Just a few comments on various responses here on this most interesting and misunderstood missing link in most peoples audio systems. First I would like to adress a few comments.
1. Most hobbyist use too much bass.
This hobby also happens to be a major form of entertainment for all of us. If "most" like too much bass-ie the "impact" or the "feeling" of live music(more of this in a moment), them what is wrong with that? Yes, overloading the room with more bass obscures the midrange and effects soundstaging. NO arguements, BUT if most do it, there must be something enjoyable about it, and why call it wrong if this is what makes the owners happy. IS this not what these very expensive toys are for?
2. Too much bass is not realistic.
OK, this depends entirely on the music type. BUT, I think most people that are turning the subs up "too loud" are generally not only jazz or classical listeners. These are (with the addition of solo guitar and or bluegrass music)the only live music forms that generally do NOT knock you in the chest with bass when listening as reasonable distances from the array's. Any rock, reggea, country, blues, metal, electronic, pop, and even fusion jazz played live has massive amounts of impact and low frequency energy that is VERY hard to recreate in a home hi fi or ht environment! This generally is very expensive to produce as well. But I am sick of "hi-fiers" saying that live music apparently has no bass. Get out to some "other types" of concerts once in a while! I have heard thousands of hi fi systems, and yes, I work in the industry, BUT I have never heard a hi fi system of any cost that can reproduce the impact and low bass of a live show with 100,000 watts and 300 15" drivers! (Pretty much any amplitheater)
3. The lower you turn the level(or overall gain) of your woofer down, the more bass definition you will hear.
This one is absolutely correct with almost any "under $1500" self powered woofer out there for one reason. They all have limiters in their amps that they are using .These devices- in an effort to save the amp and driver -start cutting the low frequencies entirely-say below 40hz when the amps aproaches clipping point.
If you want low bass at anything above say 100db, it will cost you. If you dont believe this just ask some of the techs in the service areas of some of these speakers manufactures. Almost all affordable subs have these.
OK, I will get off my soapbox and share some experiences that I have learned in room placement.
1. Dont put them in the corner-unless you want +15db at 45-60hz. The closer you get them to the corner the more output and the more hump.
2. Likewise, dont leave it equadistance from the back wall and the side wall-try for a 30% differance in these two distances.
3. Dont put a single woofer in between the mains, this generally is putting the sub directly in a "node area"
4. If you have a self powered woofer that has speaker level inputs and rca ins, use the speaker level inputs. jumper off of the amps outputs with a GOOD set of speaker wire and dont hook up rca's from the pre or at all. This is assuming 2 channel world only, as the better surround pre pro's have very good bass managment that most always improve room acoustics-like notch filters etc....This method of wiring does not effect the load on the amp just FYI...This will help tremendously with the integration with the mains-probably due to phase characteristics...
5.Keep the xover lower than 80hz if using floor speakers that have bass below 50hz. I prefer 55-60 at the top of the range. I read where someone here was taking subs up into the 200hz range. I know that these 10 and 12" speakers have the capability to play these frequencies and higher, look at guitar "heads" (speakers, baffels, and amps all in one box for those who dont know)and they generally have 10 or 12" woofer and no mids nor tweets, but yet are playing the highest notes on a guitar. BUT just because they can doesnt mean that sub woofer designers intended on them to...Generally the amps used in a lot of subs these days are switch mode amps that sound good on bass but horrible elsewhere at there price points. LETS keeps them playing low bass only!
Use two subs if possible for the ultimate. Left and right and as close to the mains as possible to try and time align. I have heard front and rear work well too.
Last, I will just name a few subs that I have heard that I think are truely exceptional for the money. I am a dealer for some and not for others, and I own a Martin Logan Depth, which is FANTASTIC in medium sized rooms. I have mated it with Logan stats, Talons, and now Monitor Audio speakers. This is obvoisly one of my favs. The larger Descent is the same but better in larger rooms.
The Definative "supercube" woofers are quite nice and range from tiny at 9"x9"x9" and $700 to medium sized and "oh my god bass" at $1800! All of these are impressive-
The new Monitor Audio silver 12"/500 watt/sealed is very nice and very musical at $1000.
Another very musical but not very high output in med to large rooms sub is the ERA's 1x10" w/ 500 watt amp-NO Limiters in this ones amp. This one is 1k also.
Lasr, The Velodyne "DD" series subs are the only subs thus far that may get me to sell my Logan.(because of its remote and room calibration) Hmmm...All my favs are servos? Wonder why? :)
Hope this helps get all of your chests pounding and feet moving! After all, is this not about having FUN???