That's the bit I don't get either. How do they actually compare when we know that our senses are limited to such a short time period of accurate auditory memory.
I don't discount there is something happening (especially after Tyll's tests on the K701) - but the thought that the differences are:
- audibly distinguishable after an x hour gap
- night and day (as some die hard burn-in believers state)
has me very puzzled to say the least.
I know that headphone position on the head/ears, and also pad changes (ie wear/compression) can make a very large and audible difference. So why is it that some people will swear by the concept of burn-in making the biggest changes, but discount the physical changes that we know actually do make a difference?
I just wish more people were open to questioning what could be happening (like Tyll's tests) - neither denying outright, nor accepting blindly - but actually searching for the actual reason for any sonic changes.
I don't personally discount any of physical changes that make an impact. Different ear pads, drive cups, cables can and will all have an audible impact. For me, what seems to happen on all my rigs is the sound becomes smoother. The rig will start out detailed but a little harsh. Over the course of time it seems to "settle down" and the sounds seems to morph into something a little more likening a caress. The notes are delivered with a more silky signature, rather than the harshness of the new kit. That's why to me there's such a difference which is easily memorable. If you just use the kit and let it burn in very gradually, say 2 hours a day of listening, it's going to take 6 months before you've reached 300 hours. If you just let it ride night and day whilst you're working and sleeping it will take around 15 days, so it's obviously far more noticeable if done that way.
With regard to adding other bits to the system, I now know what I like and what I've found to work. When ordering my last set of Grados I ordered wooden cups and HD414 pads at the same time. With those both present during the burn in process they can effectively be eliminated from the equation of what is changing the sound signal since they are there from the start.