> More advanced noise-canceling headphones, such as the Bose QC35 IIs and Sony WH-1000XM3s, add feed-forward noise-canceling, which uses a microphone (or two) o

> More advanced noise-canceling headphones, such as the Bose QC35 IIs and Sony WH-1000XM3s, add feed-forward noise-canceling, which uses a microphone (or two) on the outer shell of the headphones to pick up the environmental noise. My oooold Bose QC15s already have microphones on the outer shell - not sure what they are used for, but they are definitely there, with a quite prominent grille...