Headphone and Headset Measurement Seminar Sean Olive

171030_HeadphoneMeasurementSeminar_Photo_Sean

Sean Olive, Acoustic Research Fellow at Harman International and past AES President, presented what amounts to a recap of the last five years of research in developing a target response curve for headphones. A lot of it was familiar territory for me, but there were a number of tasty new tid-bits in his talk.

The thing that always strikes me when I look at Sean's research is how excruciatingly slow and methodical it is. For a long time I've thought that good headphones should sound like good speakers in a good room—as much as possible given the starkly different acoustic environment. Well, it's one thing to say that, it's something else entirely to prove it scientifically.

Over the last five years the Harman group has published fourteen papers on various aspects of the developing a standardized target curve for headphones. For every step forward in developing the target curve, additional steps must be taken to test for errors in the current conclusions. Thank goodness Harman has been willing to do the work...I'd never have the patience. Here's just a few things they've done to build a compelling case:

  • Blind testing with headphones is difficult because the listener can often tell which headphone they are listening to by the fit and ergonomics of the headphones. Harman has developed a way to synthesize the sound of various headphone on a single model test headphone allowing them to switch between the sonic character of the virtualized headphones quickly.
  • Then they had to do a significant amount of subjective blind testing just to be sure the results from the real vs. virtualized headphones tests had real correlation.
  • All along the way to developing the target curve, listening tests were performed, and results analysed and sorted by demographic groups. Age, gender, cultural background, and listening expertise were all tested for commonality in listening preferences. Findings show remarkable consistency in results with some minor exceptions. (i.e. Trained listeners had more consistant results, and they graded harder than untrained listeners. Older listeners preferred less bass and more treble, possibly due to hearing loss. Collage student and untrained listeners preferred more bass than trained listeners.)
  • Test results were examined for potential errors due to imperfect seal. This was looked at in particular detail for IEMs and tests were repeated a number of times with and without controls for insuring seal and loudness.
  • Target curve preference was tested a number of times with people being able to control bass and treble levels for best subjective response. This was done to tweak the target curves being developed.
  • During subjective tests it's important to limit the number of headphones being presented in the test to reduce listener fatigue from evaluating too many headphones. Usually listeners were exposed to about five headphones in any given test session. They found that there is some effect on session results depending on the sonic character of other samples in the array of headphones under test.

It goes on and on and on. Here's a few new nuggets of information I really enjoyed.

171030_HeadphoneMeasurementSeminar_Photo_HarmanPinna

Laboratory pinna developed to make on-ear headphones seal more easily but still deliver response close to a human ear.

Using ten different headphones and measurements for eight people with mics placed at their ear drum, Todd Welti developed a laboratory pinna that could provide a more reliable seal than the standard pinna, and deliver a response more representative of real human ear. Again, I'll refer you to the presentation papers hosted by Listen Inc; the page of response plots used to develop this pinna are quite informative.

171030_HeadphoneMeasurementSeminar_Graph_ModifiedHarmanTargetOEHeadphones

Ear drum reference point response plots for: green dashed line - speaker EQed to have a flat in-room response; black - previous Harman headphone target response; blue - revised target response developed through subjective testing.

The previously developed Harman target response has now been blind tested with a variety of listeners able to adjust bass and treble levels. These tests allowed the Harman researchers to home in on a more accurate subjectively tested curve.

171030_HeadphoneMeasurementSeminar_Graph_HarmanTargetIEMs

Black - original Harman Target for around ear headphones; red dotted - modified AE headphone target; blue - new IEM target response curve.

As promised, Sean et. al. have been working on a target response curve for IEMs. Again, lots more detail in the presentation, but it was found that people prefer about 4-6dB more bass in IEMs (at the ear drum reference point) than for around-ear and over-ear headphones.

This makes sense to me. Even though the effect is small, it seem to me that over-ear, and to a lesser extent on-ear headphones provide some visceral, tactile, and/or bone conducted low frequency information. With IEMs you're out of luck...it's just the ear drum wiggling. Just my opinion, of course, maybe in three years Sean will will offer an authoritative explanation.

A Very Big Thank You!
I can't even begin to tell you how exciting...and frightening...it is to begin a deeper dive into headphone measurements. I'm very grateful Listen Inc. has decided to help me out developing a more informative InnerFidelity headphone measurement program.

The headphone measurement seminar was an eye opener in many ways; it's truly enlightening to be exposed to the very difficult and precise work being done by Listen Inc, G.R.A.S., and Harman. A humbling experience...I've got a lot to learn.

If you have a deep interest in headphone measurements, I suggest attending one of the headphone measurements seminars held by Listen Inc. Keep an eye out for future events here.

I'll leave you with Listen Inc.'s video about the headphone measurement seminar.

COMMENTS
jim in cheyenne's picture

This is great news! Yeah it's time to update the equipment.

How to bridge between the old measurements and the new? You will have better ideas than I, but I would think a half dozen or so well chosen headphones, from modest to 'all-out' with carful discussion of the differences would suffice. Of couse all of us hope than half dozen includes our favorite....

Good luck, keep up the good work!

jim in cheyenne's picture

This is great news! Yeah it's time to update the equipment.

How to bridge between the old measurements and the new? You will have better ideas than I, but I would think a half dozen or so well chosen headphones, from modest to 'all-out' with carful discussion of the differences would suffice. Of couse all of us hope than half dozen includes our favorite....

Good luck, keep up the good work!

Oops, I tried to register, but Listen wouln'd accept it
Is ther some 'company' we are supposed to use?

JMB's picture

I quite appreciate the progress in Grass design. Our ear canals and pinnae are quite variable (even between one owns left and right ones) so exactly which would be the one to choose? Also the materials used to make artificial ears/heads are quite different to our tissues (especially regarding damping and resonance behavior). So there will be an ever changing improvement for more realistic ears (upgrade for ever like we do our toys).
I still have a more basic question about how measurements at the eardrum are relevant for headphones but not for loudspeakers. I understand that IEMs don not use our outer ear and only a part of the ear canal but that does not apply to circumaural headphones which leave the function of the ear canal and at least partially the outer ear intact as would listening to loudspeaker in free air. Basically this is a question about what is the right compensation curve.

coastman25's picture

Surely, the obvious candidates for revaluation using the new testing methods and equipment would be your current wall of fame headphones. However before going there perhaps look at models were the test results did not match your listening experience and see if that is still the case with the Listen Inc system. Then some visa a versa ie re-test some you are familiar with I know for sure your listening experience matches your current test results.

GTABC's picture

That would make the most sense to start.

I'm really interested in the subjectively poor headphones with good measurements(under the old methodology) along with subjectively good headphones with bad measurements (under the old methodology).

Gosh it would be nice if new measurement equipment/ techniques changed measurements in such a way that they would more often be aligned with subjective impressions.

I've often heard that headphones that measure poorly rarely sound good but that there are many examples of headphones that measure well but sound awful.

100VoltTube's picture

I would also love to see some more measurements of those types of headphones. In addition, it might also be interesting to see more measurements of headphones where the measurements tell one story about the sound signature and the listening tells a different one. For example, the beyer T70

100VoltTube's picture

It might be interesting to look at Fourier transforms of the headphones' output as a function of input frequency. A sort of 3D Fourier transform, if you will (or just a couple of normal Fourier plots). It might also be interesting to see how the distortion components change during the decay of a tone. Like a CSD plot, but the decay of a single sine wave.

Journeyman's picture

I do hope they help you out. It's great advertising in the long run given the fact you are a reference for many headphone enthusiasts.
I also think the headphone community would be very grateful.
Tyll I do hope you measure some Beyerdynamic Headphones models again. :-D I know you don't really like them but the DT880 is a reference for many people.

MRC01's picture

What a treat. It's great to see this level of research which will improve SOTA for everyone. Thanks for sharing the experience. As for what kind of new measurements to include, I suggest CSD plots.

zobel's picture

I imagine that the new distortion / noise measurements may be the biggest improvement in conveying perceived sound quality. Those, along with the waterfall plot, and improved SPL/freq. graph, there has to be be a much improved set of measurements that will go much further in describing the sonic features of all HP measured.

Thanks for keeping your tests as relevant as possible Tyll. I like your idea of covering the 'worthy' cans and letting the unwashed hoard go as is.

thu hien's picture
bobusn's picture

No excuses! Thanks for your dedication, Tyll!

maitrishah's picture

Thanks for posting. The article more or less says it all.
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