Most people will probably say "20 Hz.", but it is arguably neither necessary nor desirable to have a speaker that is flat all the way down to 20 Hz.
One reason is that most rooms amplify very low frequency signals (the phenomenon is called "room gain"), and having a speaker that starts to run out of gas at, say, 30 Hz., will not matter too much in many cases, as the room can fill the last octave back in to a large extent.
In addition, a speaker that has real 20 Hz. performance is going to be hard to place properly in many (if not most) circumstances, and can wind up giving peaky, uneven bass as a result (that will drive you nuts over time).
Finally, and there are a lot of people who will disagree with this (e.g., subwoofer manufacturers), much of the information on a recording taking place at really low frequencies is, to my ears, amusical junk, like subways going under the studio and mike stand bumps, that I can live without. Then again, if you find that such noises help make the recording sound more "live" or if you are a pipe organ music fan, you'll want deep bass capability in your system.
I would buy a Radio Shack meter* and get a test CD with bass warble tracks (Stereophile Test CD 3, for example) to measure the bass performance with your current speakers. You may already have plenty of low bass.
* Make sure you use the correction chart to correct for the Radio Shack meter calibration errors.
One reason is that most rooms amplify very low frequency signals (the phenomenon is called "room gain"), and having a speaker that starts to run out of gas at, say, 30 Hz., will not matter too much in many cases, as the room can fill the last octave back in to a large extent.
In addition, a speaker that has real 20 Hz. performance is going to be hard to place properly in many (if not most) circumstances, and can wind up giving peaky, uneven bass as a result (that will drive you nuts over time).
Finally, and there are a lot of people who will disagree with this (e.g., subwoofer manufacturers), much of the information on a recording taking place at really low frequencies is, to my ears, amusical junk, like subways going under the studio and mike stand bumps, that I can live without. Then again, if you find that such noises help make the recording sound more "live" or if you are a pipe organ music fan, you'll want deep bass capability in your system.
I would buy a Radio Shack meter* and get a test CD with bass warble tracks (Stereophile Test CD 3, for example) to measure the bass performance with your current speakers. You may already have plenty of low bass.
* Make sure you use the correction chart to correct for the Radio Shack meter calibration errors.