A disposable-type hearing aid uses a relatively large single diaphragm or a large single diaphragm subdivided into a plurality of smaller active diaphragm areas obtained using a grate-like back support plate with ridges which contact and divide the diaphragm into the several smaller active diaphragm...http://www.google.com.hk/patents/US7003127?utm_source=gb-gplus-share專利 US7003127 - Hearing aid with large diaphragm microphone element including a printed circuit board
