Sound: Quiz – Building Your Band

Unclipped sine wave compared to a sine wave 1dB higher that is clipped

What happens when a signal clips (runs out of headroom, or hits a digital ceiling, or an amplifier runs out of power)? Well, when a sound (such as a sine wave) clips, we start to see a corner that looks like a square wave forming. So what is happening to that sound? We know that the sharp corners on a square wave are high frequencies consisting of odd harmonics – which is exactly what happens.

Spectrogram of 40 Hz sine wave 1 dB into hard clipping

So on the one hand, odd harmonics are not atonal, so as a signal starts to clip, the sound still could be pleasing / musical as it’s still related by integer harmonics – at the very least it’s not inharmonic! But on the other hand, pushing that much power normally found in the low frequencies up into the higher frequencies which need/use less power is a formula for disaster.

THIS is how speakers get blown: when an amplifier runs out of power. As shown above, when (for example) a 40 Hz / low frequency signal meant for the big woofer clips because an underpowered amplifier runs out of power, basically a square wave is formed, converting much of that signal into typical square-wave odd harmonics. These odd harmonics are higher frequency, which get directed at the little tweeter speaker, which then fries.

Contrary to conventional wisdom, too little amplifier blows speakers. You can never have too much amplifier. And now the term “total harmonic distortion” makes a lot more sense!