Ten years ago I acquired my first in-ear monitor. It was a slightly used Etymotic ER6i I bought at a Colorado Audio Society swap meet. I liked the way the triple-flange “deep-insertion” tips fit so much that they became my regular workout earphones for the next couple of years. Except for having to replace the filters, which clogged regularly every two or three months, the ER6i in-ears were trouble-free. A year after I got the ER6i I began using a pair of Etymotic’s flagship ER4 in-ears as my reference in-ear monitors. They remained in my primary kit for location recording until the Ultimate Ears In-Ear Reference Monitors came along in 2011. Since that time the ER4s have seen less ear-time, not because I don’t enjoy them, but simply because I’ve had so many other earphone options available.
At the 2016 AXPONA show in Chicago I had the chance to see and hear the replacement—or replacements—for the now-venerable Etymotic ER4, called the ER4SR and the ER4XR. These two new in-ear designs look identical to each other except for the SR and XR markings on their barrels; SR stands for Studio Reference and XR for Extended Response. As the latter’s name suggests, the only difference between the two lies in their frequency-response curves. The SR is close to Etymotic’s original response curve for the ER4 while the XR has a subtle and intentional lift to its bass response. Both are priced identically at $349—only slightly more than the original ER4’s $299.
Both the ER4SR and ER4XR come with a detachable five-foot-long cable, five pairs of ear tips (two foam and three triple-flange,) a filter removal tool, additional filters, a ¼" stereo adapter, a cable clip, and a hardshell zippered case. The case is large enough to hold the ER4 and a player, such as the new Astell&Kern AK70. The new ER4 in-ears also come with something that I haven’t seen included with many earphones: a complete set of test results for each ER4 capsule. One last detail that isn’t common for under-$350 in-ears—each capsule has its own unique serial number.
The ER4SR and XR both use the same driver technology that employs a single full-range balanced-armature driver. Etymotic declined to name the company who built the driver, but did admit that it was OEM’d for them by a firm that specializes in the manufacture of balanced-amature drivers. Using a single full-range driver eliminates crossover and phase issues at the crossover point because there is no crossover! But according to many earphone designers, making a single full-range balanced-armature driver with even response throughout its entire frequency range is nearly impossible. Etymotic eliminates the most egregious frequency anomalies by creating a tuned enclosure with a specific volume, shape, and composition to minimize the peaks and bumps in its frequency curve. Even the replaceable filter at the front of the ER4’s barrel is designed to do double duty: to protect the ER4’s innards from moisture and debris, and to serve as a high-frequency smoothing filter.
The Etymotic ER4SR’s characteristic curve was first developed through in-house proprietary testing done in the late 1970s and further refined in 1987. According to Etymotic, because the ER4 was designed for a deep-insertion fit that eliminated many of the characteristic colorations imposed by the beginning of the ear canal, the ER4SR and XR have an intentional boost at 2.7kHz and 5kHz, which simulates and recreates the boost that your ear (due to its shape) normally supplies to all aural stimuli. Because the ER4’s deep-insertion fit bypasses this part of your ear these colorations must be reintroduced.
Every in-ear monitor I’ve reviewed has had a particular “house” frequency curve that each manufacturer claims is a result of its own in-house, proprietary, and rigorous testing. One might assume that if the testing gear were set up identically all manufacturers would have the same curve, but that is certainly not the case. Sonic differences most likely stem from the fact that the manufacturers do not all use identical test methods or equipment, and often these exact test methods are carefully guarded secrets. During a headphones panel discussion at an audio show an audience member asked, “Why can’t manufacturers come up with an absolute standard (and accurate) frequency curve for all earphones?” Several manufacturer representatives explained that each company feels that its own methodology is the best one and none felt any urge to collaborate with their competitors for a new standard. This is why earphones from various manufacturers sound different—because they are intentionally “voiced” based on what each manufacturer’s R&D team feels is right, not any universally-recognized, codified standard.
Included with every ER4 Etymotic is a sheet with the test results—originating from a G.R.A.S. RA0045 ear simulator—for that particular pair of earphones. Test info includes each unit’s actual sensitivity and its total harmonic distortion in addition to individual channel levels. My own mono sinewave sweep tests showed me that the vast majority of these minor channel imbalances were inaudible. The ER4SR had the best channel balance, but the ER4XR had the least amount of total harmonic distortion, with one driver producing an astonishingly low .15% while one of the SR drivers had the highest THD at .81%.