Why Low Frequencies Win

Noise cancellation works best on low-frequency sounds like airplane engines, train rumble, and air conditioning hum. These sounds have long, predictable wavelengths that are easy to invert accurately.

High-frequency sounds like human speech and clinking dishes are harder to cancel because their short wavelengths change direction unpredictably. This is why noise-cancelling headphones tame the steady drone of an airplane yet barely touch a conversation beside you.