One big subwoofer or two weaker subwoofers?

I agree with Rives, depends on a lot of other things. There is no "one size fits all" answer. His link along with other usefull info. should help you decide on which may work best for your system and room.

This thread has some great info. on bass and speaker design along with what can happen as you try to blend the wrong sub with your speakers. While the thread is not about subwoofers..the principals apply for a smooth blend. http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1032037028&openfrom&61&4

Fast bass Slow bass is another good read...http://www.soundstage.com/maxdb/maxdb061999.htm

You may also want to do some reading at this AA forum, http://www.audioasylum.com/forums/rives/bbs.html

Dave

"Faster". What does this mean? Here is what I think.

Frequency response is part of the story. A subwoofer that is flat to 400 Hz will handle 80 Hz better than one that is flat to 200 Hz.

However, a loudspeaker that reproduces the LF waveform perfectly can still be "slow" in the sense that the amplitude of the sound builds up slowly, and perhaps persists after the electrical signal is cut off. This characteristic does depend partly on the size of the driver, with large ones tending to be slower. However, apart from the enclosure, the full story involves not only the size of the driver (actually the moving mass of the cone) but also the strength of the motor that drives the cone: the voice coil, magnet, and amplifier. My 15inch drivers, for example, have 4 inch voice coils, massive magnets, and are driven by powerful amps. They are not slow. The characteristic of a driver that would correlate with slowness is a ratio of motor force/volt to the moving mass.

Also, I must mention my view that most very low frequency sound sources are, by nature, slow. A large organ pipe, for example, does not sound forth at full volume when activated, and it continues to emit sound after it is turned off, not to mention the hall resonance that can be strong for several seconds. I think that what many people take to be "slowness" in subwoofers is really the nature of the sounds they reproduce.

Finally, aren't subwoofers fun! How often do you see similar debates about tweeters?

Ive used the same single subwoofer for over 20 years. It is a 17 inch Altec Lansing Driver. I am unsure of the model but was designed for large venue sound. I built the vented enclosure (3/4" ply oak veneir) exactly as called for by the tested driver's specifications (optimum curve).
It is powered by a mono bridged hafler 220 (450 watts)via monster cable. I use a crown fx2 crossover set @ 80 Hz. The stereo speakers are smallish Energy's powered by a Crown 300A.

Clearly there are many variables in all this but over the years my experience with this system has been nothing but intense pleasure. It can rock with the best of them and yet is smooth and delicate when required. Certainly over 2 decades my music tastes have varied but remain partial to the blues.

The only downside is the size of the enclosure; about 3' X 3' X 16". And I must admit to a few late night visits from the local constabulary but Ill blame that on the beer, good tunes and friends.

Good luck

Thank you very much for all responses.

The main speakers are Kef Q5. They are not very good speakers, but I wish I could exchange it. If so, I would like to use high quality monitors, or maybe electrostatic panels.

The sub-bass system would help anyway. And it is quite cheaper to build a system this way than buy (reallly) full rang speakers, which are out of my budget (now, and probably always).

Now I use a Kenwood subwoofer. It is slow in the sense that it can not follow the rhythm of the music. It sounds delayed. And of course it can not produce musical notes. Just boom-boom.

My system is 7.1 Kef Q series home theater, but it is mainly used for music DVDs. While my actual boom-boom subwoofer is fine for films, it is not right for music. Therefore I can expand the bass of my main speakers.

I know that neither my actual main speakers (which are said to go down up to 40Hz, but I am sure that it is not true), nor any future speakers will sound very deep, so I am afraid that a bit of low-midrange frequencies should be present from the subwoofers always.

Thanks again. I am going to begin a new thread just to know the differences you feel (not only the specs) when listening to different Rels.

Thanks a lot once again.

Mavilla: Try filling the interior volume of the sub with a varied density of foam ( or polyester fiberfil as a second choice ) and turning the crossover point as low or almost as low as it will go. This should get you a lot closer to something musical rather than something that goes "boom boom". You can fine-tune the quantity i.e. how "tight" or "loose" you want the bass by varying the amount of stuffing in the box. This shouldn't cost you more than about $10 or so to try and will probably make you a whole lot happier. Don't forget to try various placements for the sub once you get things dialed in reasonably close to where you want them with the stuffing.

El: As far as motor structure and mass goes, my Brother's 5" mids and 9" woofers both have 3" voice coils. The 9's have less than 30 grams of moving mass. How's that for "transient response capability"? From what i can tell, this is equivalent to having a fully massaged "big block" bolted into a shopping cart : )

Even with this much "motor structure" and lack of reciprocating weight, these drivers don't demonstrate the high "force factor" aka "slam" that many larger and heavier drivers are capable of. The bass is very tight and punchy, but it just doesn't have the "weight" or "impact" that one can achieve by using a larger driver. Even though my Brother is using two 9" woofers per side, he knows that he's missing bottom end. That's why he's also running two larger sub-woofers per side : ) Sean
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PS... Many folks confuse large quantities of bass and / or bass over-hang with deep bass extension. Since it is easier to obtain greater output at higher frequencies than it is to go deep and maintain high levels of linearity, many manufacturers substitute "bloom" for bottom end. Once one gets rid of the "artificial boost", you can really hear the lack of extension. I am going through this right now with my Father and his system. After rebuilding / modifying his system, he thinks he's missing deep bass. Since we effectively made his cabinets larger, which extends bass response, there is NO way that this is possible. What he's doing is confusing the lack of upper bass "bloat" for deep bass extension. While he's VERY happy with the improvements in bass definition and tonality, the lack of 80 Hz bass makes him think that the system is "lean". That's why i'm working on a 15" sub-woofer for him now : )