I thank Knowles electronics for the support.
- The filter blocks off external materials from getting into the transducer, thus preventing damages to occur deriving from such causes.
- The filter has an unique resistive value, and acts as a passive acoustic filter mainly reducing the first peak resulted by the mechanical resonance at f0.
"The bump at 2 kHz is primarily caused by the mechanical resonance of the receiver: the mass of the diaphragm and springiness, or compliance, of the diaphragm combined wit the compliance of the air inside the receiver." H. Dillon, Hearing Aids, Boomerang Press, Turramurra, Australia, 2001.Their rated performances have been demonstrated by one of the manufacturers, but there has not been a single instance of which an actual IEM has been utilized. So Etymotic Research ER-4B is used to find out how the filters help shape the frequency response of an IEM.
With stock acoustic dampers:
With conventional acoustic dampers:
Since the damper can turn ER-4B into ER-4S with broader frequency bandwidth, maybe vice versa, or even evolving ER-4P into other two might be possible without using an electrical filter. And that will be the topic of my next article, it seems!