T
his diagram may make understanding frequency range easier for you, since it also has the piano keys in it. One minor difference though - sometimes in Hi-Fi/aduiophile terms the range may be a bit different, ie, some people may include mids down to around 200hz (and refer to that as low mids, etc) while bass classification may then be "upper bass" from around 80hz to 200hz, and below that is "low/sub bass," etc - since they're usually coming off from the response range of speakers and not just instruments. This is because, for example, most standmounts can only get down to 100hz; some a lot lower, but so as not to confuse with the sub, which has to get cut lower depending on room acoustics, etc, or some reach down far enough that for most music (other than maybe the likes of Lil John and Mahler) you won't need a sub.
As for soundstage (and imaging), this basically comes off the idea that a speaker or headphone system must be able to
recreate, to a reasonable scale, the position of the instruments as they would in a live setting, which is why we use stereophonic recording. For starters, if you share one earbud with another person and you listen to Metallica, you'll hear only one of the guitars, since the usual recording is to put the lead on one side and the rhythm on the other. Even bands with just one guitarist playing live usually records two guitar tracks on some songs, which is why there seems to be more layering to the studio recording vs a live performance and they didn't have a hired session guitarist to play with them. Nightwish for example has some parts of the guitar recorded only on the right, but on the parts where they are heavily distorted and loud, they're recorded a bit like mono with strong signal on both L and R, except it's not stuck on a narrow point in the center of the soundstage like the vocals. I'd assume it's recorded as a
wall of sound, or something like it, with stereo mics, so it stretches across the center.
Also look this one up, I think this is compiled based on the entries on the one posted above :
http://www.head-fi.org/a/glossary-of-terms