Today some interesting and surprising measurements.
after 5 hrs of 'burn in':
There seems to be about 0.5dB more 'bass' which seems unlikely to be very audible. NO changes to speak off above 90Hz. It should be noted that the ambient temperature in the room had increased a few degrees and the EVO had been playing VERY loud for 5 hrs continuous and was measured directly after the music stopped.
I say.... no really obvious changes in FR that warrant a sonic signature change.
Next question.... what does the felt do.
My hunch was the differences between old and new were solely due to the felt and so do some report.
Hmmm little change.... only a few dB extra from 5kHz to 10kHz and around 15kHz about + 8dB.
The 'air' is somewhere between 13kHz and 20kHz so indeed removing the felt ads 'air' and those brushes become more realistic as do cymbals e.t.c.
Not much extra highs but a few dB is audible.
b.t.w.... I couldn't believe that thick felt didn't do that much so remeasured it 3 more times.
Dip at 4kHz is still there.
How does the old HD681 (stock) compare to the HD681-EVO WITHOUT the felt:
Hmm can definitely say these do NOT sound the same once the felt has been removed.
I would even dare to say... they changed the drivers !
This isn't that far fetched as all the Superlux drivers LOOK exactly the same for the other models as well yet sound and measure different.
pads that may give a clue.... grabbed some old HD681 pads which differ in thickness, finish and appear to feel slightly softer.
below stock pads versus old HD681 pads:
Some differences in the lows (as expected they are different in height) but from 1k to 10k little different. Above 10k could also be different because of a slightly different position on the rig or the pads differ..
Time to play with pads...
Played with various different pads and DT990 was promising (very flat from 20Hz to 5kHz and a slight raise for the highs, lows were a tad below flat so it sounded a bit 'boring' and nothing like the original. The 990 pads are smaller so cannot be properly mounted either.
SRH840/940 pads weren't that different from the original pads so 940 pads could be a good option if you like the signature but want velours pads.
I have some T50RP pads lying around for some reason
and as they are the correct size I fitted them.
Since they are much thinner I hoped for slightly less lows.
Below the difference between EVO and T50RP pads...
Drivers are closer to the ear though. A difference between original and EVO is the baffle as well where the driver of the EVO protrudes and in the original it doesn't. Pads of EVO are thicker as well though.
Bass had the same level but everything (mids to highs) above it is 'louder' which basically means there is less bass with the T50 pads.
It should be noted that both measurements are without felt.
So below Stock HD681-EVO (left+ right) as you can see the driver matching is EXCELLENT.
Now compare to EVO without felt and with T50RP pads.
I think this is what I was looking for.
I do not feel the need to reduce the bass even more and it sound wonderful as it is now.
NO need for electronic filters... just rip off that felt and try to get some T50RP pads...
For those with protruding ears that hate it when their ears touch something these pads may not be the best idea.
No problems with my ears.
The biggest issue I have with this headphone (aside from the shiny plastic) is the
MICROPHONY of that cable.
Sound wise, however, it is quite pleasant and close to a filtered old HD681.
I will still research what can be done with K240 pads and maybe some filtering but this preliminary result satisfied my dodgy old ears.