I am not sure I am going to keep the cans yet. I cracked the headphone open for the first time last night and didn't find a whole lot of space to work with. My first order of attach, supposing that I will be keeping the headphone, is to apply violin lacquer to the inside of the cans which should alter the resonance property of the cheap plastic to something less plasticky and hopefully more organic sounding.
I did this with dacs before by applying the lacquer directly onto the circuit board and on their cheap abs housing, and the sound moved toward a smoother and less splashy midrange. I also rewired the dac which is something tempting to do with the Fostex, but I retired from soldering (lazy cuz I am not good at it).
That said, the phones do sound better now than when I first got them. I played it for 48 hrs straight. I received the v-moda cable today, so I am able to listen to the headphone out of my headphone amp and not just out of my preamp's headphone output, and I replaced the Audioengine D3 dac with the Audio Sector NOS USB dac.
MAYBE NOS dacs have better synergy with the Fostex. Whatever the case, the sound is much better today. Bass tones is weighty and sustaining. I still wouldn't keep the phones if this is as good as it gets though.
One more thing. I just noticed that if I lift part of the phones outwards to break the headphone cup's seal, the mid range becomes scary good like it's coming out of a compression horn speaker. Basically, if I don't do anything, the cups are angled like this \--/. And, by lifting the bottom of the cups a bit, the phones shoot straight into my ears like this |--|. I lose some lower bass this way, but mid bass kicks much more precisely and everything else is much clearer.
Another way of describing how I achieve this effect, press the top of the headphone against your head with your index and ring fingers. Then, lift the bottom of the headphone just slightly with your thumb outwards (away from your ears). Let me know if this works for you guys.
I am not sure how to mod the headphone to sustain this angle and openness though.
I just swapped ear pads between a DT990 pro and the Fostex T50rp. Both cans are sounding better than before. Or, it could just be psychological. One thing I hated most about DT990's bass is it's overwhelming close to distorting the rest of the FR. With the T50rp's pads, the DT990 sounds darker and there's less air. But, the bass is controlled, no longer "fat". Overall sound is more focused. I don't have measurement equipment, but I'd hazard to guess the FR is less V but emphasis is in the lower mids.
As for the T50rp using the DT990's pads, the sound is more open, more air. There's less bass but the bass is not more articulate, more acoustic. Overall, it's an improvement over the stock pads. However, with the stock pads and lifting the bottom with thumb, this "tweak" still sounds better.
Edited by viggen - 12/14/13 at 11:47pm