Sensitivity
Definition
Sensitivity is how loud a speaker plays from a fixed input. The standard rating is sound pressure level (SPL) in decibels at 1 meter with 1 watt of input, written as dB SPL / 1W / 1m. A speaker rated 90 dB produces 90 dB at that distance from 1W.
Higher sensitivity means more volume per watt. Lower sensitivity means you need more amplifier power to reach the same loudness.
Formula
Every 3 dB change in sensitivity halves or doubles the power needed for the same SPL:
- 90 dB vs 87 dB: the 87 dB speaker needs about twice the power
- 90 dB vs 84 dB: the 84 dB speaker needs about four times the power
Some manufacturers rate sensitivity at 2.83 V instead of 1W. At 8 ohms, 2.83 V equals 1W. At 4 ohms, 2.83 V equals 2W, which can make a 4 ohm speaker look more sensitive than a 1W/1m rating would show.
In a stereo system
Use sensitivity with room size when choosing amplifier wattage. An 88 dB speaker in a medium room often wants 75 to 150W. An 84 dB speaker in the same room may want 150 to 300W. Build HiFi uses manufacturer recommended power ranges for pairing scores. Sensitivity still explains why those ranges differ.
