Ok, here is all the measurements I found.
Solder Dude measurements of ER2SE, ER2XR and ER4XR with aftermarket ear tips Comply Ts 100 and Spin Fit CP800.
Notice that the first graph, the ER2SE has smaller size font top and botton and it has wider gaps between lines so it looks different at first look but if you carefully compare you will notice how very similiar all these measurements are. The differenced between cheap ER2 and expensive ER4 are tiny, easily nulified by simple EQ and the dynamic driver ER2 has superior high frequency extension.
Impulse response with stock tips, again, very similiar.
THD at low SPL of only 80 dB. Notice how the expensive ER4 has much higher distortion and whats worse, unline most classic dynamic drivers like Sennheiser HD600 where distortion is only problems at low frequencies, the balanced armature driver has peak distortion in mid range around 800Hz, this means the distortion overtone will fall on the most ear sensitive frequency band around 3Khz.
Notice, this is also at very low level, I listen at 87-90 dB peak for compressed music and dynamic less compressed music easily goes above 100db. Now if it has 0.6% THD at 80 dB, imagine what 100 dB peaks from orchestra will do to this poor little driver.
The ER2SE has less than 0.5% peak THD at 94 dB vs ER4XR which has over 0.6% at just 80 dB
ER2SE distortion spectrum at 94 dB, notice most of the distortion is of the less offensive second harmonic even order type, I will mention it later, remember it for now.
SilverEars frequency response measurement of ER2SE and ER4XR, the differences bellow 8KHz are again very small, if this was apples to apples comparsion of ER2SE vs ER4SR they would be almost identical. In highs we can see ER2SE is flatter and more extended.
yuriv Distortion spectrum of older ER4PT model at 94 dB. Please note his microphone sucks and has high distortion so this graph in isolation doesnt mean much.
Here are his other measurements of LG Quadbeats 3, a headphone with super low distortion and Sony MH755, a low distortion headphone too.
The distortion you see here is the distortion of the microphone, thats why these two low distortion headphones look the same. In contrast the high distortion ER4PT reaches far above the distortion floor of this microphone and we can see that most of its distortion is the nasty third harmonic odd order type, think hard clipping of transistors vs soft clipping of vacuum tubes.
yuriv Distortion spectrum of ER2SE, surprisingly it doesnt measure much lower THD as ER4PT but I take this result with grain of salt due to the shit microphone used. Notice, the dynamic driver of ER2SE has mostly second harmonic even order distortion.
Left and right channel distortion spectrum of ER2SE at 94 dB @ 500 Hz by hakuzen. Just to hammer the point of the ER2 having mostly even order distortion.
Crinacle ER2SE vs ER4SR, a apples to apples comparsion. These two are so similiar below 3 KHz that you will find bigger differences between different units of same model of headphone from other manufacturers due to random variability. Above 3 KHz the differences are still small, no night and day difference as some claim, cheaper ER2SE is smoother and more extended.
Crinacle ER2XR vs ER4XR, same as above, just that ER2XR has 6 dB more of sub bass.
Left and right channel distortion of ER4SR from purr1n at SBAF. SPL is little unclear but this should be somewhere around 85 dB at 500Hz. This is better result that the Solder Dudes measurements, third harmonic dominates to 1.6 KHz then its mostly second harmonic.
ClarityFidelity distortion spectrum of ER4SR at 94 dB @ 500 Hz, left and right channel. We can see its mostly third harmonic up to 1.5 KHz after which it changes with second harmonic back and forth on right channel while on left the second harmonic dominates always past the switch point.
Same as above just ER4XR, it has much higher distortion and its mostly concentrated around 800 Hz, same second and third harmonic behaviour as ER4SR.
ClarityFidelity again, this time with older model of dynamic driver Etymotic headphone, the MC5. This one has the Kids max SPL cock blocking filter so little Timmy doesnt obliterate his hair cells while headbanging to Slayer at 110 dB. Notice the much lower distortion compared to the balanced armature ER4SR and XR. There is high distortion peak in left channel at 4 KHz but that can be damaged headphone or measurement error, the distortion is strongly dominated by even order second harmonic.
ER4SR, XR and MC5 waterfall plots. I read reports from subjectivists saying the balanced armature Etymotics have more "speed" than the "slow" dynamic driver, what does "speed" or "fast" even mean? Becose looking at impulse responses and waterfall plots shows that the balanced armature doesnt perform better in the speed that sound decays and if by "speed" is meant literal velocity of the moving membrane, then the dynamic driver is faster as it goes past 19 KHz while the BA drops off the cliff past 16 KHz. Please note the above is the old kids MC5, it has even poorer HF extension that the ER4, it goes to like 15 KHz. I dont have waterfall for ER2SE but I expect it to perform very similiary to the above in terms of decay speed but with extension that goes past 19 KHz as seen in the plots showed earlier.
And best for last, the good old Innerfidelity measurements from times when our lord and saviour, Tyll Hertsens, was still active and Innerfidelity was actually worth visiting.
ER4SR and ER4XR, the midrange distortion is bad in SR but pretty tolerable outside the 8 KHz peak, the XR in comparsion has not only higher midrange distortion peak, but the area under the peak, the lower midrange and bass region is significantly elevated too. Above the peak around the treble they are similiar. If you care about distortion I think at this point its safe to say the SR is strongly superior to the XR.
MC3, a old dynamic driver Etymotic, a predecessor of the modern day ER2, look at the distortion, it completly shits on the much more expensive ER4 series. Also notice how clean the square waves and impulse response are.
TLDR: The balanced armature Etymotic headphones are extremly similiar to the dynamic driver ones in terms of frequency response, decay and bass extension but have higher distortion, especially in the worst place, the mids, and their distortion is the nasty odd harmonic type while the dynamic driver ones have the warm and smooth even order. Also for younger users, the BA Etys turn all music into sort of MP3 due to their high frequency extension which falls into black hole past 16 K. There is not a single measurable advantage of the BA Etys and they cost alot more. The ER2SE and XR are best measuring headphones Etymotic ever made.
