Tyll did a similarish test with similar results. Also with Q701
test1,
test 2,
test 3,
test4
Rtings also tested some other headphones which makes the test more interesting because there is a larger sample size over different brands/types.
I tested this as well with a cheap Superlux HD681EVO.
The reason for that was I modified many HD681 (not EVO) and in 2 of them I found the bass to be lacking while the other ones were bass monsters (no test rig in those days yet so anecdotal and subjective).
These were 15 Euro headphones.
I could directly compare them with other ones which helps.
In one of them you could hear the bass level improving during one song.
The other one had very little bass and may have improved slightly even after blasting it for hours.
So when 2 of them came in for testing (first production run) I set one aside and tested the other.
The other one was put on the rig measured directly and left on the rig.
Blasted with very very loud music (till I could hear it distort on the outside).
After about 8 hours measured it again.
May have warmed up slightly during the day and had quite a lot of power on it.
first measurement,
after 8 hours.
Compared it with the other one and sounded the same.
Indeed my opinion is that pads tend to compress more over time/usage which changes the tonal balance.
New pads are generally much stiffer than older ones.
Below HD58X with
standard pressure and with the
pads compressed a little.