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Is there scientific evidence that "Pink Noise"-Burn-In changes the sound?
Oct 5, 2010 at 5:29 PM Post #2 of 304
Here is a link to a post from a scientist: http://www.head-fi.org/forum/thread/471605/burn-in-experiment-proof/60#post_6392689
 
Oct 5, 2010 at 5:38 PM Post #3 of 304
Nice link.  Don't know how I missed that after so many threads on the matter.  Here's another post:
 
 
Originally Posted by IpodHappy 
 
As a physicist, I've spent a bit of time thinking about some of the factors which might impact audio performance of some of the IEMs.  Here are my thoughts relating materials science with what might be happening.  Please note that these hypotheses are not validated.
 
There are several changes which come from using your electronics:
1) With newer ceramic chip capacitors, there is some shifting of value under potential loading or aging due to instabilities in the dielectric materials.  These capacitors are also not linear with voltage.  I don't know what values are being used for current 2 or 3 driver cross overs or their body sizes, so I don't know if they are using the most recent dielectric materials.  Older electrolytic capacitors with polymer dielectrics also changed during forming, a process through which the dipoles would align with the electric field potential.
2) With sufficient time, even at room temperature, Cu, eutectic and Pb-free solders (SbAgCu or SAC) will anneal, changing their electrical characteristics slightly.  Plated Cu is especially susceptible (Cu traces on circuit boards).  Vacancies are driven to the grain boundary surfaces, resulting is slight shifts of resistance, but no more than would occur due to standard strains (Cu foils are often used as strain gauges since the Cu resistance will shift under strain).
3) If enough current is passed through the electrical conductors, the electron wind bombarding the atoms will result in movement of the conductor atoms, again largely along grain boundaries, in an effect called electromigration.  Hopefully, none of your electronics are designed so poorly as to experience this effect.
4) Epoxies rely on chemical bonding, called cross linking, during cure which results in densification and increased modulus (stiffening).  During the manufacture of products using epoxies, there is often a push to reduce production time by reducing the time allocated  for curing.  This means there may be additional curing occurring in the field.  How might this affect headphones?  In a dynamic driver, the voice coil is often glued to the diaphragm with epoxy.  As the epoxy continues to cure, the bond between the coil and diaphragm will strengthen, resulting in more energy transferred to the driver and less absorbed in viscoelastic deformation and internal friction.  This would likely result in better high frequency energy transfer between the coil and driver, improving high frequency efficiency.
5) The molecular chains in rolled or cast plastic films (driver diaphragms) tend to align to the rolling direction or surface on which they are cast.  This gives them a bit different modulus in plane compared to out of plane, and definitely impacts their coefficient of thermal expansion (CTE) in each of these orientations.  Vibrations during speaker use create micro fatigue in these molecular chains, resulting in slight re-arrangement of the molecules.  Usually, this results in a hardening of the material, caused work hardening.  I would expect this to be a second order effect compared to the continued cross linking which might occur over extended time periods as mentioned in (5), but again would improve high frequency efficiency.
6) In designs with metal speaker diaphragms (some BA drivers), the metal will also experience work hardening with cyclical stresses.  This would result in a slight hardening which would again tend to make the driver more efficient at reproducing high frequencies.
 
Just some thoughts.
 
 
I recommend searching prior threads on the matter since this topic gets out of control.
 
 
Oct 5, 2010 at 5:57 PM Post #4 of 304
Lately, burn-in threads have been tame in comparison to older threads. I guess people have decided not to take the subject too seriously.
 
Oct 5, 2010 at 6:06 PM Post #5 of 304
 
Quote:
rip n' burn said:
Lately, burn-in threads have been tame in comparison to older threads. I guess people have decided not to take the subject too seriously.
Click to expand...


+1
 
I think that has always been the issue. I do believe in burn in, but still take exception to "hourly" burn in reports.
 
What does running the headphones for XXX hours HURT before forming a lasting opinion of the headphones? Perhaps it is that the listener is getting used to the headphones, but I find I "shift" back to my old headphones very quickly even after a few weeks of listening to just 1 set. Nobody can demonstrate that drivers WEAR OUT due to normal usage, and you can run the headphones off of a small radio when your not listening... so why not? 
 
Another point on the whole burn in issue:
the face of head-fi is changing. The people who used to argue burn in (one way or the other) simply dont come here anymore. The people who frequent head-fi have fewer posts, and head-fi is not their "home forum" so to speak... the forum they check every day, first thing when they get back to work from lunch... etc.
 
Oct 6, 2010 at 4:52 PM Post #6 of 304
Quote:
Anaxilus said:
/img/forum/go_quote.gif
There are several changes which come from using your electronics:
Click to expand...
 
That may be, but the real question is whether such microscopic molecular changes are actually audible. I can see how a transducer can change audibly over time, such as the resonant frequency of a woofer as the edge material relaxes. But solder? That seems unlikely to be audible IMO.
 
--Ethan

 
Oct 6, 2010 at 5:02 PM Post #7 of 304


Quote:
ethanwiner said:
 
Click to expand...


I didn't post that originally btw so don't quote me personally.  I also don't know how you read that whole post and reply w/ solder doesn't change.  That's what you got from that?  Solder??
 
This is why it's not even worth talking about.  Not to mention it's been talked to death.
 
Oct 6, 2010 at 5:15 PM Post #8 of 304


Quote:
[...] the real question is whether such microscopic molecular changes are actually audible. I can see how a transducer can change audibly over time, such as the resonant frequency of a woofer as the edge material relaxes. But solder? That seems unlikely to be audible IMO.
Click to expand...


I think that the psychological component of this "burn in" business is far greater than any physical alteration to the equipment.
 
This is similar to my view on cable differences, which is that while there might be differences between cables the auto-suggestion involved in very much greater.
 
At present I have had a pair of AKG K702 headphones for about two weeks. I am "burning them in" by leaving them plugged into a radio overnight.
 
I just listen to them normally each day when I want to listen to music.
 
So, I remember on day 1 when I first listened to them without any "burn in" that they sounded awful.
 
Each day I listen to them, they sound better.
 
Surely a classic "burn in" story, the "golden ears" will say absolute proof of "burn in"!
 
But there is more...
 
Yesterday I went to listen to my AKG K702s when I wasn't really feeling like listening to music. I was just trying to work out something complicated to do with my current work and I thought it might be good to be away from my computer for a bit.
 
The headphones sounded awful again. In fact they sounded just like they did on day 1 without any burn in.
 
This time I was very conscious of this because it is, in fact, a long time since I bought something new for hi fi, I tend to get things second-hand.
 
I think new audio equipment sounds awful on day 1 primarily because you are discombobulated by it. The newness is a distraction from any decent listening. As you become more relaxed with the stuff you start to hear what it can actually do.
 
I would go further and suggest that maybe the reason why people say that the AKG K702s take a long time to "burn in" is that they are actually very good
smily_headphones1.gif
People just aren't used to hi fi that good at such a low price. They are initially discombobulated by it, however over time they start more and more to really see what happens with essentially neutral equipment.
 
Oct 6, 2010 at 6:35 PM Post #9 of 304


Quote:
p a t r i c k said:
I think that the psychological component of this "burn in" business is far greater than any physical alteration to the equipment.
 
This is similar to my view on cable differences, which is that while there might be differences between cables the auto-suggestion involved in very much greater.
 
At present I have had a pair of AKG K702 headphones for about two weeks. I am "burning them in" by leaving them plugged into a radio overnight.
 
I just listen to them normally each day when I want to listen to music.
 
So, I remember on day 1 when I first listened to them without any "burn in" that they sounded awful.
 
Each day I listen to them, they sound better.
 
Surely a classic "burn in" story, the "golden ears" will say absolute proof of "burn in"!
 
But there is more...
 
Yesterday I went to listen to my AKG K702s when I wasn't really feeling like listening to music. I was just trying to work out something complicated to do with my current work and I thought it might be good to be away from my computer for a bit.
 
The headphones sounded awful again. In fact they sounded just like they did on day 1 without any burn in.
 
This time I was very conscious of this because it is, in fact, a long time since I bought something new for hi fi, I tend to get things second-hand.
 
I think new audio equipment sounds awful on day 1 primarily because you are discombobulated by it. The newness is a distraction from any decent listening. As you become more relaxed with the stuff you start to hear what it can actually do.
 
I would go further and suggest that maybe the reason why people say that the AKG K702s take a long time to "burn in" is that they are actually very good
smily_headphones1.gif
People just aren't used to hi fi that good at such a low price. They are initially discombobulated by it, however over time they start more and more to really see what happens with essentially neutral equipment.
Click to expand...


Oh god, use the right thread please:
 
http://www.head-fi.org/forum/thread/505113/my-theory-as-to-why-headphones-appear-to-burn-in
 
 
 
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