Electronics 01
How Do Noise Cancelling Headphones Work? The Timing Math
Noise cancelling headphones play inverted sound, but a 20° phase error leaves a third of the noise. Why ANC kills engine drone and not voices, with plots.
sound
Electronics 02
Why Do Transformers Hum? It's 100 or 120 Hz, Not 50 or 60
Transformer hum comes from magnetostriction: the core stretches about 2 micrometres per metre twice every cycle. Why 100/120 Hz, and what makes it louder.