Evidence of Headphone Break-In? Page 2

The Break-In Data
Let's first take a look at the full spectrum data from 10Hz to 22kHz for the left and the right channel.


Fig. 1 Show the left channel frequency response differences over 90 hours. If there were no differences from one measurement to the next, the result would be a straight line. With the exception of the large spike at about 12500Hz all changes between measurements lies between +/- 1dB. This is a fairly small amount of change across the board.


Fig. 2 shows the right channel frequency response differences. Please note a few things:

  • Both graphs have the data normalized to zero at 300Hz. This frequency was chosen because the data shows little difference between data-sets occur in this area.
  • Both graphs show the low frequencies slowly rising in amplitude.
  • Both graphs show the largest differences occur from roughly 5kHz and up.
  • Both graphs show erratic behavior around the fundamental driver resonance at about 80Hz, and at between 800Hz and 2000Hz.
  • You'll have to look very carefully (we'll take a closer look in a minute) but in both graphs something discontinuous happens at the 20 hour mark (light blue line).
Let's start with a closer look at the highs:


Fig. 3 Shows frequency response between 3000Hz and 20000Hz for the left channel.


Fig. 4 Shows frequency response between 3000Hz and 20000Hz for the right channel.

In figures 3 and 4 the changes in the high frequencies trend in one direction with the exception of the 20 and 40 hour mark. My tendency is to believe these data could easily indicate slow changes in position. The problem is the 20 and 40 hour data shows what would indicate movement in a reversed direction, and then the 65 hour mark goes back in the original direction. I would expect gravity or the spring tension in the headband to cause changes to all move in the same direction over time.

Let's look at the low end of the scale.
Fig. 5 shows a close up view of the left channel FR differences over time in the range between 20Hz and 300Hz.


Fig. 6 shows a close up view of the right channel FR differences over time in the range between 20Hz and 300Hz.

The gradual slightly increasing bass response could certainly be the seal of the headphone getting slowly better over time as the cushions seat against the head. However, at the 20 and 40 hour mark significant changes occur at about 80Hz; this is the fundamental driver resonance point. I don't think these data could me made by position change; at this frequency, FR changes due to position are from the changes of the seal and are not very frequency selective. These changes can really only be attributed to something happening with the driver during the 20-40 hour time period. I'd say this may be evidence of driver break-in.

Here's a closer look at this frequency response area:


Fig. 7 shows a close up view of the left channel FR differences over time in the range between 60Hz and 180Hz.


Fig. 8 shows a close up view of the right channel FR differences over time in the range between 60Hz and 180Hz.

Here again we see the 20 hour curve doing something odd. You'll also notice that in both channels, the curve at 20 hours is similar shape, but larger in amplitude than the 65 hour curve. Indicating to me that something happens to the drive at around this point that changes it's character and then it settles into a new norm.

And then there's this stuff up around 1000Hz.


Fig. 9 shows a close up view of the left channel FR differences over time in the range between 800Hz and 2000Hz.


Fig. 10 shows a close up view of the right channel FR differences over time in the range between 800Hz and 2000Hz.

Something very different about the 20 hour curve, that's for sure.

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COMMENTS
Gatepc's picture

Great article I love that you really got into the details. Can you confirm if these are in fact the same drivers inside the K701/702s?

Oh what would be great is if you managed to test some high end cables in as much detail as this. You know the ones that are sparkled with fairy dust and dipped in the liquified remains of extinct animals? I think that would be very interesting.

Thanks for the post.

dalethorn's picture

Those spikes in the chart are most likely Quincy's telepathic reaction ("ouch") to all of that pink noise. For break-in I generally take the Pasadena Symphony's binaural recording of ASZ (first segment 1m 56s), set it to loop, turn up the volume, and let it play for a few hours. If nothing else, it'll warm up the voice coils pretty well.

xnor's picture

Three literally (well, one so far) smokin' hot Q701s to experiment on? The guys at AKG don't know who they're dealing with. *dr-evil-maniacal-laugh*

Nah, jokes aside. I really like the article, especially the summary surprised me. Only a fool would jump to conclusions but you pose a couple of very interesting questions instead and animating your readers to think for themselves.
While the changes you measured definitely exist and are supported by the trends we have to keep in mind how small they actually are. Half a dB here, quarter of an ohm there - audibility is questionable or at least very far from those unrealistic claims made in other forums. Still, those measurements are quite an accomplishment and exactly what I had hoped for a year ago in the measurements lab thread.

Hmm, actually all I wanted to post was a simple "first" but looks like I'm getting old and slow so I had to write a few more lines. If you read my bo.. eh amazing post, that only can win, to this point you should know that I'm giving my prize to the second best poster, hah! :-P

Tyll Hertsens's picture
... but that's okay.

The data is stimulating, don't you think?

:)

maverickronin's picture

Did you run the full suite of tests at each point in time, only the ones that you had graphs of, or did you only show graphs of the data that changed much over time?

I ask because it always seemed to make sense to me that the greatest changes would be at the limits of the diaphragm's excursion and that (I think) would be best measured by a low frequency square wave. Am I on the right track or do the THD+N numbers encapsulate that as well?

maverickronin's picture

Now that the full reports are up and I've had a chance to look at them there seem to be some slight fluctuations in the amount of overshoot on the 30hz wave forms but it mostly goes back and forth so it doesn't look like any firm conclusions about break in existing can be made from that data either.

Shike's picture

Unlike the headphones, I much enjoyed seeing you run pink noise through them for the sake of at least trying to get to the core of the burn-in argument.

The problem, unfortunately, is this is only one down. The curse this headphone has left is one you and your inbox will feel, as people start questioning whether their own headphones burn-in. "Do the HD800, HE6, LCD-2" they'll cry. The 701's will be long gone, but you will be stuck with requests locking you up in the measuring chamber for eternity.

Oh, and Gatepc forgot the main ingredient for boutique cables: virgin tears gathered on the top of the Himalayas . . . that's how they achieve "quantum tunneling" you know?

Currawong's picture

It's almost amazing that it has taken so long to do some measurements like this. What would be interesting now is if you found two different pairs with one supposedly having a lot more bass than the other and measured their frequency response.

Fred76's picture

Would be interesting to do the same experiment with amps and/or DACs, by ear my DIY gear has usually taken 5 to 10 hours before the low frequencies started to kick in, many don't believe in capacitor break-in though.

LFF's picture

STOP IT TYLL!!!! STOP!!!!!!

Was having a conversation about this on Saturday! I was commenting to another head-fi'er that I wished you would do an article on burn-in and see what the measurements said.

I check this the next day and BAM! Wish granted. Awesome job by the way and the depth of analysis is fantastic. Loved reading the article.

I'm off to tell another head-fi'er how I wish you will give me a pair of the Q701's to fill the hole left by my HF-1's. :-p

goldstarsteve's picture

Hi,

I don't normally rush to comment but if the prospect is a free Q701 I will not only comment but even run the spell checker for you,

Anyway I wanted to suggest you try some controls. For example try measuring several times in a one hour period and plotting it to see what happens. Try taping the headphones in place with sellotape (seriously), try same experiment on different headphones that you don't think need to break in and most importantly - run same set of measurements on headphone you have "broken in" and see if you continue to get these weird changes. Why weird - because there is no scientific reason for break in to occur with headphones so my guess is we are seeing some kind of noise here but I am not sure where from (your equipment, movement, whatever...).

All power to your new site and I appreciate the combination of measurements with your subjective listening. I would like to see an article on how to match headphone curves to speaker curves so that one can know which kind of headphones sound similar sonically to speakers one likes. I don't think this has ever been done before - it is an interesting idea to develop.

Cheers

Steve

Tyll Hertsens's picture
Sorry I forgot this link, the full measurement spreadsheets for the entire test is here. Article updated.

Thanks for all the comments folks!

Tyll Hertsens's picture
The scale is wrong on the THD measurements.

I will fix the page, but will place a copy of the previously published erroneous THD data here.

Duh.

________________________________________________

Total Harmonic Distortion + noise Differences
Let's look at differences in Total Harmonic distortion. These are differences over time in %THD+noise at the 100dB setting.


Fig. 11 shows the difference over time for the left channel THD+noise at 100dB vs. frequency.


Fig. 12 shows the difference over time for the right channel THD+noise at 100dB vs. frequency.

Some expanded views:


Fig. 13 shows the difference over time for the left channel THD+noise at 100dB between 10Hz and 220Hz.


Fig. 14 shows the difference over time for the right channel THD+noise at 100dB between 10Hz and 220Hz.

Notice the features between 25Hz and 35Hz. Total guess here, but at this low frequency we might be seeing the diaphragm material breaking-in and changing its resistance to bending at the excursion extremes.

Now note the feature at around 200Hz on both charts. I have no idea what it is. I can tell you the weird data points at 220Hz is the meter in the AP changing ranges and creating a measurement artifact.

I also measured the difference in impedance


Fig. 15 shows the difference over time for the left channel impedance.

Here you can see the generally moving trend with time, and the exception of the data set at the 20 hour mark (light blue).

Summary Did I show break-in exists? No. There are too many variables still. Was it simply movement? I don't know. If I did it again to another brand new pair would I get the same results? I don't know. If I did it to an already broken in pair would I get the same results? I don't know.

What I do know is that during the course of these measurements some things changed. While the data showed only very small differences, the data was clearly above the noise, and a general trend observable. The data also showed a discontinuity around the 20 hour mark in both the FR and THD data. While, it seems to me, much of the change observed could easily be due to movement, especially in the frequencies above 5kHz, some changes seem more likely due to break-in. In particular, the changes in frequency response around the fundamental resonance of the driver at 80Hz, and in %THD+noise at the same frequency and at around 25Hz.

There were also things I have no idea about: the changes in FR at around 1100Hz; and the THD change at around 200Hz.

The full measurement spreadsheets for the entire test is here.

Alrighty then, time for some fun, let's give away a pair of broken-in Quincy Jones Q701s. Within the next month or two, I will be willing to set the chamber and test system aside again for another four day experiment. Between now and the time I publish the next article, I will be reading the comments here. The comment I find most enjoyable (could be technical ... could just be funny) will win a Q701.

Have fun!

Stirrio's picture

There once was a man from Waukegon
Whose headphones took too long to break in.
So he listened and moaned
Till the sound of his 'phones
Got him up off his chair and butt-shakin'.

dalethorn's picture

So today I got a second set of the $50 (or is it $59?) Beyer DTX-300p 'phones, this time in white. I was very curious about break-in since my red set was fully broken in. I figured that at least in this price range I should hear something, a difference in response, driver matching, i.e. Q/C variations et al. Nothing. I use mostly 320k CBR MP3's with a lot of detail across the freq. and dynamics ranges. Nothing. I couldn't detect a sliver of difference, and that's interesting for the Q/C aspect if nothing else.

Yoga Flame's picture

Thanks for doing this. Great job again, as usual.

When all the measurements are done, might I suggest playing the same song through both the burned-in and pristine headphones, and recording the results. Then use Audio DiffMaker to create an audio file carrying only the differences between the two.

The numbers so far show some differences as burn-in (and possibly other factors) takes effect. As you noted, the numbers are small. But are they too small to be heard? For those of us who aren't great with numbers, a wav file or YouTube audio clip of the actual difference might resonate (heh) better.

Simeon718's picture

I have a pair of headphones for dubstep, now I just need a pair for my classical music. [Paradox? You decide!]

Buyer no 1's picture

Great test!

Guess after 20 hours you needed some fresh air, opened a window, and then changed the air pressure in the room, thereby changing the sealing of the HP..... ;-)

svyr's picture

Tyll,

Nice job with the Q701s... Like the rest of the lurkers from head-fi I was also curious about someone providing detailed measurements of the hp FR, THD+N vs length of the break-in...

Tyll, it would really help if you didn't try to map 10 data sets on one chart that ends up looking like a fruit salad. (higher res graphics might also be useful... I know headphone.com still makes really tiny graphs, but the web has sort of moved on and on 1920x1200 screens it looks tiny and blurry )

Perhaps supplementing the existing plots with plots of (say) the start, 5h, 20h, 65h would be more illustrative. Or maybe start 20h, 65h separately. It'd also be interesting to see a plot of the last 3-4 sets, to figure out whether the headphones settle on an end frequency or not. (although your interpretation seems to suggest it's just moving about, not settling?)

It would be nice to see measurements of the same pair after a few days/weeks(?) of 'cool-off' after the final measurement, since some people say break-in goes away ;) .

I'd also be curious to know whether the pair permanently sits on the measuring set-up (and how tightly it's fixed to it :D? ) or it might move off a bit if you put it on differently each time (or slide off if it's not quite attached firmly), and what the resolution and accuracy of the measuring gear/(perhaps)number of runs per each measurement to average are? (since on some plots we're talking 0.1db differences).

This is a bad example, but while debugging my old SRM-1/mk2 I at some point measured L-/L+ voltages on 1khz tones (w a fluke RMS 187 multimeter. Not perfect but ok) and there was random but persistent(?) drift of about 1-2v for around 280v measured L-L+ signal voltages. (although in retrospect with the quoted accuracy for AC of ± (0.4%+40) that sounds about right :D )

svyr's picture

oh, the other thing is, how much of the difference measured is attributable to variation in the output of whatever is driving the Q701? (amp warm up, thermal drift, mains voltage fluctuation, etc) (perhaps the same question for the measuring equipment)

>What would be interesting now is if you found two different pairs with one supposedly having a lot more bass than the other and measured their frequency response.

Why? Wouldn't he attribute that more to unit variation of the Q701 drivers, etc Or do you mean the owner thinking his pair is burned in and as some head-fiers say 'omg-the-bass-liek-rly-bloomed' (cough-placebo) :D ?

Finally, I don't like the title of the page for the article: "Evidence of hp burn-in"...It's more of a set of measurements and a discussion of... As the summary suggests: 'Did I show break-in exists? No. '

Tyll Hertsens's picture
"Finally, I don't like the title of the page for the article: "Evidence of hp burn-in"...It's more of a set of measurements and a discussion of"

So I added a question mark.

svyr's picture

:) lol... Was it there before and I haven't noticed, or do you mean you just did?

PS edited the first two posts a bit, clarifying some things. Please re-read.

PPS questioning in this case seems to be a lot easier than measuring ;) ...

Although, the magnitude measured makes me somewhat pleased re: what people a lot of time claim with burn in for their HP (the 'omg the bass is so sick now' argument)... Still, maybe it could be different for other HP ;) :D

Tyll Hertsens's picture
On your comment:

"I'd also be curious to know whether the pair permanently sits on the measuring set-up (and how tightly it's fixed to it :D? ) or it might move off a bit if you put it on differently each time (or slide off if it's not quite attached firmly), and what the resolution and accuracy of the measuring gear/(perhaps)number of runs per each measurement to average are? (since on some plots we're talking 0.1db differences)."

The headphones just sit on the head like normal and are not moved during the whole test. The door to the chamber is closed during the entire test over four days. The APs measurement resolution and accuracy is high enough to show the data trends, but if you look closely on some graphs you can see the resolution limit. When each data point is acquired, it takes a bunch of measurements and waits for the measurement to settle. There are a variety of settling algorithms available, the one I use looks for measurements settling in an asymptotic pattern and once it reaches a certain settled value, it takes three readings and averages them.

svyr's picture

does it account for pads wear-in over the longer time in the test :P?

svyr's picture

PPS to that on the subject of measured magnitudes ;) . On the AUDIBLE burn-in claim 'and blooming post burn-in bass'. I find it very hard (impossible) to even tell less than 0.5dB volume difference side by side on the ABX test site when I have the opportunity to compare to samples of both.

YMMV with golden ears?

trickztastic's picture

If I don't win the AKG q701's, I'm gonna break-in somebody's face. I'm looking at you Bret Michaels.

3DPRO's picture

great article Tyll!

The detail of your experiment is really great. My brain just exploded after reading this.

seriously.

hehe. :P

and I downloaded the spreadsheet to read on the train to my class tomorrow. it's gonna be fun!

dvltn's picture

I read this entire article and found no facts to support that your headphone nor living quarters were broken into. There is no mention-of or evidence of robbery, forced entry, nor burglary. This is extremely misleading.

dalethorn's picture

Good thing there wasn't a burn-in. That would be playing with fire.

DrL's picture

... I'm wondering if the phenomenon of break-in, or what people perceive as break-in, may have more to due with one getting used to the sound of a particular headphone than an actual physical change... I mean, I've had similar experiences with many music albums - they sound ok at first, but they keep getting better and better every time I play them...

An interesting experiment would be to give two groups of people a K701 (or Q701 or another headphone) and ask them to judge how much the headphone's sound change over time. One group would be given brand-new headphones and the other group would be given headphones with several hundreds of hours on them. Obviously, the test persons would be unaware of which group they were in. That should make for an interesting comparison. Maybe AKG would be willing to sponsor even more headphones for the noble cause :-)

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