More DIY Orthos, and Two AKG K 340

More modified headphones came through the lab this week. scompton sent in three modified Fostex Orthodynamic cans, and Morphsci sent in a couple of modified AKG K340 headphones.

Quick pix, and impressions follow!

Fostex T40RP

scompton notes - The T40 has craft felt on the back of the driver. I experimented with different materials to hold the felt to the driver. One cup has aquarium filter foam and the other is stuffed with fiber fill. I couldn't hear a difference, so I left them like that. I am curious to see if they measure different. I've also removed the foam ring from the baffle because it irritated my ears. That's the only irreversible mod I've done.

Tyll notes - Wow, the pads have degraded in an interesting way. Looks like my grandma's forearms. Sound is somewhat thin and lacking in the lows. Has a fast edgy sound up top, but highs are distinctly articulated. Overall sound is coherent, but I can't really get past the missing lows and zip up top.

I didn't hear any difference between the drivers; measurements show a slight difference. Headphone has polarity reversed.

Click on graphs image to download .pdf for closer inspection.

Fostex T30RP

scompton notes - The T30 has a reflex dot and heavy felt on the back of the driver. Aquarium filter foam holds the felt to the driver. I also switched the stock pads with Sony XB700 pads. The stock pads are thin leather. Since there is no swivel to the ear cups and they are parallel, they are extremely uncomfortable. The XB700 pads solve this. Before changing the pads, these only came out of storage for meets. They were just to uncomfortable to use for more than 5 minutes. With the XB700 pads, they're my favorite headphones

I just thought to add that the T30 is a pretty rare headphone. Only a handful of people on head-fi own them and in the 5 or so years that I've been looking, mine is the only one I've seen on eBay. Someone else found a lot of 3 on eBay that I missed and a few other people have found them elsewhere. Many of them should exist because they were made by Fostex for a while.

Tyll notes - The Sony XB700 earpads are plush, comfy, and sound better here than on their original headphone. These sound quite good. Nice big, tight bass on these cans; nice transition from bass to mids. Highs can be a tad zazzy and accentuated over the mids, making them sound somehow slightly distant. Overall quite good though.

With exception of something weird happening on the left channel THD between 1-2kHz, the measurements are excellent. Nice fairly flat and long top on the 30Hz square wave indicating very good bass response. Front edge of the 300Hz square wave shows some ringing but little overshoot. Impulse response is quick and in polarity; it has quite a bit of energy in it's ring, but damps nicely after that with little noise.

Click on graphs image to download .pdf for closer inspection.

Fostex T20RP

scompton notes - The T20 has dense wool felt behind the driver and in the back of the cup, held in place with aquarium filter foam.

Tyll notes - This headphone, it seems to me, has a very typical vintage Ortho sound: A mid-centric headphone with very nice rendering of voices; a bass that doesn't quite come up to the level needed to pair with the mids, but has good tightness and extension; and a treble that's somewhat rolled-off with a bit of an edge to it.

I think this is the largest supra-aural pad I've ever seen.

Measurements are good for a typical mid-centric headphone. Good grouping of raw frequency response data shows that large pad is sealing consistently the same, and well enough for good bass extension. Blip on rising edge of 300Hz square wave indicates some harshness, which was heard; shape and damping otherwise looks good.

Click on graphs image to download .pdf for closer inspection.

Now, on to some very unusual electrostatic/dynamic headphones ...


inarc's picture

Thanks for the measurements; I had always been curious about the AKG K340.

morphsci's picture

I'm glad to be able to see some measurements. They do require a bit of power and they are definitely not for everyone (maybe just Me and Philodox).

makiem's picture

WOW... 2 AKG K340.? seriously?