Over the last
decade, the headphone market has seen a boom in sales and growth. This
expansion in business has caused a lot money to be poured into research into
headphone development for a better understanding of listener preferences. Much
of the new research into headphone technology has led to some surprising
conclusions, including one paper recently published by Jeroen Breebaart in the
June 2017 issue of The Journal of the Acoustical Society of America. The
findings of this paper can be mostly gleaned from its title: “No Correlation Between
Headphone Frequency Response and Price
.”

The research
for that study measured the frequency response of 283 headphones over a wide
range of pricing from $4 to over $5000 and found that the frequency response
had a nearly insignificant correlation to the cost. In other words, just
because you spend more money, doesn’t mean you will get a pair of  headphones with more linear or better
frequency response characteristics. In-ear, supra-aural, and circumaural
headphones were the headphone types that were examined, and the study also
showed that there wasn’t even much of a correlation of frequency response to
headphone type.

One of the
reasons why this is surprising is because frequency response was found to be
the major determinant of sound quality in headphones, based on previous
research by Sean Olive and Todd Welti. Some might wonder if other attributes of
sound reproduction play an equally important role as frequency response, but
this does not appear to be the case. Nonlinear distortion like harmonic
distortion can crop up when a headphone is driven hard enough, but most
headphones seem to have enough headroom for that not to be an issue. We asked Dr.
Sean Olive about how much nonlinear distortions would be a factor that could
separate the sound quality of different headphones.

He replied, “Based
on our research and others, I believe frequency response is the dominant factor
that determines sound quality. We’ve done some experiments where we equalized
the headphones to have the same frequency response so that listeners could
focus on distortion differences. The headphones sounded sufficiently the same
that listeners could not say they preferred one to the other except in 1 or 2
cases where the distortion was really high.”
Time-related properties such as
group-delay would also seem not to be an issue in headphones, since most
headphones are minimum phase up to high-frequencies where it is not audible, and
any changes in the phase response would necessarily cause a change in the
frequency response.

What Olive and
Welti found was headphones that were perceived 
to have the most neutral frequency response were preferred by trained
listeners. In other words, much like research conducted for loudspeakers,
listeners gravitated toward accuracy. In view of Breebaart’s finding’s, this
then begs the question of what is the sound quality advantage of purchasing
expensive headphones?

Headphone Measurements

Digging a bit
deeper into Breebaart’s paper, there were some minor differences in price and
headphone type. For example, the more expensive headphones did not seem to have
quite as much variance in low-frequency response. This might be due to manufacturers targeting a more neutral response, but it may also be due to the more expensive headphone having a better seal around the test ears and therefore a more consistent bass response. Also, in-ear headphones had a
greater levels of low-frequencies, although that might be due more to testing
conditions than what would be experienced in normal listening conditions. A
dummy head was used for all testing that might have had a greater acoustic seal
than normal human in-ear use.

One interesting
aspect that Breebaart uncovered was how closely the average response of all the
headphones followed that of an accurate loudspeaker’s in-room response, the
‘neutral’ response. According to the research of Sean Olive, Todd Welti, and
Elisabeth McMullin, the response of an accurate loudspeaker in-room was found
to be very close to the preferred response by listeners. However, when the
average of all measured headphones in Breebaart’s survey was compared to the
target response curve devised by Olive, Welti, and McMullin, the average did
have more energy in the 50 Hz to 2 kHz region than the target curve. The
average curve also had substantially less deep bass below 30 Hz than the target
curve. It should be stressed here that the averaged curve deals with a lot of
different headphones, and their response varied greatly. You can’t pick a set
of headphones at random and expect its response to resemble the averaged
response curve from this measurement set.

Another feature
that emerged from Breebaart’s study is that the average response of circumaural
and in-ear headphones more closely matched the ‘accurate loudspeaker in-room’
target curve than the average response of the supra-aural headphones.

The greater
meaning of Breebaart’s study, and building upon Olive and Welti’s research, is
that the price of a set of headphones is not a very significant indicator of
its sound quality, assuming that the deviation from a ‘neutral’ response is a valid descriptor for the perceived quality. While it is true, as mentioned before, that the more
expensive headphones exhibited somewhat less variance in their responses than
the inexpensive headphones, the difference between the two was not tremendous.
And, as the author states among his conclusions, “there are plenty of relatively cheap models that match
the assumed target function, as well as very expensive ones that deviate
significantly from an assumed ideal response.”

Furthermore, a capable enough headphone can reasonably
simulate the qualitative sound of any other headphone with equalization. Olive,
Welti, and McMullin did just this in their study “A
Virtual Headphone Listening Test Methodology
” where they used
a plethora of filters to make their Sennheiser HD 518 headphones sound like
other headphone models. In light of this, it looks to be possible to have a
inexpensive headphone mimic the sound quality of an expensive headphone, so
long as the frequency band range and dynamic range are available. In fact, this
is the goal of the TB Morphit, a VST plug-in that can
shape the sound character of a wide variety of headphones to imitate that of
another model, or aim for another response such as more neutral responses. One
of the reasons for Breebaart’s study is to determine if there was a case for TB
Morphit, ie. software that could use one pair of headphones to emulate others,
or, as Jeroen told me, “One of the main reasons for looking into headphone
frequency responses was actually to see if there would be a case for headphone
correction tools, and whether there is a specific price category for which that
would be useful.”

Morphit

Reportedly TB Morphit works very well in recreating the
sound of one headphone in another headphone. There might be some small
differences, however, such as manufacturing differences in the measured model
or user’s headphones. Also, if the headphone was seated differently on the
test dummy’s head than the user’s head, that could cause a slight difference.
Aside from these differences, which are not likely to be severe, TB Morphit
should recreate the sound character of any headset on any other headset in its
list of headphone profiles. From a sound quality perspective, with TB Morphit,
once you have purchased any headphone of their list, you can then listen to any
other headphone on that list of profiles. Buying one headset with TB Morphit
allows you to experience the sound of all 143 other headphones profiled, along
with a handful of generic profiles including the ‘neutral’ curve. More
headphone profiles are expected to be added in the future.

Why Buy Expensive Headphones?

Confronted with this fact, the only reason to seemingly
purchase a high-priced headphone is comfort, build quality, or luxury
amenities. It would appear that its ‘sound’ is being removed from the equation,
since it can easily be replicated by a less expensive headphone. The question
then is what impact will this research have on headphone consumers? What impact
will it have on headphone manufacturers? How will this line of research change
the headphone market when quality is merely a matter of frequency response, and
frequency response is so malleable that the sound of one headphone can
effectively be transformed into another? We are hoping to see this research
acknowledged industry wide and is used to push the state of the art forward.

Joe B posts on July 14, 2017 16:53

GrizzledGeezer, post: 1198066, member: 83055
Off my head would be more accurate, I think.

Thank you for the implied agreement as to the superior sound quality of electrostatic and planar-magnetic headphones.

From my subjective perspective, it is not implied, but a reality.

GrizzledGeezer posts on July 14, 2017 16:40

Joe B, post: 1198061, member: 80232
Please, not in the trash! I’d be glad to take them off your hands. I have a spot right next to my Oppo PM-2‘s where they can live.

Off my head would be more accurate, I think.

Thank you for the implied agreement as to the superior sound quality of electrostatic and planar-magnetic headphones.

Joe B posts on July 14, 2017 16:23

GrizzledGeezer, post: 1198060, member: 83055
Sean Olive has long been spreading the erroneous belief that frequency response is the only thing that matters – that (other than distortion) it is the sole determining factor in the accuracy of any product. I guess that means I should toss my STAX electrostatic headphones in the trash.

By the way, STAX made an equalizer (the ED-1) which corrects for the frequency response difference between “free field” and “diffuse field” sound. I have the ED-1, and you can indeed hear the difference (which I judge to be an improvement). But the article says nothing about this.

The following (admittedly hyperbolic) piece discusses the ED-1.

http://rinchoi.blogspot.com/2014/02/stax-ed-1-monitor-legacy-from-past.html

Please, not in the trash! I’d be glad to take them off your hands. I have a spot right next to my Oppo PM-2’s where they can live.

GrizzledGeezer posts on July 14, 2017 16:17

Sean Olive has long been spreading the erroneous belief that frequency response is the only thing that matters – that (other than distortion) it is the sole determining factor in the accuracy of any product. I guess that means I should toss my STAX electrostatic headphones in the trash.

By the way, STAX made an equalizer (the ED-1) which corrects for the frequency response difference between “free field” and “diffuse field” sound. I have the ED-1, and you can indeed hear the difference (which I judge to be an improvement). But the article says nothing about this.

The following (admittedly hyperbolic) piece discusses the ED-1.

http://rinchoi.blogspot.com/2014/02/stax-ed-1-monitor-legacy-from-past.html

posts on July 11, 2017 19:01

shadyJ, post: 1197411, member: 20472
According to the frequency response graph, the HD800S will have more upper treble and deeper bass. It has a wider frequency response band.

One thing that can affect bass response is the seal of the headphones around the ears, so if the HD800S has a better fit on your head, that can also contribute to the bass response.

A tight seal can definitely boost the bass especially in a closed design. Believe me I know, I have the Audio Technica ATH-M50. Actually, along with the M50’s I also had the Massdrop AKG 7XX on hand which I believe are the AKG Anniversary headphones so I listened to all 4 headphones back to back. But for the sake of this discussion it makes more sense to keep it to the HD600 & HD800S.

The difference between the 600 & 800S is more than just lows or highs but the much more articulate lows, mids and highs that they reproduce. It’s the overall transparency and resolution that they provide. Like they say, they remove the glass pane. I hate to use the term “air” because I know many around here don’t like it but that’s the best way I can describe it. As soon as I listened to them I realized that they provide what I seek out and prefer when looking for speakers.

Interestingly, the HD800S sounded the most similar to how my 805D’s sound in my home, go figure (I know some hate how they measure). At first listen of the HD800S I remember nodding my head and thinking “That’s what I’m talking about!” To my ears, a stunning top notch headphone.

I worry that inexperienced listeners/enthusiasts will look at thread titles like this and think that if measurements of speakers or headphones are close or within a target band that one transducer will sound similar or just as good as the other. Why bother to listen, you won’t hear a much of a difference- it says so right here on paper. I see that kind of thinking all the time. A person looks at a graph and say’s “Yup, these will sound just as good as those”.

I urge everyone to take the opportunity and go to your nearest Sennheiser retailer and do a side by side listening comparison between the HD600 and the HD800S to better understand what you can gain. It’s much more than one would expect from comparing their graphs on a piece of paper.

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