Important Reading for Headphone Measurement and DIY Geeks

Holy Moly! Been reading a lot lately on headphone design...how much is actually getting absorbed as knowledge in my brain is another story entirely. This. Stuff. Is. Complicated.

It's come to my attention over the last week or so as I've been working on my review of the Philips Fidelio X2 that my understanding of headphone measurements is severely lacking. For example, I had been making the assumption that that when we find the right target curve for headphones, it would have some sort of elegant beauty, and that it would be broadly applicable.

And then I got the X2.

This is a very good headphone as I'll soon report, but to my layman's eyes (a fairly sophisticated layman, but still not a headphone engineer) the measurements of the X2 looked worse than the X1. And yet, when I listen, the X2 is clearly superior. I spent some time exchanging emails with one of Philips' headphone engineers, and have come to the conclusion that the issues we're dealing with here are just horrifyingly complex. Headphones are way more complicated than speakers in terms of the acoustic problems that need to be addressed.

I don't think now is the time to get into it, but I did want interested InnerFidelity readers to have the opportunity to begin to delve into the subject. I will in future be writing Headphone 101 articles on the subject of headphone acoustics---as I am able to digest the information and re-write it in a simplified form---but I think those of you who have a deep interest in such matters would be well served by accessing the real thing.

The first is a tutorial presented at AES 120, Paris, May 2006 called "Headphone Fundimentals" by Carl Poldy. You can find it here.

The second, also written by Poldy, is chapter 14 of "The Loudspeaker and Headphone Handbook." This is a very expensive book with only one chapter on headphones, but that chapter is about 100 pages long. If you do a Google search for "Loudspeaker and Headphone Handbook" you'll find this link. I think you may have to have a gmail account for it to work, or you may have to do your own Google search to come up with a link that's valid for you, but it is the entire book.

Good luck in your reading. If you're like me there'll be a lot of head scratching in it, but it should be wortwhile---the material is top-notch.

COMMENTS
johnjen's picture

Wow that some spicy meat balls!

Those 2 tomes will take some serious head crunching time…
Perhaps 1 section at a time will keep my eyes from glazing over prematurely.

Thanks for the reference material and filling up my reading list! :thumb

JJ

Impulse's picture

Stop teasing us about the X2! First you said they seemed to measure similarly (or sound similarly, I forget the exact quote from HeadFi), and now it measures worse but sounds better??

I'm just kidding around, I wouldn't hold you to stick to or absolutely nail any initial impression or anything of the sort, but I AM pretty excited about the X2... Looking forward to that review.

ultrabike's picture
Haven't finished reading that either... :(
Jazz Casual's picture

For some unknown reason Tyll's epiphany doesn't come as a surprise to me.

Three Toes of Fury's picture

Yo Captain Headphones,

Thanks for the links! AHHHHHH! an electronic copy of the oft-referenced "Loudspeaker and Headphone Handbook"!?! AHHHH!

Absolutely appreciate the opportunity to learn more.

Keep up the great work dude.

Peace .n. Living In Stereo

3ToF.

Hal Espen's picture

What a coincidence — I'm currently immersed in the fiendish complexity of re-reading James Joyce's Ulysses. The hero is Leopold Bloom, and his wife Molly's pet name for him is "Poldy."

Anyway, I feel your pain! It's an extremely sobering thing when Tyll Hertsens writes that "my understanding of headphone measurements is severely lacking." What hope can there be for the rest of us?

SkylarGray's picture

Measurements of audio devices—especially headphones—can be incredibly misleading. They are *so* easy to misinterpret.

This is, in part, because we do not have a complete understanding of how our perception system (brain) processes the incoming signals (sound/music/etc.). Does the brain compensate for the ear canal "transfer function" or not? Does the brain compensate for pinnae "coloration" or not? To what extent if so? Is the brain subject to errors in any compensation that may be happening? Are HRTFs meaningful?

There is no consensus between experts on these questions or at least no complete answers. And this is only scratching the surface.

Unfortunately, our measurement hardware and software functions on incomplete and possibly incorrect perceptual models of how our hearing works.

So measurements work best as *relative* guides and not absolute characterization. When I design headphones, I rely on measurement tools every day as a sort of compass to point me in a direction; I can then explore that direction by iterating my driver design/acoustic configuration/material selection/etc. and use measurements to tell me how far I've gone down that path by making a relative comparison to a previous measurement. Though I am diligent, methodical, and use 10's of thousands of dollars worth of equipment, my measurements are mostly useless to everyone except me.

Ultimately, the listening experience trumps all measurements. As a listener, ask the question "Do I like the way these headphones sound, fit, and look? Am I having a good time?"

Tyll, your commentary, ruminations, and documentation of your experiences are all the real reason we keep coming back here. I am sincerely impressed by your pursuit to improve while also being an educator for the headphone-enthused. Please keep up the good work.

P.S. My subject line is nicked from John Atkinson's excellent seminar "Loudspeaker Measurements Explained."
https://www.youtube.com/watch?v=j77VKw9Kx6U

Three Toes of Fury's picture

Very good points and observations. And i do agree that the listening experience trumps all....however...im not sure i fully get why the variable of "sound" is not, for the most part, easily quantifiable?

I would think the process of measuring, electrically, the sound quality of headphones would come down to two key variables: test rig and gathering/interpreting the right data.

For the rig, i would think a reasonable facsimile of the human ear would be created. Outer ear, canal, and a high quality microphone membrane simulating the eardrum. From a data standpoint we would know the specific driving frequency that we are trying to convey and would be able to compare input to output.

Taking a different approach...one that accounts for the human factor...couldnt a large data set from a wide array of headphones be studied for specific data signatures that are consistent in the headphones most often rated as great?

I know my comments are pretty naive and that at then end of the day there will always be the human interpretation which can differ from person to person however i would think there's enough concrete data available to help ensure designers are indeed on the right path....thou...i suppose thats exactly your point with the "pointing you in the right direction".

Anyhoo...thanks again bunches for your comments. Sounds like you have first hand knowledge of designing headphones...would love to hear more about your experiences, observations, process, etc.

Peace .n. Living in Stereo

3ToF

Tyll Hertsens's picture
I believe Skylar is designing a headphone for AudioQuest at the moment. I did see a prototype of these cans at CES last year...they're quite interesting and innovative. I very much look forward to the release of these headphones.

And thanks, Skylar, great comments.

Jay_WJ's picture

While I perhaps understand what you truly mean as a headphone designer, I think your writing has a bit too strong statements. Listening experience AND measurements are both important. Without measurements, you cannot design headphones the way you are doing now. And measurements CAN be interpreted properly by ones with suitable technical background and knowledge of the measurement setup being used, plus experience as well. They CAN be useful even if generated by someone else, especially if there are a lot of different headphones' measurements generated in an identical condition and by a consistent process like Inner Fidelity or HeadRoom.

Jazz Casual's picture

Nicely put. I've not watched the seminar yet but I think this Stereophile article by John Atkinson may be based on it. I've sent it to a couple of prominent Head-Fi'ers for their edification. ;)

http://www.stereophile.com/features/99/

and this too: http://www.stereophile.com/features/808head/index.html

Jazz Casual's picture

I should have addressed my previous post to SkylarGray as it was a direct reply to his first post. This site continues to behave oddly.

hutnicks's picture

I would also suggest looking into Evelyn Glennies dissertations on how we actually hear. More manufacturers should really be consulting her .

balkanguy's picture

Headphone design, like speaker design, is extremely easy. You simply use your EARS! The graphs and decay plots and things are HELPFUL once you find what SOUNDS the best of what you have tried, so you can get an idea which ones are worth further investigation.

For example, I notice a gently smooth descending curve, typically referred 2 in PA circles as 'room EQ' sounds best with just about everything. 'Flat response' is ALWAYS way 2 bright IMHO. Also keep in mind that DISTORTION and COMPRESSION will BOTH make a given sound B percieved as LOUDER than it is in terms of graph results, so if a phone has a 'flat' curve, but a lot of DISTORTION in a particular range, it is the same PERCEPTUALLY as a big hump or spike in that region (depending on how the distortion &/or compression artifacts R distributed).

The current leader in headphone design regardless of price is the $15 Koss KEB15i. The tips are garbage, so use the tips from the Auvio 'for android' model, 'Element', or 'Pearl Buds 2.0' for an infinitely better seal (good bass) & comfortable fit =) DONE! EXCEPT U cannot get ideal ANGLE on them because the FORM FACTOR is krap, but they R STILL better than N E competitors with this combination. What is needed is 2 take that DRIVER/FILTER assembly & put it in a better FORM FACTOR (& without the mic / remote garbage).

That is what I am in the process of negotiating right now, as the Chinese manufacturer of the Pearl Buds (1.0) seems 2 have no interest in fixing their 60% defect rate (but when they DO work right, they R the absolute leader). N E 1 interested in contributing 2 this project or with some help in marketing or whatever else contact me at 'zhotstuff at hotmail dot com' =) I just go out there & try everything, regardless of price. Clowns like 'Joker' on 'Head-Fi' obvioiusly have zero taste, always promoting distorted, nasty highs of armature & weak whimpy krap bass designs instead of 'full range' awesomeness that I (& most people) prefer.

Just because he has a bunch of blogs ranking his 300 or so tryouts does not mean he is correct. I know 4 a fact many of his reviews R lies, things he has obviously never tried, as some of the things he says have nothing 2 do with the actual sound of the products I have personally verified through audition.

balkanguy's picture

On the HeadFi web site there is a dood who calls himself 'Joker', & is playing a joke on the uninformed, rather like the guy 'Scott Grove' on Youtube talx endless about guitars, collecting a bunch of set neck all mahogany instruments, admitting his all time favorite is also a set neck all mahogany instrument, yet claims wood has nothing 2 do with the sound quality of an electric guitar. He is something of a 'mental vandal', spreading damage 4 kix! I C 'Joker' the same way. Like 4 instance I just checked his personal tryouts history & there R only 3 models of Koss on it. Now, given the fact I have personally verified tha tprice has absolutely ZERO to do with teh sound quality of headphones, he should @ least try other models in their range. The Portas certainly sound leagues better than those 'on-ear clips' that 'InnerFi Man' here has on his 'Wall Of Fame'. This is all Joker has looked into:

-Koss KEB70
-Koss Pro DJ100
-Koss UR55

Go here & C 4 ya'self!...

http://www.head-fi.org/u/118389/ljokerl

What a freaking JOKE! When a manufacturer produces ANYTHING that is of high quality, U really owe it 2 ya'self 2 check out the rest of their line. Like Maxell or many other brands (Auvio name being another), there is no 'house sound' & each model can sound radically different from the next. The Koss KEB15i is currently the best headpone that exists, regardless of form factor, regardless of design. There will B the fluke here & there, such as the old Auvio Pearl Bud design, but their QC is so far down the toilet it's a crap shoot (pun intended =)) IF ANYBODY OUT THERE KNOWS OF ANY IN-EAR OR HELL, ANY OTHER DESIGN THAT SOUNDS BETTER THAN THE KOSS KEB15i, BY ALL MEANS CONTACT ME AND LET ME KNOW WHAT IT IS!! =8^D U can mail me at 'zhotstuff at hotmail dot com'. Thanx peoples! =) Happy listening! Oh & of course, as stated in my previous post, the stock tips W/the Koss R totally UNUSABLE & RUIN the sound. Must use alternate brand & model tips as listed previously. Yes in other words, this Korean import has high performance BY ACCIDENT = ideal 4 refinement into something even more special =D

Seth195208's picture

Yikes?

bronson's picture

Wooah, slow down already, what?

You're saying this is the BEST "headphone" that exists? (It's an earphone though?!)

http://www.compbargains.com/_e/Headsets_Earsets/sproduct/1027405363/Koss...

What's going on here, have I missed something?

Or is Tyll hiring performance art to jazz up the comments section now?

Jazz Casual's picture

Yep. That's definitely a Yikes!

TheTalbotHound's picture

I really hope this will mean that more information is added to the data sheets. Maybe CSD and acoustic phase.

tony's picture

RMAF presents you to the Seminar followers , like me .
Hmm , I wonder if JA is feeling a bit nervous over Society's promoting you ? or are you actually "Editor in Chief" in Stereophile's estimation too ?
Well , anyway , I probably wouldn't bother with Stereophile and their Vinyl outlook of things except for our Tyll and perhaps JI and his MSB Analog Dac ( something you should probably have sitting on your review desk , in a nice color scheme to match your many Shirts ) . You already have that $80,000 Measuring Head thing . You might as well have a loaner MSB if you are to properly evaluate those beautiful transducers . Me-thinks !
I hope the Sony people slide a Walkman A17 into your pocket at RMAF , this thing looks to take the world by storm or dare I say by 16/44.1 - 24/96 , no DSD , even though DSD is a Sony creation . Guess this shows that DSD is dead for all practical purposes , too bad for Cookie and her small crowd at Blue Coast and too bad for Apple portable owners , the iPod will loose half it's used Value on ebay as the A17 rolls out in November . Sell you iPods now , you've been warned .
It seems that there is probably no longer a pressing need for the lesser digital formats like MP3 and such , everyone now has the bandwidth to support Red Book or the bigger 24/96 files , the headphones and amps can deliver the performance levels , what's left ? , Style ? , seems like we have it all .
Congrads on you're promotion , if thats what it is .

Tony in Michigan

thune's picture

Just look at Sony Pure Audio to see where Sony is coming from: DRM laden disks. To them the HiDef world isn't even portable. Promises of Sony opening their vaults to downloads (http://www.stereophile.com/content/sony-push-hi-rez-downloads) seem to be set back somewhat.

Jay_WJ's picture

I do not agree with the simple sentence telling that headphones are way more complicated than speakers in terms of the acoustic problems that need to be addressed. I kind of understand what you mean, but it would be better to say there ARE different kinds of complexity between designing speakers and headphones.

SkylarGray's picture

Thank you, Jay_WJ. I do agree with everything in your post. Perhaps my statements were strong, but I was careful to say things like "can be incredibly misleading" and "mostly useless." Emphasis added.

I have been meaning to create a devil's advocate follow-up to my previous post celebrating how measurements CAN be useful. Jay_WJ's points are excellent, so I will just add this:

Until Tyll's shoe-store-esque, try-it-before-you-buy-it headphone boutiques have become many and ubiquitous across the globe, it is difficult to audition a set of cans before purchasing. So measurements then become a helpful tool, again, in comparing performance *relative* to other measurements made under the same conditions.

Now to play reverse Devil's advocate:
If an end-user has the opportunity to seriously audition a headphone, what use then are the measurements?

Allow me to present it another way...

• A designer/engineer needs to utilize both measurements and listening to effectively do their job.

• For the end-user, listening is the ideal evaluation "tool." In lieu of listening, measurements plus a trusted review can act as a substitute for personal ears-on experience. Is there a need for both (listening + measurements)?

This last section isn't necessarily my fully-formed opinion—just an open question and topic for discussion.

thune's picture

I'm not sure I see how the "measurements of the X2 look(ed) worse than the X1".
X1 http://www.innerfidelity.com/images/PhilipsFidelioX1.pdf
X2 http://www.innerfidelity.com/images/PhilipsFidelioX2.pdf
The X2 bass push gets out of the way fast, allowing 200-1000khz to be flat, which you seem to like (maybe making this region sound cleaner and maybe less bloaty in the upper bass.) Also, the X2 depression (relative to X1) in the (2.5k)5k-8k region might give it some relative politeness, and you seem to give higher marks to headphones with a more pronounced >~2k shelf.)

I guess the X1 measurements might look better to someone who hasn't spent much time looking at your measurements and reading your reviews. Looking at the X2 measurements I would ask if the relative peak at 4.5k is real and causes listening issues, and why does the X2 demonstrate more positional variance (which the X1 excels at)?

thune's picture

Tyll's X2 review drops 15 minutes after posting the above. Checking it out...

balkanguy's picture

Doesn't matter what the method, the RESULT is the BEST that is currently available. Instead of wasting your time pretending not 2 understand my post, how about U go buy a set of Koss KEB15i & stick some tips from the other sets as described above, so U can then tell me if U have ever heard N E thing better =D I only care about RESULTS. I do not care about price, brand, or form factor (over ear, uncer ear, over there, speakers, whatever) ~ what have YOU ever heard that sounds BETTER? Post here or mail me at 'zhotstuff at hotmail dot com'. Perhaps there is some other no-name Asian phone that is even BETTER & I can remarket THAT =D

balkanguy's picture

I hit the 'reply' button on that troll-tard saying "Slow down a minute" in their post above pretending not 2 understand what I wrote, yet there is no reference 2 their post of N E kind, nor does it include a link 2 it, text from it, or N E thing else! This is a BROKEN blog setup! U should not offer a 'reply' link if it does not 'reply' 2 the post selected! . U shoudl instead just have a 'post' link somewhere, ONCE. Fix the 'reply' feature, or get rid of it alltogether. Second, there does not appear 2 B either an edit or a remove post feature so the user can change or delete their own posts. That is absurd. This blog iformat is EXTREMELY primitive! Better than nothing yes, but a joke by all modern standards, just like (almost) everything from Beats is a joke =))

Seth195208's picture

Yikes?

bronson's picture

definitely "Yikes" for sure.

Unless Halloween has been brought forward this year?

:D

balkanguy's picture

If a beautiful poor girl from (insert wherever here) threw herself @ U FOR FREE (or a cheap date), would U pretend a fat repellant American wench (as is common) is more 'valuable' simply because they R greedy & dedicated 2 blowing all your cash? THAT is the same insanity I C in people choosing audio gear. They think price has some sort of intrinsic value, like it 'must' mean it is good if it is very expensive. It's usually just a SCAM! & expensive doesn't mean better, just like a poor girl can B very pretty, or a greedy or rich one ugly & fat! Price does NOT mean quality. This is a mathematical type of fact people need 2 acknowledge if they R ever 2 find good values in audio =D I just try whatever, regardless of design & stuff, & write detailed notes about each that reveal certain patterns in sonic results. Like all metal tweeters sound krap. All balanced armatures R distorted-sounding, & so on.

U can make your own observations, & I will eventually put all of mine on 2 a page, probalby Indiegogo, with the ideal path 2 perfection =D Please list 4 us your favorite phones & Y U like them, & perhaps InnerFi can set up a 'swap phones' network where people can pit their phones against each other by mailing them 2 each other 4 review & noting their flaws & benefits. It would B very 'boxing match' & entertaining in the sporty 'who will win' aspect of sound competition among real users, not just the 'top down propaganda' of sites & magazines dedicated 2 pleasing their advertising sponsors.

hutnicks's picture

And need to get help ASAP.

Tyll Hertsens's picture
Sorry dude, you're not bringing anything useful to the discussion but continue to post rabidly. You're outta here.
thune's picture

Maybe send a pair of original headphones (with original tips) to joker and include some sets of your preferred tips (new). If he accepts them, then he could forward them to Tyll for measurement. Honestly there are more IEMs than a sane person can possibly listen to, and the amount of digging required is thankless. If you have really found a gem then work to forward it to those with an audience. Just be aware that others experience may not match yours.

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