# Sensitivity = Efficiency in Speakers?

**Sensitivity** is the output sound pressure level that is measured at 1m when 1 Watt of power is being consumed. The original standard specified 1W, which required converting to volts according to the loudspeaker’s nominal impedance. At 8-ohms, 1 Watt would be with 2.83V applied. At 4 ohms, 1 Watt would require only 2V. The current standard allows using 2.83V into the loudspeaker, regardless of its impedance. This causes some confusion about what is being specified as Sensitivity.

**Efficiency** is the ratio of acoustical output power to electrical input power, measured in watts, expressed as a percentage. The measurement is taken at 1m from the loudspeaker.

If you convert sensitivity to efficiency, assuming an 8-ohm speaker and 2.83V applied, you will find that a loudspeaker with a sensitivity of 92dB is 1% efficient. That’s right, 1%. For each 3dB increase in sensitivity, the efficiency doubles. So 95dB sensitivity is 2% efficiency and so on.

To find the efficiency of a 4-ohm speaker specified using 2.83V input, you simply subtract 3dB from the specified sensitivity and do the conversion. For a 2-ohm speaker, you subtract 6dB. For a 16-ohm speaker you would add 3dB.

Expressed in words, some of the resulting truths sound pretty bad: *For a speaker with a sensitivity of 82dB, one-tenth of one percent of the electrical power applied to the speaker is realized as acoustical power at 1m from the speaker.*

Just to put it all in perspective, one Acoustical Watt is realized at a sound pressure level of 112dB.

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