preliminary results: T50RP results, T20v2 preliminary results
Removing all damping from the T50RP driver and letting it operate in its vented cup (with the little hole sealed) theoretically gives us the most bass this driver is ever going to give us, and it's adequate at best. After hearing good iso bass from the Pro 30 (the standard for this comparison, using the Panasonic SA-XR10's digital amps), the T50RP lops off the bottom two octaves [EDIT:and it was a true lop, the result, it later turned out, not of too much diaphragm tension as I had originally thought, but of earpads that let bass leak out and bass backwave leak in] . In this state, the T50 suggests bass very nicely, and if it wasn't for the big hump in the upper midrange, it'd be acceptable. Damping out the upper mid hump with a layer of felt gives a peaky sort of treble and moves bass cutoff an octave or so higher, which removes all suggestion of bass. Fooey. [EDIT: Not to worry-- the improved earpads that came along sometime during 2007 changed the prospects of this headphone so completely as to remake it, but since it's just an earpad mod, we continue to call it T50RP.]
The T20v2 from Tyre has these big poofy comfy cushions that make it grinningly comfortable. Bass is okay, but there's some of that midrange rise (= honk), and there's no high treble-- just the opposite of what Tyre likes, the AKG sound exemplified by the K240 Sextett (or the surprisingly similar K501).
Since there's some bass to work with here, a reflex disc and a thin damping pad might just tame the midhonk, goose (heh) the treble and save most if not all of the bass. Will it ever be a HF darling? Probably not, but with some EQ you'd have the tight bass and treble sparkle of a good iso. [but see link below] Trouble is, even though they're not expensive even when new, the rugged contruction makes them heavy and bulky, and they are expensive compared to the bang for the buck you get from the Pro 30. The T20v2 shows that, alone among the early makers of isodynamics, Fostex really did know what they were doing. It's just that with the exception of the T50 (and with reservations the T30), what they were doing was stuff that HFers wouldn't get too excited about. Not surprising, since pro sound is almost never purist/audiophile sound, often by emphatic intent.
I hope to be able to change that for the better.
To sum up, the stock T20v2 sound is very like what I heard from the T20v1, only louder, because the magnets have been improved. There's a bit more [good] bass with the T20v2. Damping the T20v1 with a felt disc and a reflex disc gives good mids and a crisp treble, but the bass is gone. [UPDATE: This was due to a peculiarity of the T20 and T40 drivers: because of the driver clamp, the driver and any felt damper disc you use sit in a shallow recess-- the same-size reflex disc thus effectively sealed off the rear of the driver, and that's guaranteed to kill the bass on anything. See the later experiments, which were much more successful.]
Edited by wualta - 12/5/11 at 10:07am