Sound cancellation

[seanspotatobusiness]

This video suggests that sound cancellation is possible with just a microphone, amplifier and surface transducer but doesn't explain how the sound being produced by the speaker/transducer is ensured to be 180° out-of-phase with the sound going through the panels. Is it the spacing between the microphone and the speaker or is something else needed?

 

[davenn]

Is it the spacing between the microphone and the speaker or is something else needed?

he is sampling the sound inside the box then in electronics phase shifting it so that it is 180 deg out of phase then he amplifies that out of phase sound and
injects it back into the box through the speaker you saw sitting on the bottom of the box.

This is an old and quite neat trick
awesome for reducing engine noise in a vehicle and other situations

one simple and easy way is to sample the sound you don't want, use an Op-Amp
in inverting mode, amplify and feed to speaker

 

[kellys_eye]

Getting it exactly 180^o out of phase is desireable but not essential. Desireable because it will 'eliminate' the interfering noise but the idea is 'reduction' which is probably good enough.