It is based on this formula: P a v g = 1 T ∫ 0 T v ( t ) ⋅ i ( t ) d t Since the instantaneous power of an AC waveform varies over time, AC power, which includes audio power, is measured as an average over time.
There are no similar loudspeaker power handling regulations in the US the problem is much harder as many loudspeaker systems have very different power handling capacities at different frequencies (e.g., tweeters which handle high frequency signals are physically small and easily damaged, while woofers which handle low frequency signals are larger and more robust).Ī graph of instantaneous power over time for a waveform, with peak power labeled P 0 and average power labeled P avg Mechanical: Loudspeaker components have mechanical limits which can be exceeded by even a very brief power peak an example is the most common sort of loudspeaker driver, which cannot move in or out more than some excursion limit without mechanical damage.High level signals over a prolonged period can cause thermal damage, which may be immediately obvious, or reduce longevity or performance margin. In fact, most is converted to heat, and the temperature must not rise too high. Thermal: Not all energy delivered to a loudspeaker is emitted as sound.Loudspeakers įor loudspeakers, there is also a thermal and a mechanical aspect to maximum power handling. Without regulations, imaginative approaches to advertising power ratings became so common that in 1975 the US Federal Trade Commission intervened in the market and required all amplifier manufacturers to use an engineering measurement (continuous average power) in addition to any other value they might cite. Īs an amplifier's power output strongly influences its price, there is an incentive for manufacturers to exaggerate output power specs to increase sales. This determines the continuous output power. Temperature: The amp's output devices waste some of the electrical energy as heat, and if it is not removed quickly enough, they will rise in temperature to the point of damage.This determines the minimum load resistance that the amp can drive at its maximum voltage. Current: The amp's output devices ( transistors or tubes) have a current limit, above which they are damaged.This determines the peak momentary output power for a given load resistance. Voltage: The amp's power supply voltage limits the maximum amplitude of the waveform it can output.In audio electronics, there are several methods of measuring power output (for such things as amplifiers) and power handling capacity (for such things as loudspeakers).Īmplifier output power is limited by voltage, current, and temperature:
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