Sensitivity

Sensitivity of what?

-RW-

Definition:

Speaker sensitivity is a measurement of the amount of sound output derived from a speaker with one watt of power input from an amplifier. Sensitivity is usually measured with a microphone connected to a sound level meter placed one meter in front of the speaker. Speaker sensitivity is used to determine the amount of power necessary to drive or operate a speaker.

Very often incorrectly referred to as speaker efficiency

Usually, sensitivity is specified for a specific voltage from the amp, usually 2.83V RMS or 1W into 8 Ohm. The higher the sensitivity, the higher the SPL from the speaker for a specific amplifier output voltage. All else being equal, a 4 Ohm version of the speaker would have 3dB more sensitivity than the 8 Ohm speaker because for the same amplifier output, you putting double the power into the 4 Ohm speaker.

Sensitivity comes at the expense of enclosure size if you want to maintain a certain bass response. Higher sensitivity means bigger speakers. You need about 6 cubic feet for a vented enclosure for a woofer to reach 40Hz and maintain 94dB sensitivity. You only need .5 cubic feet for a smaller woofer to hit 40Hz, but you then only have 84dB sensitivity. You'd need to pump 10W into the 84dB/8Ohm speaker for every watt you pump into the 94dB speaker to hit 94dB.