is a subwoofer for music a good idea??

Depends on the music. Some music (Classical chamber music)leaves the SW completely quiet, while some (organ music) keeps it busy. Pop/Rock benefits from a SW. Most Clasical music does not require a SW, although it is occasionally helpful.

And what frequency range are we talking about? There really isn't much below 30 Hz, so a SW that is good only from 30 Hz up, and perhaps is therefore capable of 200-300 Hz ("fast")may be a good idea. Getting the 100 Hz-and-down out of your main speakers and their amplifier is the greatest benefit.

Although some main speakers may reproduce 40 Hz, this does not always mean that they have a "full" sound in the sub 100Hz range. When you get a SW you may be discouraged that so much of the time that big expensive object it just sitting there like a rock, doing nothing. But it's like the fire department: you don't need it often, but it's nice to have on hand when needed.

Eldartford,
I think that Beethoven's 5th would benefit from sub.
Also having a vinyl playback it's also a large benefit to have a sub especially dealing with warped records.

I use mine on some music..and not on some music. Thats a great benefit IMO.

Dave

I agree with crossing over your sub as low as you can go. I want my main speakers to carry the full musical load and have my sub go where my mains cannot. My last pair of monitors (Revel M20s, just sold awaiting new monitors) were crossed over at 45Hz. Seamless. My new monitors are flat to 30 Hz!! Same size as the Revels. My sub is going to be on holiday most of the time, but when needed it'll be there....peace, warren

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....