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....http://www.google.es/patents/US6163610?utm_source=gb-gplus-sharePatente US6163610 - Telephonic handset apparatus having an earpiece monitor and reduced inter-user variability
Telephonic handset apparatus having an earpiece monitor and reduced inter ...
