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Friday, August 17, 2012

The effect of acoustic dampers on IEMs

I thank Knowles electronics for the support.
On most of balanced-armature transducer driven IEMs available in the market, there is a tiny screen implemented at the opening of the acoustic output port. This is an acoustic damper, and it serves two purposes:

  1. The filter blocks off external materials from getting into the transducer, thus preventing damages to occur deriving from such causes.
  2. 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:
The first two peaks are definitely being controlled, and especially when the acoustic resistance reaches 2.2k ohm.  After this experiment, I changed the stock green filters (1.5 k ohms) on my ER-4B to orange ones, which are 3.3 k ohms. It's only flatter, with increased high-frequency bandwidth!

And here is the conclusive analysis of the experiment with ER-4, relative level differences plotted all at the same time. Click the graph, and it will get bigger.

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!


  1. ... 필터 구매하고 교체하시느라 번거로우셨을 것 같슴닼ㅋㅋ 한번 빼면 재활용 불가일텐데 orz

    그나저나 언제 한번 알텍랜싱이랑 JBL/하만카든에 OEM으로 제공했던 ER-7(iM616/716, EP720/730)용 필터를 ER-4/HF 용 필터와 비교해봐야 할텐데...
    (ER-7용은 빨간색, 연두색이고 ER-4/HF용은 녹색임다. 색이 좀 다르죠.)

    1. 616/716필터는 빨강이같아보이는데ㅎㅎ

  2. Damn... Impact Felt... It feels so GOOD!!!

    I love this blog!

    Thank you Rin for what you are/have done!


  3. Rin,
    May I ask what kind of luck you had in swapping out the dampers without destroying them.
    I would also like to know where all of the various dampers could be purchased.
    Thanks, Jim
    PS If needed, my email is the same as my PayPal acct.

  4. Found em...

    Perdy Cheap Too.


  5. Hey All,
    While I wait for my damper order. I rolled some greenies into my MC5s.
    Prepare for Impact was RIGHT... They have turned into Bass Monsters.
    Thanks again Rin.

  6. While these dampers may look complicated, they are easy to use and install. Manufacturers offer an installation guide for the specific type and model that you purchase, allowing you to easily use and install the device on your own.

  7. What about interchangeable tuning filters such as the ones that come with the RHA earbuds? How do they work?

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