Microphone sensitivity specs

[Atreyo Bhattacharjee]

What is the sensitivity of microphones and why is it in negative db?
I understand sensitivity in speakers is the SPL produced when 1 milivolt of power is delivered to the drivers at 1KHz, is this right?

 

[ricdiculus]

Microphone sensitivity is rated in -decibels because it will tell you the quietest sound it can pick up. a mic that can pickup a sound at -20db is more sensitive than a mic that can only pickup sound at -10db. The higher the negative number, the quieter the sound, thus indicating a more sensitive mic.

Speakers are rated by the SoundPressureLevel (SPL) generated by 1 watt of power with a signal that contains the full frequency response the driver is designed for at a distance of 1 meter from the driver in an anochoic (dead silent) chamber. So a sub-woofer would be measured like this: 91db SPL @ 1 watt @ 1 meter, 20hz - 200hz(+/- 3db). A mid-range driver would be measured the same way, but between, say, 400hz - 4Khz frequency range. A full range speaker is typically measured 20hz - 20Khz. All at 1 watt @1 meter. The (+/- x db) part will tell you how well the speaker can produce it's intended frequencies. The lower the number here, the more accurate the speaker is. Some less reputable manufacturers will only test at one specific frequency which on paper, make it appear that there speaker can produce a higher SPL then others, when in reality, it may not even be able to produce the other frequencies in it's range at all (much less +/- 3db).

Whew! Sorry, that got a little long winded. 🙂