Measure of the sound pressure level generated at a distance of one meter from a speaker when the speaker is fed a 2.83 volt signal (1 watt at 8 ohms); efficiency of a speaker creating a certain sound pressure level from a given input with high figures representing a more efficient speaker. Speakers with a high sensitivity are able to play louder with a given input than speakers with a low sensitivity.

In order to increase output by 3 decibels (dB) requires a doubling of amplifier power. Thus a speaker operating at a sensitivity of 88 dB with a 200-watt amplifier would put out the same sound level as a speaker with a sensitivity of 91 dB being driven by a 100-watt amplifier. The higher the sensitivity, the less input is needed to create a given output. Speakers with low sensitivities need large amplifiers to play reasonably loud.

An average speaker sensitivity rating is around 89 to 90 dB. Typically, the most sensitive speakers (and the most efficient) are horn speakers, which may enjoy sensitivities of 95 dB or higher.

Speaker sensitivity is an important consideration when choosing an amplifier. Low-sensitivity speakers need much more power to play loudly while highly sensitive speakers may operate just fine with smaller amplifiers. Of course, larger amplifiers always offer benefits of extended range and plenty of clean power (when well designed), making it a wise decision to purchase high-power amplifiers whenever possible