Telephonic handset apparatus having an earpiece monitor and reduced

Abstract

A noise-cancelling handset has reduced inter-user variability. The handset includes an earpiece housing. A space, referred to as the 'front volume' is defined by the rear and side walls of this housing and a front surface containing acoustic ports for radiation of received sound into the user's ear. An error microphone is situated so as to sample the acoustic field within the front volume. In use, a further volume, referred to as the 'forward volume,' is defined between the front surface and the user's outer auditory canal. A leaky acoustic seal typically obtains between the front surface and the user's auditory canal. Thus, the forward volume will effectively have an acoustic leak, which has a characteristic, but variable acoustic impedance that is mostly of inductive character. At least one acoustic port is provided to effectuate a controlled leak to the outside of the handset. The dimensions of the front volume and the controlled leakage port (or ports) are chosen such that the parallel combination of the acoustic impedances of the front volume and the controlled leak is less than the parallel combination of the acoustic impedances of the forward volume and its variable acoustic leak. As a consequence, variability between users (and between incidents of use by the same user) of the loudspeaker-error microphone response is reduced over an appropriate frequency range.