HA earphones construction

Giganews Newsgroups
Subject: HA earphones construction
Posted by:  JC (menard…@orange.fr)
Date: Sun, 25 Dec 2011

I would like to know how the HA earphones are built, are they magnetic,
piezo....they are so tiny that I do no understand how they can transmit low
frequencies such as 250 Hz.
I did not found valuable answers with Google, has somebody some info ?