"Driver flex pop," as you call it, is not what I am referring to. I am referring to the actual diaphragm of the driver being pushed out of its proper alignment during insertion into the ear canal or as a result of movement inside the ear canal during extended use. During the course of my review, there were several points where I felt the Advar had less bass than it did when I first started listening to it. I confirmed this with measurements that showed that the Advar had basically neutral bass in this state. I had to pop the diaphragm back into alignment by pushing the housings as deeply into my ear as possible with the largest tips I had to get the intended levels of bass back.
As I stated in my review, this is not the first IEM I have had this issue with. The same thing happened with the Dunu Luna, and I had to perform the same procedure to get it to sound like it ought to again. The issue seems to be that to get a very high-performance dynamic driver, you have to make the diaphragm as thin as possible, but it is so flexible that the pressure of insertion into the ear canal can move the diaphragm out of alignment, compromising the tuning. I don't see this as a QC issue as much as a design compromise. This is not an issue of seal in the traditional sense. As a matter of fact, it may be an issue of too much seal in terms of the size and grippiness of the included eartips.
