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Monday, August 13, 2012

P2B adapter for Etymotic Research ER-4P

As encouraged by the manufacturer, ER-4P can be easily turned into ER-4S, by simply adding a resistor in series. However, it has been proven quite tricky to turn ER-4P into ER-4B, since ER-4B has a dedicated high-pass filter(100 ohm resistor & 220 nF capacitor in parallel) implemented in its barrel.

Once again, my friend vAsurada, let me borrow his DIY-adapter made for ER-4P, a 3-way switchable passive filter which converts ER-4P into a ER-4S and ER-4B, simply by clicking a switch. He told me (with some doubt) that the accuracy is 99%! And I am pretty sure my regular visitor, Carrot, is the designer of the high-pass filter, but please correct me if I am mistaken.

As seen on the right, the adapter is a dual-layered PCB circuit, with a 3-way rocker switch attached. The switch first bypasses(4P), adds a resistance(4S), and finally adds a high-pass filter(4B) to 4P. The built quality is of top-notch, and I don't think you can get this quality from conventional manufacturers.

And here's the actual measurement of unfiltered ER-4, P&S&B superimposed together at 94 dB SPL @ 1 kHz. The data are very accurate, even by comparing them to the data provided by Mr. Don Wilson, the designer of ER-4. (different insertion depth in consideration)

4P to 4B accuracy is the sole target of interest, since 4P to 4S adapter is simply a resistor in addition. Its accuracy is rather insignificant.

And here is vAsurada's adapter:

Wow, the difference is less than 1 dB within 20~20,000 Hz! If you have this adapter in your possession along with ER-4P, it is same as owning 3 different IEMs at once, only for much lower price. I don't know about the percentage of 99%, but the adapter is damn accurate. I should return the adapter soon, and if you have any interest of purchasing one, ask vAsurada, not me. (no commercialism, please) Last time I asked him, the price was whooping 250 in USD! Anyway, it was a very fun experience, tinkering with this adapter. Thnx, vAsurada!


  1. The schematic, and a comparison chart between P2B adapter and original ER-4B's circuit can be found in the link below(my article).

    I was suprised about the comparison result becuase of how I can easily construct this P2B adapter acurately!

    The work based on the impedance measurement resulf of iM-616 which seems to have identical impedance to ER-4P(See Probably, using ER-4P's impedance data, it can be more precisely builded.

    I uploaded a spreadsheet file that was able to predicts the response of P2B adapter.

    It is very helpful if it is required some tweaks of P2B adapter.

    P.S. I didn't build own P2B adapter, but made a digital equalization filter preset using the spreadsheet. The filter is very simple and great! I'm loving it. :-)

    1. Digital equalization filter presets were uploaded on the website linked below.

      The First file is Electri-Q presets(Electri-Q is an awesome VST EQ made by Christian Budde!, and second one is presets of EasyQ which is great free VST EQ(

    2. Thnx for the reference, Carrot!

    3. Ah! I had a mistake. The impedance data of iM616 wasn't used to design the filter's schematic. It was used only to simulate the change of amplitude response... For designing filter's schematic, I used a patent document of Etymotic, which described informations of ER-4. It includes the schematic of electronic filter used in ER-4B.

      So, there is no chance which make this filter more better. It's already perfect!

    4. Thanks Carrot, I have the ER-4P (and the P-to-S cable), and trying the real ER-4S and the EQed ER-4S, I couldn't really tell the difference.

    5. Carrot, what is the number of the patent that you used? Do you have a link? I've checked a few patent sites and can't seem to find anything. I'd like to be more clear on which models have what circuitry inside them before I make my purchase.


  2. Well over my head...

    Thanks, Jim

    PS Because I am so simple, I'll just buy all three.

  3. Thanks to udauda & Carrot :)

    I have a suspiction about the measurement that seems slightly different insert condition. Nevertheless, it's ok because the difference of ±1dB at both edges of audio frequency can't be recognized by human's dull ears...

    If someone have a intrest to get my PSB adapter, please e-mail me - address is shown my profile. Well.. it's just few stocks because first time I have no idea for sale, so I have very limited meterials for adapter.

  4. Hey Y'all,
    You guys know much more than I do.
    But, I thought that the B Model had a much different frequency response than the P or S.
    Here is a link to what I have seen and was expecting:
    Thanks, Jim

    1. My data are same as Etymotics', just uncompensated, That is all.

      To better understand the issue, here's my data compensated using Etymotic's reference target curve:

    2. Rin,
      I cannot get your link to work.
      I thank you for your work in this field.
      I need much more study.
      Thanks again, Jim

    3. Always many thanks, Jim.

      How about this, copy and past below URL to your web browser.

    4. Thanks Rin,
      I think I am beginning to understand.
      Thank you, Jim

  5. Have you made a difference graph between ER4S and ER4B? If so does it correspond to something like the X-curve?

  6. I went ahead and tried generating a difference graph with the tools I have at my disposal. (There's a small error above 15k):
    Somewhat resembles the Moeller curve:

    1. That is exactly what the designer, Don Wilson of Etymotic Research, intended with 4S & 4P. Approximately, ER-4S is -5 @ 10 kHz, and ER-4P is -10 @ 10 kHz compared to ER-4B.

    2. Found some related curves:

    3. Another tidbit:

  7. I recently bought an headphone amp : C&C BH (model 2).
    This little ampy that could has 2 headphone out ports and port 2 is an "P to B" port, which is quite unique.

    It's only US$ 99,99 on eBay.
    So if you want a portable headphone amp and you have the "P to S" cable you can't go wrong.

    A review.