Etymotic ER4 over the years

Released in 1991, the ER4 was the world’s first noise-isolating high-fidelity in-ear earphone that became the basis of all subsequent in-ear earphones and in-ear monitors worldwide, creating an entire category of consumer electronics. 30 years later, the ER4 is still produced and while it’s changed over the years, it is still channel-balanced to within 1 dB by Etymotic.

If any earphone was to be considered the most significant in earphone history, it would be the ER4, the one that started it all. So I thought it would be interesting to see how it has evolved over the years.

1991 – ER4 (no suffix)

This was the OG. A number of consumers felt they were too bright with recordings that were mixed for playback on loudspeakers. Based on consumer feedback this was split into two different models: ER-4B and ER-4S.

1991 -ER4B (Binaural, 100 ohm)

The original ER-4 was renamed to ER-4B and was meant for use with binaural recordings as with them it was generally not perceived as bright.

1991 -ER4S (Stereo, 100 ohm)

Etymotic reshaped their target curve to adjust for brightness on commercial mixes and the ER4S was tuned to this new target. From an accuracy perspective, technically the ER4B is the most accurate in reproducing the average response of the human ear canal, but the modified curve that the ER4S was based on is what all of Etymotic’s consumer earphones (sans ER4B) conform to.

1992 -ER4L (Low impedance, 18 ohm)

This was a lower impedance version (hence the L) that was never released as ER4L and eventually became the ER4P.

1994 – ER4P (Portable/Power, 27 ohm)

The ER4P had a lower impedance (and thus more sensitivity) to work with the output stages of portable players of that era. There is some internal debate within Etymotic if the P stood for “power” or “portable”. Most people within Etymotic remember it as “power” but outside of Etymotic it is widely assumed to stand for “portable”.

The ER4P and ER4S share the same driver and the difference in frequency response is achieved by reducing the impedance which in turn results in a tilt in the frequency response. So while the 4P was considered a bass-boosted version, it really wasn’t. It just had a tilted frequency response where the bass and lower mid-range tiled up a little bit and the peak and higher frequencies tilted down a little bit. This made it warmer, which many users liked, but it wasn’t as detailed as the ER4S. Since the only difference between them was the impedance, it meant you could convert an ER4P to an ER4S by increasing the impedance (using an impedance adapter or changing the cable to one with the required resistors) and convert the ER4SR to ER4P by decreasing the impedance.

2016 – ER4SR/ER4XR (Studio Reference/eXtended Response, 45 ohm)

Product Review: ETYMOTIC ER4SR Studio Reference and ER4XR Extended Release  In-Ear Earphones

The latest iteration was the first full redesign of the ER4 and is offered in two tunings: The ER4SR (for studio reference) and the ER4XR (for eXtended Response).

The accuracy of the ER4SR to the Etymotic target curve is slightly better than the ER4S and is Etymotic’s current reference model for accuracy. The ER4XR on the other hand loses accuracy because of a bass-boost (to cater to consumer preference for more bass), but unlike the ER4S/ER4P, the bass-boost is not achieved by a difference in impedance (or sensitivity) and is done instead by using a different driver.

This was also the first time Etymotic switched to using MMCX connectors from the 2 pin one they had earlier.

The test of time

Considering it was the first IEM, the ER4 is the oldest IEM still in production, 3 decades later and a testament to how keeping things simple (with its full-range single-BA driver) can withstand the test of time. Over the years, Etymotic has stayed true to it’s idea of technical accuracy while also catering to consumer feedback for more bass. If the last 30 years are anything to go by, the ER4 isn’t going anywhere anytime soon and it’s here to stay, a true classic.


Grateful to Jeb Pasillas and Dave Friesema from Lucid Audio / Etymotic for all their help in ensuring this post is accurate.

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