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Topic: Harmonic distortion in headphones (Read 2526 times) previous topic - next topic
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Harmonic distortion in headphones

I recently asked myself, when trying some new dynamic drivers IEMs and comparing them to by favorite BA-driven Audéo PFE, why I keep prefering the latter. They just have an unsurpassable upper midrage-presence for me, even though the IEMs I tried seem to have an almost exactly identical frequency response. After taking another look at the measurement graphs provided by InnerFidelity, however, I noticed that BA-driven IEMs like the Audéo or the almost identically sounding Etymotic ER4S have one discerning property: compared to dynamic drivers, they have very high levels on harmonic distortion, particularly around 1 kHz where distortion levels go well above 1% (PFE, Etymotic) and our hearing is most sensitive (someone on Head-Fi actually ABX'd the distortion levels of the Etys against dynamic driver headphones).

Well, it could just be the case that I have becomed accustomed to those harmonic distortions and actually prefer them over a more transparent performance, like people prefering tube amps - but usually I strongly prefer transparency. Now we all subconsciously compare headphone sound to listening to a good stereo system and most records are produced to sound best on such a system. It is virtually impossible to reach distortion levels of good dynamic driver headphones with speakers and room effects (see the bottom of this page for a distortion graph of a room system, the levels are very significant). Thus, it occured to me: could it be possible that a "decent" (e.g. subtly audible) level of distortion on IEMs may actually give them a more "realistic" sound closer to what we expect from a good listening room?

Btw. I never "missed" harmonic distortions on my Sennheiser headphones. Could that be explained by their open design allowing some room ambience the IEMs are lacking?

Re: Harmonic distortion in headphones

Reply #1 –
Quote
Well, it could just be the case that I have becomed accustomed to those harmonic distortions and actually prefer them over a more transparent performance, like people prefering tube amps - but usually I strongly prefer transparency.
It could be...  Harmonics are "musical".    But if you can't identify what it is about the sound that you like, nobody else can either.    

It may be that there is more frequency-response difference in your ears than in the measurements (due to the way they fit, etc.).  Or, maybe you like the louder one?

Quote
(someone on Head-Fi actually ABX'd the distortion levels of the Etys against dynamic driver headphones).
It would be impossible to do a proper blind test.    Anybody could ABX in-ears against headphones.  ;)  

Re: Harmonic distortion in headphones

Reply #2 –
The measurements you linked show a 5 dB difference in the sensitive lower kHz range. I'd call that significant.
Distortion is very similar at 100 dB SPL and not that different at 90 dB SPL.
"I hear it when I see it."

Re: Harmonic distortion in headphones

Reply #3 –
Quote from: DVDdoug on
It may be that there is more frequency-response difference in your ears than in the measurements (due to the way they fit, etc.).  Or, maybe you like the louder one?
It could certainly be a subtle feature of the frequency response, but the Etys, as xnor noted, have a similar but not quite identical response and the same midrange quality to them, that none of the dynamic driver IEMs I have tested so far - some of them also measuring very similar - seems to produce for me. And no, it's certainly not the loudness. Of course I'm subject to subconscious bias but I'm not naive - besides the SPL of both the PFE and Etymotic is below that of most dynamic driver IEMs.

Quote
(someone on Head-Fi actually ABX'd the distortion levels of the Etys against dynamic driver headphones).
It would be impossible to do a proper blind test.    Anybody could ABX in-ears against headphones.  ;) 
Duh. ABX'ing headphones against each other is such a ridiculous idea that I didn't thought anyone could interpret it that way. You should have read the post I linked to. Note that - of course - I didn't say he ABX'd both IEMs against each other, but only their distortion levels - by ABX'ing synthetic samples with increasing levels of added harmonic distortion and noticing that on dynamic driver IEMs he can detect much lower levels of distortion than on the BA-driven Etys and that subjectively the clean signal on the Etys sounded like the dynamic driver IEMs with some level of added distortion. I guess I have to take that test for myself...

Quote from: xnor on
The measurements you linked show a 5 dB difference in the sensitive lower kHz range. I'd call that significant.
Distortion is very similar at 100 dB SPL and not that different at 90 dB SPL.
Well, I'm affraid you got me completely wrong. They sound actually pretty much the same to me, and share that upper midrange quality I don't experience when listening to dynamic driver IEMs. I linked to the PDFs because they show the THD levels for both IEMs, which are very similar because of the inherent limitations of their balanced armature drivers.

Anyway, isn't it an interesting hypothesis to ponder whether a low level of harmonic distortions, just at the threshold of audibility and similar to the harmonic distortions produced by very good speakers in a listening room, may actually benefit the perceived quality of headphones/IEMs, by giving them a more "roomlike" sound?

After all, we go to great lengths to perceptually approximate a listening room with headphones by tuning them to a modified diffuse field HRTF with added room corrections for treble and bass response and possibly even by feeding the signal through a crossfeed and adding reverb. Why should that stop with harmonic distortions?

Re: Harmonic distortion in headphones

Reply #4 –
I don't understand. You wrote:

Quote from: Northpack on
Audéo PFE [...] They just have an unsurpassable upper midrage-presence for me, even though the IEMs I tried seem to have an almost exactly identical frequency response.


And I wrote that the 5 dB difference is significant. If you listened to sweeps and compared the two, then they might sound very similar, but we're talking about music reproduction here, right?
Keep in mind that this +5 dB will not only boost lower treble, but also all the harmonics of tones in the midrange.


Anyway, what you are saying is that compared to other dynamic in-ears, with even more significantly different FR, you hear differences in the quality of the midrange and your hypothesis is that this is due to higher distortion in the lower kHz range?

You could test that, but first you'd need to equalize the significant differences in FR.
What would be interesting as well, possibly even more so, was testing intermodulation distortion.
"I hear it when I see it."

Re: Harmonic distortion in headphones

Reply #5 –
I don't "feel" causality in this.  it's not like THD+N values are telling much about the type of distortions.  it's really too much of a stretch to compare speaker+room distos with BA driver distos in an IEM IMO.
deciding that the reason to prefer one type of driver is the extra distortions, seems really hard to confirm objectively. you'd need to turn the "almost exactly identical frequency response" into really almost exactly identical FR and matched loudness to remove at least those 2 variables below audible levels and start listening at the rest. and that does involve measuring your own pair. just looking at the measurements of the same model on innerfidelity isn't reliable enough to conclude no audible FR difference(sadly).