Choosing Sub-woofers. Please advise ASAP.

No.

"A full range speaker should sound better with a smaller sub by virtue of its FR and the fact that it’s producing decent bass on its own already. Conversely, a small speaker should benefit from a bigger sub to cover a wider range."

It doesn’t work that way. Here’s the "old school" principles:

Smaller woofers/subs are TYPICALLY more limited in extreme low frequency output than larger woofers/subs. Since the presumption is that the OP has "full range" speakers already and wishes to further enhance the ultra-low bass output of his system, the larger woofer/sub SHOULD go lower, providing more ultra-low frequency enhancement, all things being equal.

Further, if the OPs "full range" speakers already have a strong mid/upper-low frequency output, adding a smaller (higher frequency output) woofer/sub will create boominess in that range (major overlap in the midbass). Worst of all worlds IME.

Conversely, a smaller woofer/sub should TYPICALLY be quicker and more tuneful in the mid/upper-low bass frequencies, thus easier to integrate with a "smaller" speaker, assuming that the latter’s low frequency output rolls off a significantly higher frequency than a "full range" speaker (minor mid/upper-low frequency overlap of the smaller speaker with the smaller sub’s higher output frequency). Ultra-low bass will not be enhanced as with the larger woofer/sub, but that is irrelevant if integration is poor.

Many potential exceptions to this are experienced in the real world as it depends heavily on the cabinet size/design of the sub, crossover adjustment flexibility, design (ported vs sealed), amplifier’s power/characteristics/ability to control the woofer, and placement. Also the newer concept of digital room equalization/correction built into the sub’s digital electronics (a’ la’ JL Audio and a few others) negates the "old school" rules to some extent, allowing a larger woofer/sub to integrate well even with smaller main speakers by tuning/contouring the sub’s output (increasing or reducing the output at certain frequencies based on system characteristics/room acoustics as measured by a microphone and processed by the sub’s digital circuitry).

Subs can also be used for entirely different purposes than "bass enhancement". I use two REL Stadium III sub’s fed via the high level inputs from my amp with the subs’ crossovers set to "out-of-phase" mode to cancel standing waves due to room bass nodes, actually reducing the perceived bass heard at my listening position, and to enhance the soundstage (by loading the room with sound pressure from the subs) as my main speakers need no low-bass enhancement, but actually the opposite in my room. Works quite well.

Dave

Hi Tim,

Glad to give it a shot.

What I said was that I use the RELs out-of-phase to cancel standing waves due to room bass nodes. The improvement in soundstage happens due to the sub(s) loading the room with sound pressure, either "in-phase" or "out-of-phase". Works both ways if your sub(s) is capable of true ultra-low frequency reproduction and the crossover is set properly (at the lowest crossover frequency setting in my case).

To set up the sub(s) for soundstage enhancement, adjust the crossover frequency and output levels so that the bass enhancement effect of the sub(s) can be felt but not heard. The best way to do it is sit in your preferred listening position and have someone turn the sub on and off (or use the remote if applicable) and adjust crossover and level controls until you don’t notice much difference in the bass level when turning it on, but the soundstage collapses somewhat when you turn it off.

I positioned the RELs by ear. Lots of time and moving the subs to find the best spot by trial and error. One trick for finding the best starting location is to place the sub where you sit and move about the room until you hear the sweet spot, then move the sub to where you were standing (or even better, squatting) when you found that sweet spot. If using two, do it again with the second while the first, already optimally placed, is on.

My experience is that it is impossible to place a sub where it will sound its best "throughout the entire room". You can certainly compromise for a good "all-around" placement but it will only perform optimally in one location in your room for a given listening position.

I hope this helps some. Let me know if not.

Dave

Nice to know Tim. Nothing like being set up by someone with an agenda to push posing as a real person with genuine interest in learning. Shoulda known.

I only listen from one position as I am only one person at any given point in time. As for having four subs, I am probably already in the extreme at having two. I am sure there are a few audiophiles that are able to overcome the expense and freedom from real-life constraints (WAF and such) that can or will take advantage of your recommendations. Bet you can count them on your fingers.

You can stop trying to solve the issue for the OP as he went a different direction. One more finger in reserve. Keep counting.

Dave

"One more finger in reserve.."?"

Meaning that the OP went with a different solution, not the middle finder salute. :)

I am sure that you have discovered something of merit, Tim. If anyone will listen, that's another matter. IME, doesn't help to oversell.

Dave

FYI Tim:

http://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer?page=9

Best,
Dave

That thread should keep you busy for a while. ;>)

Best to you Tim,
Dave