The nice folks over at AKG decided to send me a bunch of Quincy Jones headphones, including three Q701s! That's good news for both you and me. For me, because it will allow me to do some experiments I've been wanting to do for a long time. The AKG K701, now reborn as the Quincy Jones Q701, is notorious for needing hundreds of hours of break-in before they sound right. I want to see if that can be measured, and in this article I'll show you the first sets of measurements.
It's good news for you, because when all is said and done, I'll give away two pairs of the Q701 headphones to some lucky reader.
So, let's talk about break-in, shall we...
What is Break-In All About?
Separating voodoo from science in the audio world isn't easy. The human hearing system is exquisite, but it also has the annoying habit of learning and changing, so what we hear one day may not be what we hear in the same circumstances the next day. The placebo effect is strong in listening experiences. Was there really a change when you swapped cables? Or were you fooling yourself? It's not easy to tell.
One area where voodoo and science struggle mightily is over the idea that audio products in general, and headphones in this particular case, "break-in" and change over time. This idea seems logical enough for headphones: the new driver in the headphone needs to wiggle around some and exercise its flexures to settle into its norm. Problem is, if you're trying to hear it you only get one shot; once something has hours on it, you can't take them back off to compare. Headphone enthusiasts get one try to listen for changes during break-in of brand new cans, and over-attentive listening is one very likely path to fooling yourself.
I rarely hear break-in. I reckon the diaphragm does change a bit, but by the time it's got a couple of hours on it, it's done settling in. There is one exception in my mind, however, the AKG K701 is notorious for needing long break-in, and I've heard it a number of times. It's got me convinced that there is such a thing as a break-in period for headphones, and some need it more than the others.
I decided to see if it could be measured.
The Experiment
I took a brand spanking new pair of AKG Quincy Jones Q701 headphones; put them on the dummy head; and measured the frequency response over time, playing pink noise in between measurements. I measured the cans fresh out of the box; immediately after the first test (so it had about 5 minutes on them); then after 25; then 1 hour; 2 hours; 5 hours; 10 hours; 20 hours; 40 hours; 65 hours; and finally after 90 hours of break-in.
Once all the data was gathered, I really couldn't tell what the differences where by eye, so I plotted the data as differences. I used the 90 hour data as the reference, and plotted how the data in each set was different than the 90 hour data. My assumption was that the first measurement out of the box would be most problematic, and that the data should settle in the direction of the longest burn-in time.
Any good mathematician will tell you that this method is a recipe for making the data look like it's settling toward the reference set. Just because the line in these graphs is getting less wiggly over time, doesn't mean that the frequency response is getting smoother. It just means that the frequency response is changing over time and moving in the direction of the 90 hour data. That's fine, because all I'm looking for here is a clear trend where the data changes smoothly from the start to the end reference, which might indicate a change in the sound over time possibly due to break-in. Whether it is break-in or not is another story. I just want to see if I could see trend in the data.
Let's take a look shall we?
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Comments
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.
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.
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! 
The data is stimulating, don't you think?
:)
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?
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.
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?
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.
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.
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.
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
Thanks for all the comments folks!
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!
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'.
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.
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.
I have a pair of headphones for dubstep, now I just need a pair for my classical music. [Paradox? You decide!]
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..... 
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 
? ) 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 )
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) ?
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. '
So I added a question mark.
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
"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.
does it account for pads wear-in over the longer time in the test ?
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?
If I don't win the AKG q701's, I'm gonna break-in somebody's face. I'm looking at you Bret Michaels.
great article Tyll!
The detail of your experiment is really great. My brain just exploded after reading this.
seriously.
hehe.
and I downloaded the spreadsheet to read on the train to my class tomorrow. it's gonna be fun!
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.
... 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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