frequency range for instrument vs speaker

You can't count on many speakers to make meaningful bass below 50 Hz.

Way too broad a generalization.

I'd say just about *any* loudspeaker would benefit from the right pair of subs properly blended.

Benefit to a bass obsessed audiophile - yes. Required or needed for music reproduction - no.

FWIW, I'll share my experience on this.

I once heard a demo at a local shop. It was a recording of an acoustic guitar. Nothing else. Don't remember exactly what speakers I was listening to. I listened for a while, it sounded very nice. The dealer then said," I'm going to switch things up a bit and let you listen to the same recording, same speakers, same amp. Tell me what you think". I listened again, wow! It sounded more real, deeper soundstage, more immediate, etc. Like the notes were floating out there instead of coming from the speakers. I asked if he switched cd players? "Nope", he said, "I turned on the REL sub in the corner over there".

Even if the notes only go down to 40hz, there's something below that frequency that we feel or sense or something.

There exists an acoustical phenomenon called "undertones". Two frequencies sounding together create a phantom tone well below the fundamental frequency of either of the original tones. Just as with "overtones" (harmonics), the presence of these undertones is a large part of what gives instruments timbral complexity, and what allows one to hear or sense the volume of the space that the instrument or voice is playing in. The sound instruments playing together or alone is a practically infinite matrix of the interactions of fundamental tones and harmonics (under and overtones). If a system cannot reproduce the lowest frequencies, the sound of instruments will definitely be impacted. How much and how important that particular aspect of sound is, is a personal call when we consider how many other things there are that affect correct record/playback.

Ecruz, I wrote my post just after and before reading yours. Your account is a perfect example of what I described.

Clearly a sub often if not usually makes a big difference but the existence of lower frequencies in the harmonics is not required to explain it.

Often when adding a sub, the difference can be the result of the sub being able to better deliver flat response without compression at louder volumes at even the same frequencies that the mains would have to cover otherwise, along the lines that Drew_Exckhardt explains so nicely in detail in his posts.

The chart indicates "low fundamentals" for several instruments. Not sure what that is or how different from the "fundamental". Could it be the same thing as frogman's "undertones"?

There is [url=http://en.wikipedia.org/wiki/Missing_fundamental]This[/url] that I found which seems relevant to the discussion.