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Headphone Burn-in...Part II - Page 2

post #16 of 26
Quote:
Originally Posted by Tyll Hertsens View Post


I just might do the earpad replacement measurement.  I've got an old pair of 600s with mushy pads to use. Good idea.

 

662 hours is is almost a month. I just can't tie up my chamber for that long when there are so many headphones to measure. A perfect example of why I really can't do research. 

 

Thanks for the comments!

 



I totally understand on the time thing - especially when half of that time the headphone is just sitting there, waiting to be measured again.  I know you say you can't do research, but you've already done better than anyone can do short of the biggest audio companies and major research universities.  It's excellent groundwork from which bigger studies could be developed, which is a big achievement in and of itself.

 

As for the 600 pads - I'm glad you like the idea; it'd be great to see what that results in.  I was thinking about the different Grado pads, too, but figured that someone had measured them - you of course!  I noticed that the link to the PDF for those tests is broken though: http://www.innerfidelity.com/images/Grado%20Headphones%20And%20Ear%20Pad%20Tests.pdf

 

Actually, the Grado pads switcharoo thing reminds me of the most popular HD 600 mod - taking out the foam clamped underneath the ear pad.  That'd be something to consider doing too if you do in fact put the 600s on the test rig.  Not quite related to the burn-in phenomenon, but interesting nonetheless.

post #17 of 26

Tyll - Thanks for getting back to me, interesting.  I hadn't thought about seismic issues as well, so many variables...

 

arnaud - Saw some regularity to the jumps, but didn't realize it was consistent.  Like you said, weird.

post #18 of 26

Posted on inner-fidelity website in the comments section: Thanks for the clarification on the experiment Tyll. The sudden jumps are quite puzzling and I still can't imagine they're related to the excitation signal. One thing that came back to my mind is that the input signal is (fortunately) taken out of the equation when measuring the impulse response by MLS. The impulse response is obtained from cross-correlation between the input signal into the amp or heaphone and that of the microphone.

So, as long as some noise is injected over the audio range, you'll get the same frequency response function (assuming the system measured doesn't change) even if the input signal varies a bit in level and other frequency characteristics.
The puzzling part is that the jumps don't occur at fixed interval (every 50 hour +/-15 hours) but they all do the same thing (increase level by up to 2dB, the higher the frequency, the more visible it is). Another puzzling bit is it would appear all the responses after the jump are similar, so it's like resetting the response to about what it was at the last jump...
 
The one thing that makes sense is that the variations are more pronounced at high frequencies since it's where the response is most sensitive to slight perturbations in the system.
 
You know your test rig better than anyone, but I wonder if you could get more representative results by performing standard 5 position average tests every 50hours of burn-in or so and compare that against another pair of same headphone which would also be measured every 50 hours but not being used in between tests.
With such test, you would not only address the question on measurability of burnin effects but you would also show if any variation observed can be just as much attributed to burnin as simply natural uncertainty in the measurements (temperature, spurious noise and vibration, ....). BTW, you also wouldn't have to monopolize the test rig for the whole duration of the experiment in that scenario and you could make sure you control some of the environment variables (temperature, exterior noise/vibration...).
 
Considering some people often try to dismiss measurements when a headphone is objectively criticised or large variations are observed between several pairs of the same model, addressing the level of uncertainty in the measurement would be extremely useful to do (not just for the fun of it but simply to give more authority to the results presented on this site).
 
End of long rumbling post ;)
post #19 of 26
Quote:

Originally Posted by arnaud View Post

 

I wonder if you could get more representative results by performing standard 5 position average tests every 50hours of burn-in or so and compare that against another pair of same headphone which would also be measured every 50 hours but not being used in between tests.



If you go that route, you do get confusion of sample variation added into the mix. Sure you would have a baseline measurement to know where the differences were, but it would muddy the comparison, certainly. 

post #20 of 26

^^

actually, not aiming to compare the 2 headphones. Would look at one (no burnin) to verify natural uncertainty in tests, and would look at the other headphone to see potential evolution over the burnin period.

 

As far as samples variation, it seems to depend on the headphone. An example for sr009 and lcd3: http://www.head-fi.org/t/575751/new-audeze-lcd3/3060#post_8039705

post #21 of 26
Quote:
Originally Posted by MacedonianHero View Post

I didn't realize my posts wielded so much power? wink.gif I'll try to be more careful in the future. tongue.gif

 


After reading your post I woke up in a roadside ditch.

 

 

 

post #22 of 26

Did the headphones sound grainy in the first few hours ?  I thought mine sounded a bit grainy straight out of the box.  

post #23 of 26

I know in the laser world that a temperature cycle from -5 C up to 60 C will generally adhere the critical optic bearing o-rings to the mounting surface making the laser more reliable.  Perhaps what we all think as "burn in" is really a measure of how many temp cycles the unit has gone through.  It would explain why so far the measurements Tyll has made has not revealed major changes over +/- 2dB.  Everyone has noticed the changes due to the hot / cold cycle which I find far more drastic than the long term burn in measurements.  I still think that some sort of burn in exists and each headphone and how it was constructed is different.  To say that the headphones do not change over time at all is ridiculous.  That is like saying things do not age or break.

 

Having more data to back up a hypothesis is always a great thing and those of us in the science community need to remember that a hypothesis without support or rigorous testing is merely that...a hypothesis.

 

In regards to the first tests we did with the AKG-Q701 sets of headphones it is pretty clear to me that both the green pair and white had different sound signatures and we provided very little if any evidence that this was from burn in.  As someone mentioned earlier it could have simply been driver differences or how each pair was constructed.  Now if the burned in pair of headphones from say 100+ tests always sounds smoother that is another matter.

 

Here is to following the scientific method whether it proves or disproves a hypothesis.

post #24 of 26
Quote:
Originally Posted by NA Blur View Post

I know in the laser world that a temperature cycle from -5 C up to 60 C will generally adhere the critical optic bearing o-rings to the mounting surface making the laser more reliable.  Perhaps what we all think as "burn in" is really a measure of how many temp cycles the unit has gone through.  It would explain why so far the measurements Tyll has made has not revealed major changes over +/- 2dB.  Everyone has noticed the changes due to the hot / cold cycle which I find far more drastic than the long term burn in measurements.  I still think that some sort of burn in exists and each headphone and how it was constructed is different.  To say that the headphones do not change over time at all is ridiculous.  That is like saying things do not age or break.

 

Having more data to back up a hypothesis is always a great thing and those of us in the science community need to remember that a hypothesis without support or rigorous testing is merely that...a hypothesis.

 

In regards to the first tests we did with the AKG-Q701 sets of headphones it is pretty clear to me that both the green pair and white had different sound signatures and we provided very little if any evidence that this was from burn in.  As someone mentioned earlier it could have simply been driver differences or how each pair was constructed.  Now if the burned in pair of headphones from say 100+ tests always sounds smoother that is another matter.

 

Here is to following the scientific method whether it proves or disproves a hypothesis.


It sounds like what is happening with the optic bearing o-rings in the lasers is that the the cycle up in temperature means the o-ring is just better seating itself with expansion.

 

The o-ring (probably made of Buna synthetic rubber or Viton) has a much higher coefficient of thermal expansion than the metal the o-ring groove and face are made of.  This means that when you cycle up the heat like that, you're expanding the o-ring more than the surrounding metal, and as a result of that expansion it will center itself, ensuring equal pressure on each side.

 

[I design pump ends, and we never even consider this - for more common applications the standards are there so we don't have to.  Our pump ends, which see pressures of up to 300 psi or so, use typical o-rings, and never see high temperatures.  It'll be months before a pump made in the winter sees anything more than 70 F or so unless it's cavitating, and o-rings are rarely the cause of leaks, at least during production.  Interestingly enough, manilla (like the folders) is the most common material for gaskets!]

 

I'm not sure that such an effect is even applicable to transducers - there's no interface like that.  I'm not sure that temperatures that high are normal conditions for a headphone - perhaps right around the coil under very high load, but that's all as stiff as possible (and designed for expected max heat) anyway.  The compliant part of the driver never gets hot.


Edited by BlackbeardBen - 1/25/12 at 10:49pm
post #25 of 26

I just spent an hour listening to and comparing a used pair and a completely new pair of HD650's.

 

I did a blind test with a friend and neither of us could tell which was which. 

 

Either our ears are very bad or there simply aren't any differences that we could possibly have noticed. 

 

EDIT: Actually, I noticed a difference. The used pair was a lot mot comfortable. :)


Edited by davidgotsa - 1/26/12 at 9:55am
post #26 of 26
Quote:
Originally Posted by davidgotsa View Post

I just spent an hour listening to and comparing a used pair and a completely new pair of HD650's.

 

I did a blind test with a friend and neither of us could tell which was which. 

 

Either our ears are very bad or there simply aren't any differences that we could possibly have noticed. 

 

EDIT: Actually, I noticed a difference. The used pair was a lot mot comfortable. :)


Actually, that militates for Sennheiser. That the pads change is inevitable but the drivers shouldn't "deteriorate" as much to cause noticeable changes.


Edited by xnor - 1/26/12 at 10:35am
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