MEASUREMENTS: Etymotic ER-4B - "Classic" In-Ear Monitor (IEM) / "Canalphone".

Nice box with accessories. Can't see it well in this picture but in the middle of the box is a small container of "damper"/"filters" and tool to aid in replacement when clogged.

Today, I want to expand the measurements of headphone-type devices to include examination of in-ear monitors. As usual, before posting measurements on a range of devices, I believe it's important to set the ground work as to how it's being done and to what relative "standard". I believe this is useful because when I use subjective descriptions, I think it's always nice to refer to context on the objective side. I have seen numerous reviews use things like star ratings or sometimes seemingly arbitrary "3.5/5"-type scores, but without more concrete, specific examples, often the reader is left without a sense of actually what is being described nor have a "hat to hang on to" when talking about relative differences with another product the reviewer might also be pointing to.

Similar to the AKG K371 back in April 2021 as a discussion of headphone measurements for circumaural (and supraaural) devices, today, I want to focus on one of the first IEM-type (In-Ear Monitor, also called "canalphone") transducers I bought back in the early 2000's. This is the classic noise-isolating Etymotic (often stylized as Etymōtic) ER-4B microPro Earphone. The very first ER-4 came out in 1991 and I believe the 4B version I have is reflective of the intent of that very first design.

While this specific ER-4B model has been discontinued for awhile now since early 2010s, there are still a number of ER-4 series products out there including the ER-4XR ("eXtended Response" meant for "music lovers" who want a bit more bass) and ER-4SR ("Studio Reference" for flatter frequency response). 

As suggested by the variants, Etymōtic makes these earphones for different target uses over the years. This '4B' model was meant for technically accurate "Binaural" monitoring purposes. Etymotic aimed for a flat response that follows a "diffuse field" target (great discussion here on the different targets BTW). 

Here's what their KEMAR manikin-based target curve looks like (dotted line) coming from Etymotic's literature:

And below, another diagram from the Etymotic manual; notice the model variants back in those days - 4P for 'Portable' use, 4S for home 'Stereo' use. Comparatively, notice that the ER-4B on the whole managed the flattest diffuse field targeted frequency response:

The '4B' and '4S' are 100Ω medium impedance headphones, the '4P' is more mobile-friendly at 27Ω. The company also offered a 75Ω resistor adaptor which would convert that 4P to 4S.

Of the 3, the '4B' follows Etymotic's diffuse field target without high frequency roll-off which emulates the supposed room response of speakers. This "flat" target will likely sound brighter than what is typically the preferred sound of something like the ER-4S by most music listeners.

If we scour the Internet, there have been various other reviews / discussions on this line of IEMs - see here, here, and here for more reading. Some measurement for the ER-4S here, and InnerFidelity/Tyll's review of the ER-4SR and ER-4XR here also.

A closer look at mine:

Notice the filter circuitry module along the length of the cable.

Esthetically, these are clearly not the most pretty looking headphones. It's mostly plastic construction. In some of the newer models they use some color to differentiate the right and left channels. On these, all you can make out is that little "L" on one of the ear pieces; I'm tempted to take a small strip of red electrical tape to make the channels more explicit. Notice I've got the triple-flange rubber ear piece in place which fits my ears well and provides a very good seal. The seal is essential when it comes to earphones like these to maintain pressure - especially for bass reproduction.

If you look at the picture at the very top, we see that this comes with 3 sizes of soft rubber pieces plus there's a bag of foam tips that can be used alternatively. I must say that even though the headphones don't look like much, the package with hard plastic case and accessories have that professional air about it.

0. My IEM Target Curve...

As I mentioned last year when talking about headphone measurements in general, we need to be mindful that they are highly dependent on the measurement system itself, and numerous variables each time we capture the data. For example, with IEM's, we have to be mindful of the insertion depth of the earphone, the seal around the ear pieces, and the angle of insertion can easily change results.

As you can see above, the ER-4B has been inserted into the miniDSP (H)EARS for testing. I found that they fit pretty well and when run through the REW measurement sweep, I was able to get some consistent results with insertion depth being the main variable affecting amplitude.

Like with headphone measurements, I took a few weeks to fine-tune the target curve I'm using. The (H)EARS comes with an "IDF" (IEM Diffuse Field) custom calibration curve based on the Etymotic ER-4SR. While the curve will work fine, there were a few things I adjusted after running some IEM measurements and listening based on personal preferences and suggestions I've seen elsewhere:

1. I fine-tuned the EARS' right-left microphone capsule balance a bit. I was noticing some repeatable right/left imbalance results with the stock calibration curve. Not hard to calibrate by just measuring the same earpiece in both ear canals/microphones.

2. Added a +2-3dB bass shelf. This is a personal preference and one I suspect most listeners empirically will prefer. I had a look at the Harman IEM 2017 papers (you can see the curve here) which suggested an even greater bass boost empirically. I personally find the Harman IEM curve too bass-aggressive.

3. Slight adjustment to the "tilt" of the calibration. I compared my ER-4B and the stock ER-4SR-based curves available and removed a +1dB/octave tilt I noticed between 100Hz to 1kHz in the miniDSP target.

No doubt, there is some trial and error plus applying my own subjective preferences to the miniDSP calibration curve. I wanted the result to reflect the stock calibration but felt I had to also reflect what I'm hearing, including the preference for more bass and the subjective brightness when headphones are measured as "flat" using the diffuse field target.

Here's what my final calibration target looked like compared to the original miniDSP (H)EARS file that came with this unit; note that I separated the curves by 6dB for clarity:

So with the target defined, and hopefully reasonably clear, let's get to some measurements!

[An interesting tool you might want to have a look at to see the effect of target curves is Audio Discourse with their database of IEMs along with a host of interactive target curves you can compare them with.]

I. Measurements

Here's the summary "big graph" showing the main measured characteristics for my Etymotic ER-4B:

Most important to sound quality is the frequency response which determines the accuracy of the tonality of what we hear. As expected, given the reputation of these earphones, the response is quite flat. Furthermore, with 3 re-seatings of the earphones doing the best I can to keep the insertion depth about the same, notice that the right-left balance is excellent. Etymotic states that the drivers are matched +/-1dB and indeed this looks to be the case generally with mine. As usual, measurement accuracy deteriorates particularly >10kHz.

Certainly not a bad frequency range for a single balanced armature driver! Since I like a +6dB bass boost which has been embedded in my "flat" target, notice the dip into the lower bass using my target. The tipped up treble frequencies, along with relatively attenuated bass response results in a "bright" sound. 

The waterfall plot looks quite nice. Rapid -40dB range drop-off by 2ms down to 1.5kHz. Below that, into the bass region, the decay is smooth with no ugly resonances.

Electrical impedance is interesting. We're looking at impedance as specified around 100Ω but in the high frequencies, it actually has a 'U'-shaped dip down to ~75Ω by 9kHz. Interesting, and I see that this measurement done back in 2012 showed the same pattern. With only a single driver (BTW: Knowles ED-29689 with tuning circuit), the phase graph is quite flat until that "U" dip.

Using the headphone measurement jig with this IEM in place with sensitivity calibrated, the output is around 88dB/0.1V (notice that since IEMs tend to be quite sensitive, I'll used 0.1V instead of my typical 0.24V with headphones). This works out to 108dB SPL/V sensitivity or 98dB SPL/mW at 100Ω impedance. This is close to the Etymotic specs which states 90dB/0.1V and 100dB/mW; again, I'm sure insertion depth will affect the numbers. I had no problem driving these headphones with my mobile electronics although with better amps like the RME ADI-2 Pro FS R Black Edition and Drop + THX AAA 789, I noticed somewhat better bass (compared to my smartphone or USB-powered headphone amp).

Harmonic distortion was not an audible problem for me but it measures a bit higher than most of the better headphones I've tested. The 3rd harmonic is highest and approaches 1% through much of the audible frequencies at ~95dB SPL level, with a local peak around 800Hz. By 1kHz, THD is down to 0.5%. Note the high distortion below 30-40Hz which can make EQ'ing of those low frequencies challenging so I'd be careful with adding too much gain to the bass in an attempt to overcome the bright tonality.

Noise isolation as shown above is excellent with a good seal. There's some attenuation even down to 100Hz. At 5kHz, the noise isolation is at -40dB using the 3-flange ear tips. Obviously if you're out and about in public, be careful as you could essentially be deaf to traffic noise!

Likewise, with a good seal, sound leakage is minimal:

Even with the signal playing at 100dB SPL, with a microphone just 1" away, we're seeing an average of 42dB SPL from 100Hz-10kHz or just around 20.5dB SPL at 1' (almost exactly the RTINGS finding for the ER4XR). This is as expected simply excellent. Even the guy sitting beside you in the quiet library will have no idea what you're listening to.

Finally, let's look at the 100Hz bandlimited square wave:

Those are pretty good looking, smooth, clean waveforms with very few irregularities at the leading edge. Clearly it's missing low-frequency content when the square wave top slopes down like that.

II. Listening...

I think it's worth taking some time to discuss the sound of these IEMs. I've had them for close to 20 years at this point so have used them for many many hours of listening and there's no issue with "break in" by now ;-). In fact, I can't say I've ever noticed "break in" with tiny balanced armature drivers as opposed to the larger dynamic headphones.

Wearing IEMs of course feels different than circumaural and supraaural headphones. These are the most "intimate" of sonic transducers in that they literally enter the external auditory meatus and block out sound. Indeed this is why Etymotic supplied the replacement filters just in case you get dirt, dust, and earwax plugging up the earphone. Blocking the ear canal increased "autophony" (self-generated sounds like chewing, we might hear our own pulse), and cables which are highly "microphonic" (the rubbing and movement noises of the cables) can be annoying. Hopefully you won't be chewing too much while listening to music but the Etymotic cable is moderately microphonic so that could be annoying to some (I know someone who felt this was a "deal breaker" for him).

The first thing I noticed about these IEMs years ago when I got them was the temporal precision they can offer. To me, this is what "deblurring" of an audio signal sounds like as the headphone portrays the signal with fantastic immediacy. Jim Keltner's "Improvisation" on The Sheffield Track & Drum Record sounds phenomenally "tight" with amazing detail. You'll hear every thump, each percussive attack of the kickdrum, every grain in the shimmer of cymbals. Dynamics are very good with realistic decays that resolve naturally and smoothly over time even if the bass response isn't the most impressive. 

Melody Gardot's relatively new album Sunset In The Blue (DR9, 2020) was nice with the intimate-sounding standard "Moon River". I would say the soundstage is quite wide and deep for headphone listening with well-placed percussion, shaker, occasional subtle cymbal accents, and Gardot's vibrato.

In many albums including Gardot's above, the excellent noise isolation on these allows one to hear deep into the noise floor. In fact it's not difficult to notice hum in the recordings or elevated noise level like on the track "I Fall In Love Too Easily" through much of the song. Like the high relative noise floor of LPs, we can still enjoy the music despite its presence. Certainly this is the type of headphone where one can critically listen to music for flaws.

For some silly fun, check out the recent Yello album Point (DR10, 2020). I have no idea what "Waba Duba" is about, but it sounds cool and is catchy. This is an album where we can also appreciate the limitations of this specific ER-4B model when it comes to enjoying music. The tonality is clearly tipped towards the treble. For example, the high frequency synth sounds on "Arthur Speaks" and "Big Boy's Blues" are clearly overly accentuated, harsh sounding. Likewise, the bass, while present, is lightweight in comparison. Easy to hear the difference as I switch back between this IEM and my modded Dekoni Blue. [BTW, for even more fun with Point, have a listen to the 7.1 multichannel Blu-Ray with Atmos mix!]

For something acoustic, the Ray Brown Trio's Live at the Loa: Summer Wind (DR12, 2003 SACD rip, 1988) sounds fantastic through these IEMs. Wide soundstage, realistic-sounding live presence,  great performances by Gene Harris on piano, love Ray Brown's bass work on "It Don't Mean a Thing". Lots of energy. Listening to the audience applause in live recordings is one way to judge the quality of the sound engineering - the cleanliness of the numerous hand claps - and the subtle background calls and cheers. The realism of these incidental sounds adds to the atmosphere and the joy instilled in the music itself.

My '80s listening pick this week is John Farnham's Whispering Jack (1986, DR13). The tipped-up tonality of these IEMs simply does not work for "bright" old recordings from the early CD years. The remastered version of the classic "You're The Voice" on the 1997 Anthology, Vol. 1: Greatest Hits was clearly superior.

Speaking of the tonality, these ER-4B's were meant for "Binaural" monitoring. Indeed, these are great for binaural-recorded music - Amber Rubarth's Sessions from the 17th Ward (2012) sounded glorious! Voice front-and-center, guitar mid-left, cello left, violin right, drums extreme left on "Hold On" rendered with a nice sense of "air" around the instruments, good 3D impression of depth, with plenty of temporal resolution afforded by the single driver.

Definitely one of the scariest Virtual Barber Shop haircuts I've experienced - freaky bag-over-head, creepy whisper-in-ear - love it! ;-)

III. Summary

This IEM can be disassembled as you can see into its component cable, driver with greenish filter inside, and ear tips. Replacement cables can be bought. There's even a Filter Tuning Kit which I suspect fits this old model as well.

"Precise, clear, bright and bass limited" would be my take-home message regarding the sound of these classic IEMs. While I would not classify them as recommended earphones for "fun" listening sessions, they are light, comfortable, provide fantastic noise isolation and will present the sound in a way that I think is "truthful"; great for studio work for example.

Accounting for my taste in tonality, here's a simple 2-setting EQ that helps push the bass up and tilts the treble down a bit that I find quite pleasurable (at least when not listening to binaural material):

The bass in Yello's "Out Of Sight" (from Point) enjoys a much nicer low-frequency punch now that was missing without the elevated bass. It's actually quite impressive how the little drivers can deliver the lows although make sure not to boost the bass too loud which will introduce significant distortions. High frequencies also will be less "bright" with the EQ and significantly reduces listener fatigue.

And with that, in the days ahead, I might measure other IEMs while using these Etymotics as a point of comparison. In use over almost 20 years that I have owned them, these IEMs have served as a nice "palate cleanser" every once awhile when I've needed to recalibrate my ears.

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Compared to many of the products I've measured and reviewed, it's very clear (obvious) that the transducers - speakers, headphones - are much more difficult to measure than say a typical DAC, or amplifier. No surprise that electromechanical devices are more challenging to quantify than purely electrical products, requiring the consideration of multiple dimensions and tools in order to get a feel of the performance.

In particular, headphones even more so I think are very difficult because they are interfaced to our ears and given all the varieties of head, face, cheek, pinna, and auditory canal shapes and sizes, it's IMO easier to show you WHAT the relative differences between headphones are (results very repeatable with relatively small inter-test variability), than truly HOW it might sound to you. Even in the choice of the headphone/IEM target curve that I discussed above, I've applied a bit of my own subjective preferences; honestly, I hate looking at raw headphone measurement frequency response curves without applying some compensation target. 

When I look around at the various results online, it's clear to see that comparisons are best done relative to the same measurement gear and whatever compensation curve might be used by the tester. Even with "standard" professional gear, I think we have to be careful about how generalizable the results are when it comes to those headphones sitting on our heads and in our ear canals. [Great read showing differences between measurement standards.]

In practice, what this also means is that we should be careful about looking at measurements and applying "recommended" EQ's without recognizing that these are really just rough guidelines. We need to tweak these things for ourselves! Whether it's the miniDSP EARS or something much more expensive like the KEMAR manikin, Brüel & Kjær HATS, or GRAS ear simulator/couplers, these are not skin, flesh, and blood human ears producing the results. My experience with just plugging in EQ settings such as those from Audio Science Review's measurements typically have not resulted in a satisfactory sound without my own substantial tweaking - usually, I have to measure myself with the actual headphones I have in front of me.

Recently, I was chatting with Mitch Barnett (of Accurate Sound) about headphones and creating target compensation filters using binaural canal microphones to actually measure the sound of circumaural and supraaural headphones to compensate for the listener's head-related transfer function. Years ago, we had a discussion on this post and I think one of these days, it'll be fun to try out Impulcifer for this purpose.

If any of you know of another way to measure and create personalized headphone compensation filters, I've love to know! A couple years ago, I bought the Sound Professionals in-ear binaural mics and SP-SPSB-10 power supply box which I still have sealed sitting on my table here; will need to crack them open when I find some time. ;-)

Well friends, it's mid-March - cherry blossoms are out, kids out of school for a couple weeks, days longer and warmer. Spring Break time for the family...

Hope you're enjoying the music!