[dfox]

In this case it might be exactly same as with chips, with headphones failing some QC test being labeled as cheaper and getting additional piece of foam to partially fix whatever badness was discovered in such test (like unintended resonance caused by manufacturing tolerances).

[varjag]

It most certainly isn't the same. It doesn't work like that with defective speakers.

[dfox]

In my opinion, the high-res photos in the original forum thread clearly shows some difference in build quality between both models. Compare for example how cleaner is hot gluing job on the driver on the 595 and that there is glob of something (hot glue?) on the external grill catch (lowest on first picture) on the 555 where there does not apear to be anything like that on the 595.

Extruding things from plastics (and especially ABS which this appears to be made from) is surprisingly inexact process and one would assume that manufacturing headphones selling for hundreds of dollars requires quite tight tolerances. My assumption is that the foam is there to damp rattling of case that is made from not exactly matched parts (and this is consistent with few posts in the forum which describe sound quality getting worse after removing the foam).

And I don't see why speakers/headphones/whatever can't be differentiated on quality, while having same overall design.

[varjag]

There is no way to sort out speaker driver rejects into 1st, 2nd and whatever category. If a sample has quality issue, it is likely to deteriorate further in use rapidly.

Lower quality speakers are not rejects of high quality speakers, they are just cheaper designs.

As to the mold, the holes there require no tolerances, they are there just to avoid air cushion behind the driver and serve no other purpose. Similarly, a foam pad is a rough hack to reduce its effectiveness, driving the speaker's response down. Do you really feel like this foam cut is some precision fix to tolerances problem?