A clipped amplifier outputs approximately double its rated continuous power, threatening loudspeaker voice coils

When a power amplifier is driven into clipping, the output waveform is flattened at the positive and negative peaks, approaching a square wave. A square wave with the same peak voltage as a sine wave has substantially more RMS (heating) power: the RMS value of a square wave equals its peak value, vs. 0.707 × peak for a sine wave. Driving an amplifier hard into clipping thus delivers approximately twice its rated continuous power to the loudspeaker. High-frequency compression drivers are especially vulnerable: the harmonics generated by clipping fall in their frequency range, and because they are more efficient than woofers, they receive a disproportionate share of the clipped power. This is why a 200W amplifier hard-clipping into a loudspeaker’s tweeter can destroy it even though the spec shows the tweeter handles 200W.

Examples

A 200W amplifier clipping into an 8Ω loudspeaker delivers approximately 400W instantaneous peak power. A compression driver rated for 50W in a biamplified system can be destroyed by the HF harmonics of a clipping low-frequency amplifier if passive crossovers are removed without updating protection.

Assessment

A live engineer clips the amplifier at peaks to ‘squeeze out more volume.’ Explain the two mechanisms by which this endangers the high-frequency drivers.