You'll see a lot of specifications when comparing microphones, speaker cabinets, etc., and it can be useful to understand what they may (or may not) mean. If a speaker cabinet is advertised as covering 20-20,000Hz, that's pretty impressive... but the impression is probably misleading. We in the bass world usually care about lows, how low can it go?? The open low E on a bass is about 41Hz, and a low B string sounds around 30Hz, so we may give cabs that start at 60Hz a dirty look.

However, when a mic or speaker shows frequency response specifications, it does not mean that the the device does not pick up or reproduce frequencies beyond the frequency spectrum quoted.

The proper way to express frequency response is not, for a fictional example, 50-14kHz.*, but 50-14kHz +/-3dB. First of all, no device is perfectly flat. Secondly, if you only are given 50-14,000Hz., you only have half the story, you need the +/-3dB** to give you the true picture. When you have both components, it expresses that the device covers 50-14,000Hz with a tolerance of 3dB above or below (louder or softer) the reference response line.
    *when a K is used it stands for 'thousand', so 14K is 14,000. **dB= decibels, a unit of measurement for sound

For example, this is the K&K Sound Golden Bullet Microphone's Frequency Response curve:

You could describe the mic frequency response as 20Hz to 17kHz, but that would be an exaggeration IMHO (shame on K&K). You can see that response begins to drop at 60Hz but is still pretty acceptable down to 40Hz. The upper limit begins to drop at about 12.5kHz and then dives deep around 15kHz.

So basically, when you read the spec, it is actually pretty useless unless a "+/- XdB figure accompanies it.

But in any case, all it is saying is that the response curve drops beyond the specified frequency range, not that it goes away entirely. So, for example, when your typical 10" speaker cabinet's frequency response begins to drop off at 60Hz, you compensate with your preamp or amplifier's controls to beef it up a bit, etc.

For supplementary information, see my FAQ "FREQUENCIES: What are the frequencies of bass notes?".