- The ratio of the useful power or energy output of a device or system, to its total power or energy input. Also called efficiency (2).
- The proportion of the audio frequency electrical power input to a speaker which is converted into acoustic energy. Power efficiency may be measured, for instance, by driving a speaker with a power input of 1 watt, and measuring its output, in decibels, at a distance of 1 meter. Also called efficiency (3).