Duty cycle
The power draw and heat dissipation of an amplifier can vary greatly with how hard the amplifier is being driven. One way of describing how hard an amplifier is working is the "duty cycle" of its input signal, which is a way of measuring what percentage of the available power of a system is being used.
In real-world applications, the full power of an amplifier is rarely used because real-world speech and music signals are transient and chaotic, and some amount of headroom is required to mitigate the risk of clipping. The four duty cycles used in our Power Draw / Heat Dissipation Calculator are Idle, 1/8 Power Pink Noise, 1/3 Power Pink Noise, and Full Power.
In general, "Idle" and "1/8 Power Pink Noise" are the only conditions that an amplifier would typically be subjected to in a real-world application.
Idle
1/8 Power Pink Noise
Amplifiers are often tested using pink noise signals to simulate real-world speech and music signals. 1/8 Power Pink Noise is pink noise that is delivered at 1/8 of the amplifier's maximum rated level, or about 9dB below the clipping point of the amplifier. This 1/8 power signal provides a very good approximation of how hard an amplifier would be driven by typical real-world speech/music signals, assuming those signals were being driven as loud as possible without clipping the amplifier.
1/8 Power Pink Noise is the best duty cycle to measure the maximum performance of the amplifier under normal conditions.
1/3 Power Pink Noise
1/3 Power Pink Noise is very similar to 1/8 Power Pink Noise, except that it is a significantly more powerful input signal. 1/3 Power Pink Noise is a pink noise signal that is delivered at 1/3 of the amplifier's maximum rated level, or about 4.8dB below the clipping point of the amplifier. This 1/3 power signal provides an approximation of how hard an amplifier would be driven by typical real-world speech/music signals, assuming those signals were being driven loud enough to clip the amplifier heavily, and produce severe, audible distortion.
1/3 Power Pink Noise is the best duty cycle to measure the performance of the amplifier during heavy clipping, and is not a good approximation of an amplifier being used under normal conditions.
Full Power
Full Power means that the amplifier is being driven with a sine wave at its maximum possible level (i.e. the amplifier is driven to the threshold of clipping 100% of the time). This is generally only used as a torture-test for an amplifier, and no real-world scenario would ever drive an amplifier anywhere near this level.
Full Power is not a reflection of a real-world application. It is an engineering test meant to measure the absolute extremes that an amplifier could ever experience.