I was wrong about the ER-4 driver type. It's down to the variations in choice of driver descriptions, Etymotic describes the ER-4 as a dynamic system, while Westone uses that description for regular coneshaped drivers.
I will differ them as Westone does, since it's the terms i'm used to. So if i'm talking about dynamic again later, i mean a regular coned driver
Anyway, i haven't dived into the science of burn-in much, and if and how much influence it has. One thing has passed my mind though; most or maybe all of the posts and reviews i can remember to have read over the years almost always ends with either concluding that the sound doesn't change, or it's getting better. Has anyone experienced anything that gets worse..?
And what do you think the designers ment the product should sound like?
Should it be like the new design prototype they just finished, that measured the way they wanted and sounded like they hoped it would when they designed it, or should it be like the same new design hopefully will sound to them after a few months of use?
Just a thought..
You're talking about dynamic versus balanced armature burn-in, and why dynamic drivers does change more. From a technical point of view i'd just like to try make a suggestion of why it differs. I'm not trying to make or think i have the correct answer, i'm just giving my thoughts.
Just a simple (?!) description: A dynamic driver (the coned one
), as most of you probably know, consists of a stiff cone that's suspended over a magnet with a spider and a surround of some material as suspension, and it's coil floats inside the magnet. The spider is often made of fabric or plastic, and the surround are often made of soft plastic, rubber or foam. The thing burn-in would relate to is probably much down to how these suspensions are softened up more and more over time when used, just as your just-washed jeans are softening up when you have worn them a while.
In a balanced armature driver, there's also a (pretty flat) cone and a suspension, but the're is no free-floating coil. Instead, there is an u-shaped metal reed (some sort of spring-steel) called the armature, that's sits with one "leg" in between a pair of magnets. The reed is then connected to the speaker cone through a thin metal drive rod. (look at the picture)
To cut to the point, the current through the coil makes the upper leg of the armature to bend back and forth between the magnets and so pushes the cone. This means that the main moving part in the speaker is the metal armature leg, and since i guess metal wouldn't soften up over time as plastic, rubber etc does, it wouldn't change the speaker caracteristics over time.
And that was one more humble suggestion in trying to answer the big burn-in mystery..