EDIT - I have a second theory on post 166, because of the following discussion (which can get very lively and has a lot of dross in it) and evidence found.
Here is why I think that the audiophile idea of headphone burn in, as in it is attributable to the headphone is nonsense and the actual reason as to why it appears to happen.
I have been collecting vintage headphones and overall I have 13 headphones, new and old. I tend to listen to one for a few days and then switch. I recently got a loan of so IEMs to try for the first time. I did not really take to them due to the lack of soundstage, comfort and lack of bass and treble. I was complementary about it sound, but thought that when I go back to my AKG K280 Parabolic full sized around ear four diver headphones, which I had been using prior to getting the IEMs, the K280s would sound spectacular. But they didn’t for a day or so. Then they did. They returned to their spectacular sound.
Thinking back to various headphones and their supposed burn in, there are too many inconsistencies for there to be actual burn in. Some examples;
AKG K702. Supposedly needs hundreds if not thousands of hours burn in. But they are very detailed and make little background noises easier to hear. If you are not used to such detail then as you listen to music over the year, particularly albums you only listen to occasionally, you will keep noticing little details you have maybe not been able to hear before. That is then attributed to the headphone, but it is not, it is you hearing something for the first time.
Sony DR4C. The 10,000 ohm headphone. Very difficult to drive and it took me a while to set the amp right for these to sound at their best. They are from the late 1970s and so are run in in as much as any minor mechanical changes to the driver have happened. But they got better as I got used to using them.
The AKG K280 Parabolic. As I said above I loved these from the start. I then tried IEMs which overall, I did not like as much. But when I went back to the K280s, because the change was so extreme, it took me a while to get used to them again. They have not changed, it was me.
Grado SR80s. They often sound a bit too bright at first, but quickly get to their dynamic attacking best. Moving on to something else afterwards can make that headphone sound dull.
AKG K44. Bought new my baby, cheapest cans, but remarkable in that I am always used to their sound and it has does not change one iota moving from one headphone to another or over a period of listening.
Sony DR5. They have always sounded bright and a bit thin. They were sold as hardly used, so may not have run in. But they sound unchanged in the time I have had them.
AKG K140. Vintage and going by marks they are well used. No change with them, but like the Sony DR4C they needed getting used to and sound a bit flat when I move to them from something more dynamic and bright.
All of the above changes are caused by me and my ears. The idea of burn in attributable to the headphones is not consistent and can be explained by changing from one headphone to another, or just getting used to each headphones sound; its dynamics, and particularly detail.
That is my reason why burn in does not happen as some audiophiles claim it does. All posts which say ‘that headphone needs burn in’ should actually read ‘that headphone needs getting used to’ or ‘that headphone does not suit your hearing, you can either try and get used to it, or get another pair.’
Edited by Prog Rock Man - 8/29/10 at 3:18am