We've opened the ATH-2 and Technics EAH-830 preparatory to installing some damping materials, but mostly just to gawk at the internals. There were more variations on the isodynamic headphone driver theme than I imagined, but as I've said elsewhere, I'm not the expert; I'm just on a voyage of discovery. What separates me from the dilettante diddler is, I pronounce
voyage as voy-YAWGE,
Thurston Howell style. Which, I think you'll agree, makes all the difference.
But that's not important now. We want to look inside the 'phone that was the first major step up in the original 1978 Fostex line, the T30. The sound we've been getting from it is nice, in that with some bass boost the thing has a low end that must be heard to be believed, but the treble kinda dribbles away. Don't get me wrong-- it's smooth, so if we EQ'd it with a multiadjustable EQ unit, like a parametric, we could bring the top end up and it would be reasonably flat.
Still, we've gotten good treble out of the more primitive Yamaha Orthodynamics by damping them, and the next Fostex step up, the T50, has a very extended treble, so we should be able to extract a decent top end from the T30, which has a similar serpentine diaphragm. What's so good about a serpentine diaphragm? It's pretty, for one thing...
..and Fostex has always claimed that it's better behaved than a spiral voice coil diaphragm, such as is used in its own T20. It certainly looks harder to make. I hope you can see the very fine aluminum traces on your monitor. A thing of beauty, I think you'll agree. The T30's driver differs in other ways from the one in the T20, starting with size. It's about 60mm across versus 45. The T30's magnets are stronger than the ones in the Technics; you have to hold them with both hands to screw the clamp down. There's no nodal clamp or damping button or whatever that thing in the Technics is, so that big diaphragm is free to
move, baby. The magnets are the usual [ferrite?] discs, but instead of holes there are slots aligned with the M-shaped voice coil traces. See that translucent goo around the perimeter of the magnet? That's silicone grease. The diaphragm is held in a greased clamp. I think the idea here is to help absorb surface waves as they travel toward the edge of the diaphragm so they're not reflected, and also to let the diaphragm stretch a little during big excursions. It's an interesting detail, that's for sure.
And it turns out that the only damping was one of those fluffy fiberglass-looking biscuits stuck to the back of the driver. I think some felt will work wonders here, as it has for the Yamas. We'll have to continue this later, but I have restrainedly high hopes. Stay tuned.