Active Noise Cancelling and ultra low-frequent singularities!

[Tom]

Hi,

In active noise cancelling systems for head-phones there seems to be
a
focus on ultra low frequent singularities (< a few Hz). Can anyone
tell me how these are related to some physical attributes of the
plant
(speaker,microphone, amp and acoustical path in between transducers)?

Cheers
Tom

[Angelo Campanella]

You will have to formulate the mathematical equivalent of an RC low
pass filter. That filter physically is the capacitance C of the earcup
interior volume up to the ar drum vs the flow resistance R of the earcup
circumaural seal; some are good like jell seals, others are lousy such
as no-seal. Above the rollover frequecy of that low pass filter, decibel
noise cancellation degree is limited only by the gain of the amplifier
and the stability of such gain.

Angelo Campanella