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