by low and whether we are dealing with 6 dB slopes or 12 or more dB slopes.

In the case of the kick drum for example, the fundamental is actually not very low; around 60 to 80 Hz with the slap at about 4 k Hz. The lowest note on a string bass is about 40 Hz. The lowest note on a concert piano is about 27 Hz

On an inexpensive home theater setup (small satellites w/ cross over points >100 Hz) what will we hear?

The kick drum splap and first harmonic of the fundamental will come primariliy from a satellite. The fundamental will come mostly from the sub. This is easy to distinguish--the sound stage will be unrealistic.

The string bass fundamental will come from the sub and the harmonics will be split between the sub and satellites. This is harder to hear.

The piano fundamental & first harmonic will come from the sub. Higher harmonics from the satellites. This is very hard to distinguish.

Of course music (other than some electronic music and a bit of organ music) is almost entirely above 40 Hz and mostly above 100 Hz.

When the San Francisco Symphony moved into Davies Hall, the acoustics were very poor. The very large pipe organ behind the stage sounded like a small organ. The solution was to install (believe it or not) a large subwoofer assembly in the ceiling well away from the organ pipes. The music critics and audiances never noticed that the lowest notes on the organ were originating from a point above and behind the first rows of seating. But again this was for the bottom octave.

As you say sending LFE to speaker that can't reproduce it is bad, but here the questions were is it better to have separate subs and do you need a sub on each channel?

Theory and experience suggest that a system with mains able to go below 80 Hz and crossover at 80 Hz or less (with a 12 or 24 dB slope) will fool the ear as to the source of the lows, and not smear the soundstage. Whether having full range mains will sound better than using a separate sub is going to depend upon the room and the program material. In my opinion the cheif reason for having separte subs is the ability to change their room placement for smoother response. If that is not an option then I see no reason to have separte subs. There may be lows in the surround channels; certainly there is information above 50 or 60 Hz. If I could I would use full range speakers for the side surrounds, but again, it is not critical.