Three different topologies
The above mentioned ANC principles would work in a very broad frequency range if all conditions were ideal. In practice there are many factors limiting the ANC performance at higher frequencies.
In the ideal world these elements would be total linear within a large dynamic range, have flat frequency and phase response and no internal noise. If this was the case, designing the ANC application would be a piece of cake. Unfortunately we have to face reality: A modern electret or MEMS microphone has quite a high dynamic range, a modest noise figure and a fairly flat frequency and phase response. The same goes for the ANC processor, which “only” adds some time delay as mentioned earlier. But when it comes to the receiver, the picture is a totally different one. Due to size constrains (especially in the in-ear earphones) a quite small receiver has to be chosen (Ø8mm – Ø15mm) and then some performance parameters become quite challenging.