A Note on Listening Fatigue

There is something I want to mention, and I am not even sure this is the best way to go about it yet, but indulge me if you will.


This is a cumulative spectral decay (CSD) plot for the Audeze Euclid, generated from ARTA after a typical impulse measurement. The impulse measurement by itself is not very critical or readily understood, and this is even considering a frequency response curve is far beyond what the average user cares about. What I am looking at here is whether the signal decays over time and if there are any ugly resonances or ringing effects. These are typically seen more for over-ear headphones with larger drivers and external speakers by themselves or as part of a room setup. With IEMs, I am looking for a fairly quick decay without much perceived loss in amplitude, but not instantly—audio notes should still get a chance to breathe. The CSD follows the frequency response curve itself. As before, keep in mind the limitations of the IEC711 coupler as it pertains to the higher frequencies. The takeaway is that the Audeze Euclid displays minimal decay and is quite consistent throughout the frequency response.


Here is an example of the same done for another IEM, the FiiO FH5s. This was just what I had available already, having used it in the review of the FiiO BTR5 recently. It is a hybrid IEM in that there is a combination of two driver types, dynamic and balanced armature; with mediocre tuning out of the box, these rely on users to customize to some degree. In addition to the hugely different frequency response, note the appreciable decay around 500 Hz, where I suspect one of the driver cross-overs occur. This combined with that massive energetic mesa from 1.5–5 kHz also results in a fatiguing listening experience to many, including myself.


Another way of representing this data is in the form of decay spectrograms, which makes it easier to visualize the differences once you know what you are looking at. This is derived from a longer sweep response in REW, so the base data is different from before, although qualitatively similar. The Y-axis is the decay time in ms, going either way from the minimal case of zero decay and set to +/- 500 ms for consistency of comparison. The X-axis continues to be the 20 Hz–20 kHz frequency response range, and the heat map is based on the SPL readout from the microphone, wherein red is louder. Since different absolute values have been read out across different IEMs in the past owing to various factors, including volume level, gain, and so forth, the absolute numbers are not critical as it pertains to the story here. I have instead set the range to 40 dB throughout, meaning the heatmap has the same boundary layers to generate the spectrogram. The shape itself will follow the frequency reponse, but remember that this is a top-down view. The key point is that the Audeze Euclid continues to not only display a similar mean signal band most of the way, but keeps actual decay over time mostly symmetrical. Once again, the 10–20 kHz region isn't completely reliable, but also expect similar jumps from most products.


Let's now again compare the Euclid to the FiiO FH5s, which has a more V-shaped curve leading to the SPL drop in the mids as expected. This is not surprising, and we see the change in decay rates around 500 Hz followed by more inconsistency with the aforementioned 1.5–5 kHz rise.


What about another set of IEMs marketed for a flat, neutral, and accurate response? The Etymotic Evo does much better, but there is some harshness around 100 Hz possibly owing to a cross-over from one of the three used balanced armature drivers to another. I did not feel much fatigue here either, with the concentrated peak starting at 2 kHz helping with the neutral response by accounting for the ear cavity resonances. Note that the Etymotic Evo is more dependent than any other IEMs I have tested so far on having a good, deep seal, so that can influence results, too.


At this time, the ThieAudio Monarch is the closest in price to the Audeze Euclid in terms of other IEMs I have here. It is also a tribrid, which makes things even harder to compare, with nine drivers in total per ear bud across three different driver types. Things get rumbly in the sub-bass, but not in a symmetrical manner, either. The prolonged mids are the strong point here, and then the electrostatic tweeters used for the highs are a bit all over the place again. For me at least, listening fatigue has less to do with the driver choice here, but more with cross-over. These are also quite large, so there is a physical factor, too.


On the other end of the spectrum is the least expensive set of IEMs tested to date—the Tripowin TC-01 which will be reviewed separately soon. I'll let the graph speak for itself since there isn't much to say that would be kind to the TC-01.

The Audeze Euclid is physically large, but fits into an average set of ears well, especially with the provided Comply foam tips if foam tips are not an issue for you. This helps account for physical fatigue, or the lack thereof. The tuning with the single planar magnetic drivers is also quite consistent and decay rapid, but not instant. This allows some breathing room for the notes to weigh in before giving way to others, and there are no ringing decays. Even with the rapid roll-off in the highs, It's the least fatiguing set of IEMs I have ever listened to, besting many headphones.