is a subwoofer for music a good idea??

Great post, Sd.
1. Depends upon your monitors' abilities, and of course whether there's any musical programming below their LF performance cutoff.
2. Sufficient? Probably. Will it sound integrated and tight?
Not easy to accomplish.
3. No. Subs are more important for HT special effects. (C'mon, guys, I'm trying to keep it simple here!)
4. Not if it's a good one integrated at a low freq.
Can't stress the importance of knowing what your monitors are doing in your room. Again, oversimplifying, if they're largish 6.5-7" two-ways rather than diminutive 5" there's less need for a sub. If you do try a sub I strongly suggest that you start with FAST ones like the RELs, some Velodynes, and the one I bought, the Boston PV1000 (Vel clone), and start at the lowest crossover frequency, working up until integration is best. And yes, room placement can be key, even more so if it's a cheap, slow sub, which can very easily be worse than no sub at all!
You state that your monitors "go" down to 45-50Hz, but I wonder how many dB they're down in-room? There are some 6.5" two-ways that are surprisingly full-range, but your room-loading has a lot to do with it too. Perhaps you could tell us what your speakers are and room dimensions for more specific advice....

Marakanetz..Ok, I'll haul out the old war horse and keep track of SW activity.

Your comment about warped vinyl really refers to mixing the LF to mono, as when a single SW is used. Actually, if you have two SW, record warp and rumble will drive you crazy. Even though I have several SWI I also have a rumble filter that does the mix-to-mono thing, and it always is necessary when playing LPs.

I do not agree at all that most classical music does not need a subwoofer. A subwoofer transforms classical music (including chamber) in a way that is not apparent unless you've heard the difference. (Transforms all music.)

The separation of instruments is greatly enhanced using a subwoofer. The sound of every instrument is more rounded.

For example...assume a piano, flute, oboe, violin, etc, play the exact same note (same frequency); if all that was being played was that exact note, then you would not be able to tell what instrument was playing it; the sound would be the same. But of course we can tell what instrument played the note. A flute sound nothing like a piano. How can this be? The simple answer is that any note played by a musical instrument involves a much broader frequency spectrum than the particular note being played.

Adding a quality musical subwoofer fills in the bottom of the frequency spectrum of every note played by every instrument. The result is....every instrument sounds more realistic.

1) Yes
2) No
3) Yes
4) No, on the contrary

I did not believe that a sub could improve the overall sound untill I got one, a REL Strata III. All recordings tend to benefit from the addition of a sub, classical and Jazz music actually benefits a lot more compared to Rock and Pop. One of the advantages of a sub is that it will give you the low end resolution at almost half the volume you are used to listening at.

I will not say that REL is the best (have not heard everyone out there) but it certainly should be on the top of your list when you consider a sub.

The biggest problem with subs is that you will never know how good or bad it sounds until you have it in YOUR system and YOUR own room. For smaller rooms, it is generally a good idea to go for a sealed one rather than ported one, to avoid boominess. I have heard similar subs in different systems and they all sound different in different rooms and different systems.

For music the sub needs to be fine-tuned to match seamlessly with the main speakers. In order to avoid the midbass hump the sub needs to be well under the main speakers low frequency roll off and not overlap it.

Just because one has paid for a subwoofer, does not mean it should be in the limelight! Basically, the sub should tell you I AM NOT THERE, it should disappear. SUBTLE is the keyword here!

Depending on your room size, your preference, taste in music, volumes to be achieved, it will take a while before the sub is seamlessly integrated into your system. Many folks expect the sub to start performing at its best the moment it is hooked up to the system and get frustrated, PATIENCE is again a keyword here.

thanks for the great response ,folks!i'm new to this forum buisness,but of all the forums i've visited ,this is the most active.way to go!please keep the opinions coming to help me decide.for those who may be interested , my system is :
cadence arita bookshelves(i would be surprised if anyone in this forum has heard OF them,leave alone heard them! but they are really high quality stuff!)
rotel 971 mk2 integ.amp
rotel 951 cd player
kimber 4PR cables(the cheapest good quality i could find)

additionally,there is a offer on the REL quake,REL Q150E and DEF tech prosub 100TL.any of these any good for music?
all opinions highly appreciated,guys!