Active noise cancellation degrades the wanted signal and weakens at high frequencies.

Evidence

In the active case, the wanted signal is having noise added to it – not something one really wants to be doing if one can avoid it. If the phase shift is not absolutely correct, complete noise cancelation will not occur, with the result that the wanted signal is then being further contaminated. Furthermore, because of the phase shift requirement, higher frequencies are not attenuated as effectively—something the passive types do very well. — David Howard, Jamie Angus, coustics and Psychoacoustics, 2561

Categorization

• QUESTION: Why exactly do higher frequencies resist antiphase attenuation — wavelength, latency, or transducer limits? Worth chasing in the phase chapters.
• XREF: Ties to the reader’s earlier study of how phase and wavelength interact with transducer response and to phase-matching limits in noise control.