Orthodynamic Roundup - Page 25

T20v2 damping-- Now with two helper discs!

Okay, so my little Panasonic LC33 couldn't capture the whole luminance range from the black Fostex baffle to the white of the vitamin bottle. Just cool it-- the poor thing's having self-esteem issues, sharing the shelf with newer cameras with better tone curves. Yes, that's right, photography can teach you about characteristic curves and transfer functions and that all-important linearity and when you don't want it.

But that's not important now. The T20v2 (that is, the second version of the venerable T20) is the Fostex headphone you're likely to see studio musicians wearing when they're not whispering intimately into their mics and leakage isn't a problem. Not that they leak very much. The vents are stingy, undamped, and don't line up with the driver-- it's more of a vented-closed-back than an open-back 'phone. The pads are big and very soft, so when you wear the phones the pads surround your ears like giant black marshmallows. It's a quasi-circumaural, like the original T20, but with poofy pads.

Inside there's the same Fostex driver clamp that we first saw in the original T20 and that lets you take the driver to pieces if you like-- no need for that, though. Disposable fake chamois is a paper product denser than the cheapo fabric-store felt, and I chose it based on what the stock T20v2 sounded like; it basically comes from the factory with the same mod I gave the T40v1 mentioned earlier (viz., there's a big fat cylinder of foam jammed between the back of the earcup and the driver) and yet it was still dull, heavy and midrangey on top of that, though I could hear a very healthy bass underneath. So I figured a lot of damping would be the answer. So in the photo you see the orange dollar-store fake-chamois stuff, cut to fit using the bottom of the small Welby vitamin bottle from Aldi. If you have to resort to measuring, the diameter of the damping pad you want is 37mm. This at first simply sat on top of the factory white nonwoven damping film, which is (unlike the T40's) glued firmly to the driver's rear magnet. Silly me, I figured this would do it.

And it mostly does. Put the 'phones back together as you see them in the photo and many of you would happily listen to your favorite techno and electronica to follow the bass lines-- the little driver basses very well indeed, and the bass is speakerlike, extended, and tight. The midrange was tamed and the whole presentation was reasonably close to flat. But the top end, the top two octaves, was weak.

Okay, we could use a reflex disc, and I tried that, but the bass got a little dry. Remember, a reflex disc used the normal way (same diameter as the damping disc) makes whatever damping pad you're using damp harder, and this is especially true in the case of the T20 and T40, where the driver clamps put both damper and reflex discs in a shallow recess, giving the backwave no way out if both discs are the same size. No wonder the bass dried up-- the driver had been effectively sealed. Whoops.

So I did something I mentioned awhile back but never tried til now, and that was to use a small reflex disc the size of a US quarter (24mm) to give the backwave a way to escape and so not wreck the bass. The extra bit of damping helped: bass tightened up, the midrange calmed down, and the highs started to come up, but they were still weak, since the denser damping pad was letting fewer highs through for the reflex disc to reflect. We were close, but we'd hit the limits of what damping and normal reflex-discery could do.



BEHOLD THE REFLEX DOT

So I stuck a small self-adhesive 3/4" (18mm actual) paper dot from the office supply store...



...under the sham chamois, right on the driver's white damping film. There aren't any magnet holes in the middle of the T20 driver, so I offset the dot so that it was behind the maximum number of holes, then lay the damping pad and its 24mm reflex disc (now functioning more to tune the damping than anything else) over it. Putting this reflex dot directly (or in this case almost directly) on the driver gives a very strong treble reflection, so it doesn't need to be big. The advantage is that the reflex dot placed ahead of the damping pad doesn't affect the damping, so no overdamping problem. To be fair, a reflex disc less than, say, half the diameter of the damping disc would have a minor effect on damping no matter where you put it.

For ease in tuning the highs on your T20v2 to your own exacting specifications, try several even smaller dots, just bigger than the magnet holes.



Again, the sequence goes like this:

0) driver itself

1) driver's white factory damping film (maybe we should call these "diapers")

2) 18mm sticky reflex dot, offset to offer a reflective surface to the maximum number of holes. Adjust diameter (and thus the level of ~the top octave) to taste.

3) 37mm disc of fake chamois, the main damping pad (this is the only bit on this list that's visible in the top photo)

4) 24mm damping tuner. Adjust diameter to even up the bass and avoid midrange honk. Use tiny bits of sticky tape to hold it in place during reassembly.

5) factory foam puck to hold it all firmly against the driver


Make sure the wiring is out of way when you reassemble. Don't let the cable get between the foam puck and the driver. Fostex thoughtfully provided little posts to jam the cable against to dress it out of the way.

The T20v2 now has "statty" highs like the modded T40 plus extra efficiency and more bass. There's a little hump in the midrange, but it's smooth and many of you would like it since it accents female voices just a touch. It's an impressive change from stock, and there was only paper involved, no soldering, not even felt (unless you want max bass and want to damp the vents). Keep in mind that this isn't a final-final mod, just a suggestion to get you in the ballpark. Frankly, I think the driver needs a little more damping than even the fake chamois can provide, so maybe it's back to the fabric store for some ultradense felt. Another good idea would be to fill the empty earcup space with something that absorbs sound, like fiberglass or bonded Dacron fiberfill [EDIT: Dacron fill was tried later by scompton and found to have a minor effect at best]. But the mod laid out above will get you 90% of the way there.

Now, the interesting thing is how differently the T20v2 and T40v1 react. The 'phones sounded roughly similar stock. Modded, the T40 is electrostaticky and about 6dB less efficient than the T20, even after the T20's been modded. And the two drivers must've been factory-tuned differently, because the T20's bass came up beautifully and the T40's retreated to "pleasantly AKG" or "improved Lambda" level.

So, surprisingly, the T20v2 is the one with room to try different mods. Fortunately for the T40v1, the mod described above in post 337, which is the simplest mod possible (not quite, as I erroneously stated earlier, the only mod possible, but rather one of a limited number), makes the phones sound great; the T20v2, on the other hand, could be a bass monster or a tight, SRX-style detail maven. Next I'mna try the T40 earpads on the T20. [UPDATE: my advice: I didn't like it, but don't let that stop you from trying it-- it's an education in sound shaping]

And here I thought the T20 and T40 drivers were more or less the same. Tsk.
Ah, well.

Anyway, jump in, the Fostex are lovely and warm. And you were going to the dollar store to pick up an LED nightlight anyway, weren't you?


PS: swt61, great job. Look at how far that bass backwave will have to go to curl around and chew on the earpads. Let me know if you get any feeling of openness (do the open-palm test).

UPDATE: Here's Faust2D's mod, which looks promising: http://www.head-fi.org/forums/4166901-post2410.html