[RedLeader]

I've been bugging a buddy of mine about his jensen cans for a couple months ago, and he decided to get a pair of senn eh150. Wasn't my recommendation, but they're alot better than what he had. He was looking through his dads old stuff, and came across an old pair of cans. Knowing that I'm an electronics and audio nut, he offered to let me borrow them. He said they were fostex. Having never heard of the brand I looked around for them, and found their site . There wasn't any information on the older ones I had, but of course I couldn't wait to listen. I had to resolder some internal connections and do some fixup (They ARE 15 years old after all) and as I was doing so, I decided to take apart the cups and look at the driver, I found this:

2 magnets, with a coil inside! Here's a closeup

This is some of the information I gathered "The T40RP utilizes a newly designed d ‘RP Diaphragm’. This unique Fostex technology employs a copper foil-etched polyimide film to provide resistance to high level input peaks of up to 3000mW combined with a neodynium magnet for high sensitivity and excellent transient handling."

Very cool indeed. Here are a few more pics, read afterward for my impressions. Keep in mind that I am not incredibly experienced in the land of heaphone audio, this is just what I can hear.

With a KSC-75

Now onto what I thought of these unique cans. My test rig was both a D-141, and a Revolution 5.1. CDs and FLAC respectively. They are quite comfortable on the head, even if they are a tad weighty. The isolation is slightly better than my HD201, which is to say not great, but more than enough for my needs.
The first thing I noticed was the seperation of the soundstage. Being more used to the closeness of my daily portables the 75s, I was pleasantly surprised. On Imogen Heaps track Hide and Seek, I loved them. They do justice to her voice. This track has no bass to speak of, and I love these cans on that track. I found the mids emphasised, compared to my normal colored cans.
Moving on to Audioslave - Out Of Exile, I heard the highs come back. Where they seemed slightly recessed, they were now nice and bright, a good balance, if still slightly overshadowed by our friend the mids. The bass reminded me alot of philodoxs K340s from the last meet. The bass is all there, it just isn't punchy enough for me.
I moved to SOAD - TCMMFLIOTS. It opens up with a very punchy guitar/bass drum riff, and I felt that it didn't quite do it justice. Compared to MS-1, it was very laid back. The responsiveness seemed to be there, but it wasn't as in my face as I like. With SOAD I like to crank it, and I decided to test the claims from the Fostex website that they can be cranked without distortion. I decided to put my ears on the line, and I hit 100% for a few seconds. NO distortion that I could percieve, on SOAD - Chop Suey, and Tool - Parabola. Quite good indeed. I did however notice a very nice increase in the bass, compared to the rest of the frequencies. I do not have my home amp done, so I could unfortunately not test these cans with enough power, but I have a feeling that when given that boost, they will indeed satisfy my love of deep bass. With Tool - Ticks and Leeches, I was extremely impressed with the opening drum solo. They responded quickly, and with the new volume levels the bass impact was where I wanted it to be.
Moved onto Black Eyed Peas - Don't Phunk with My Heart. At the end of the song there is an extended period of deep impact thumping. They responded wonderfully, very clean, crisp and accurate. Meanwhile maintaining the womans voice quite well.
I moved onto Buddy Rich - Dancing Men. These are my new favourite jazz cans. I can seperate the instruments out, and the drums sound great. No sibilance or distortion from the cymbals, even when cranked. The trumpets sound rich and full, and everything mixes quite well.

The claim is made that these are if anything balanced cans, and I would definetly have to agree. The highs are bright without being harsh, the mids are there without being overpowering, and given enough juice the bass is extended well, and full enough for everyone but a bass-head. Needless to say, my friend will not be getting these back anytime soon. If anyone would care to explain precisely how these function, I would appreciate it.

 

[kramer5150]

Cool... I see those on ebay for $25-$75...
**edit**... Its the T40RP I see on ebay al lthe time. THAT one (T40), I've never seen before.... wow Rare bird!!

John Petrucci's can of choice.

 

[catscratch]

http://headwize.com/articles/hguide_art.htm

Quote:

The transducers in isodynamic headphones are miniature versions of magnetic planar loudspeakers. They have thin diaphragms into which a flat voice coil is embedded - like a printed circuit - for even distribution of the drive force. Magnetic assemblies on both sides of the diaphragm supply the magnetic field in which the diaphragm vibrates. Isodynamic diaphragms are not quite as lightweight as electrostatics, but have the same large radiating area and much of the same sonic fidelity. They are not as efficient as regular dynamic phones, and cannot play as loudly.

You'll have to ask wualta or setmenu as to the real secrets and gritty details. This seems to be an older model T40, not one of the newer T40 RP? I'm not sure. If it is the older headphone, that's really cool - they're very rare, and you'll definitely want to hold on to these. The new RP series, from what I've heard, is not anywhere as good.

As an isodynamic, they'll want a lot of juice. I would definitely like to hear how they perform amped. Basically, isodynamics can give you a good idea of how electrostatics sound, without all the fuss that usually accompanies electrostatic headphones.

 

[RedLeader]

yea, these are ~15 years old, so are most definetly the old non-RP models

 

[catscratch]

Quote:

Originally Posted by RedLeader yea, these are ~15 years old, so are most definetly the old non-RP models

Nice! These are some top notch vintage cans. It would be very interesting to hear how they match up with the HD555 and MS-1 in your sig. I wouldn't be surprised if these old cans win.

http://www6.head-fi.org/forums/showt...ghlight=fostex

Some more information on the various Fostex phones (as well as me raving on how much I want them like an idiot). No mention of a T40, though.

 

[RedLeader]

well... he said keep them. So that means they're free! I'll do a quick compare the the 555 and MS-1, but I'll save the big review till I'm done my amp.

Highs - They're bright like the 555, but seem to have more detail. They're more laid back then either can, much more analytical. They've got the MS-1 beat hands down in the highs, no contest at all. The 555 is much closer, but I think the T40 edges them out as well.

Midrange - This is where I noticed a bit of a problem with the T40. They seem to have a slightly exaggerated midrange, with a slightly pumped up midbass section. I believe the 555 handle midrange quite well, with the MS-1 being an obviously more forward sound. Again the T40 is a more laidback and analytical sound, even with the prominence of the midrange. The 555 is known to be a more forward sounding sennheiser, so I would put the T40 closer to the 580 sound in this sense. This one is a toss-up, but my favourite is the MS-1

Bass - When driven properly, they have more extension than either the 555 or the MS-1. While less punchy then the MS-1, it still has the fullness (or I'm assuming it will when given enough power, I'm going off high-volumes here) while giving enough of a hit to satisfy. The 555 I believe are lacking in the bass department in terms of getting down all the way. Their mid-bass is good, and the extension is good, but not great. This is a per-song preference thing. With punchy rock/metal I prefer the MS-1, with everything else the T40 wins.

Soundstage - MS-1 has little seperation, and again its a 555/T40 tossup.

I'll give a more thorough review (or write one for the reviews section) if anyone would like.

 

[catscratch]

Thanks, that's exactly what I was looking for. And you know, given the age of these things, this is pretty amazing. It's such a shame that isodynamic technology didn't get improved upon past somewhere in the mid-80's when it fell off. It could be rivalling electrostatics right now at a much cheaper price.

 

[wualta]

[eyes pop out of head, hair catches fire, knees fall off; feels faint but manages to hold onto drainpipe] I can't tell you how thrilled I am to see this headphone and especially the photos of its construction. I never mentioned the T40 because I had no idea it existed-- not with a round rather than square driver! Since it's housed in the new-style case (but with round instead of squarish earpads, I now notice) with the removable cord, I had assumed it had the same little square-type driver as in the T50RP. A presumptuous assumption on my part! Your T40 definitely has the good old-style (ie, big and round) driver, which, contrary to the description currently on the Fostex site, used aluminum for the spiral voice coil and a thin polyester membrane rather than the thick polyimide (Kapton) one of the current line.

Oh, where to begin!

To hell with it; I'll just babble:

[For the purposes of this babble, the type of driver the T40 contains is most commonly called an isodynamic driver, but it has several other names: orthodynamic, magnetostatic, planar, planar-magnetic... I just call 'em "flat-driver" 'phones, but that's me.]

First, thanks to RedLeader for a review that really conveys a sense of what it was (and is) like to listen to an isodynamic headphone. Among other things, his review gives the lie to the assertion that this type of headphone doesn't play loudly. I think it's been demonstrated that not only is it capable of playing loudly, it will do so while still retaining its cardinal virtues, clarity and coherence.

Not as efficient? Efficiency is all about the magnets. If they'd had neodymium-iron-boron magnets back then, they'd play just as loud as, say, AKG K501s do today; maybe louder.

I had no idea Fostex made their drivers disassemblable, and thus repairable! All other isodynamic 'phones I've seen have glued or clamped the magnets and diaphragm together into a solid unit (I've never disassembled my older Fostexen). Assuming the diaphragms were available as a separate part, you could do repairs in the field in less than a coupla minutes. Makes sense for a pro audio product.

RedLeader, what's the diameter of those magnets?

Fostex, if they had good reasons to make diaphragms that weren't always critically damped, at least understood that this kind of driver greatly benefits from it; it's also true that a critically damped diaphragm will have bass that at first sounds rolled off compared to underdamped bass, so you'll want to add just a bit of deep-bass boost (and maybe goose it a bit on the high treble). When you do that you'll find the clean 'smacktile' [smack + tactile] bass you crave, and then some, because a critically-damped diaphragm gets harder and slammier when you feed it more bass, whereas a "cheater" diaphragm (one that's underdamped to give the impression of more bass) only gets flatulent and mushy when pushed hard. With a proper amount of boost, an old Fostex will give you bass that's positively speakerlike. You'll need something like a vintage (circa 1980) integrated amp or the modern equivalent, if you can find one, to give them enough oomph to do their thing. If their diaphragms aren't tensioned too high, the bass on an isodynamic 'phone goes very deep indeed. And I don't know of any other type of headphone except an electrostatic whose structure allows a user easy access to damp it to any degree desired.

By the way, the stated similarity to planar-magnetic speakers is not quite true in every respect-- I've found that most planar-magnetic speakers (Magneplanars in particular) are single-ended, ie, the magnets are placed on only one side of the diaphragm. Get enough rock'n'roll going and the diaphragm moves out of the linear portion of the magnetic field and you get distortion big time. A designer can get away with this if there's enough diaphragm surface area so that max excursion can stay low. The Fostex (and all other isodynamic 'phones I'm familiar with) are more like a modern electrostatic-- double-ended, which is another way of saying push-pull. Much more linear, much less distortion at high excursions. To put it in plain English, the Fostexen use a design that's superior to most (not all-- Eminent Technology speakers are push-pull) planar-magnetic speakers.


.

 

[wualta]

Quote:

Originally Posted by RedLeader well... he said keep them. So that means they're free!

Agh! Lucky #$%@ devil!


Quote:

I'll give a more thorough review (or write one for the reviews section) if anyone would like.

I'd like!

I'd like to get hold of a T40, too.

Gotta have 'em... [starts pacing]

A server reboot or something must've erased RedLeader's original photos, which I happened to save. Here are three of them:

 

[tyre]

I recently acquired a pair of Fostex T20 isodynamic headphones. So I guess this is what neutral is supposed to sound like. They sound pretty good, although they seem slightly dull compare to a pair of SR60's. They are very non-fatiguing and comfortable too.

 

[doobooloo]

Quote:

Originally Posted by RedLeader yea, these are ~15 years old, so are most definetly the old non-RP models

Not so - in your photos, there is the very clear RP logo embossed on your phones...

 

[wualta]

Quote:

Originally Posted by tyre I recently acquired a pair of Fostex T20 isodynamic headphones. So I guess this is what neutral is supposed to sound like. They sound pretty good, although they seem slightly dull compare to a pair of SR60's. They are very non-fatiguing and comfortable too.

Good score, Tyre! They look to be in excellent shape cosmetically. If they've been cared for properly, their mono image should be just about perfect. To explain: reproducing a mono signal is surprisingly still difficult for many headphones. Ideally a mono image should be a paperthin line of sound appearing to dance on the bridge of your nose. If its left and right drivers were matched carefully, a headphone will throw a good mono image. Which means it will also throw a clean, accurate stereo image. Fostexen (Fosteces?) seem to be particularly good at this, which may be one reason why they were so expensive back in the '80s.

Here's an exploded diagram of your T20RP [UPDATE: Fostex has removed the diagram and parts callout. All traces of the what we here on HF call the T20v2 have been wiped from the site]. Fostex made it very difficult to differentiate between the T20RP you have (squarish cup, round earpads, round driver), and the newest T20RP, which they call the T20RPmkii, which has the squarish cup with bigger, rectangularish earpads and the comparatively lousy-sounding little square driver. Whew! [UPDATE: We've since found to our horror that the driver wasn't and isn't at fault so much as the earpads Fostex was using. Search recent posts about the T50RP or "T50RPv2"]

When I got my T50RP a few years back ('02) and discovered it wasn't up to expectations, I assumed that all the Fostex line had been given similar little square bass-free drivers; it turns out they hadn't-- the second-version T20 and first-version T40, still had the good 45mm round drivers. [they went out of production at the end of 2006]

Easiest way to tell the old RP from the new RPmkii? The model number printed on the earcup of the older gooder style doesn't say Tx0RP, just Tx0. The newer uckier style [but see 2nd paragraph above] says Tx0RP, and there's a white stripe with a small "mk ii" in it underneath. Also, the raised, stylized RP logo is white on the new mk ii models.

Note that all of these headphones have the raised RP logo because all of them are Regular Phase (Fostex's trademark for isodynamic) 'phones.

As I said earlier, if you keep them stock you'll want to try giving them some really deep bass boost and give the treble a tweak upwards. Use a real amp (or an old preamp with good EQ, e.g. Yamaha C-80/85) and you may get to like neutral, prefering it over the euphonic but definitely colored (and less extended) SR-60.

UPDATE: I did acquire a T40, the same kind RedLeader has, but I've still never heard any of the T20s [UPDATE TO THE UPDATE: Now I have, and the second-version T20 (the one Tyre is talking about) is the mod champ, although the modded first-version T40 is super-easy to mod and once modded has an electrostaticlike charm all its own] so keep us up to date as you live with them and accumulate impressions.

.

 

[smeggy]

Wharfedale isodynamics gave me my first and best eargasm ever in 1976 or 77, so you can count me in with the bunch who love planar earspeaker designs. I miss my old wharfedales, though I imagine they'd sound pretty crappy now. I actually took a pair apart once to see how they were made, big and square with dished magnet plates. Fascinating stuff.

Congrats on your new aquisition and happy listening

 

[Gino]

Wow, I am amazed the earpads are still in good condition. I thought they would have been cracked after 15 years.

 

[RedLeader]

not only that, but the internal wiring and everything is in perfect condition. I've been listening to my dt990, but now that this thread popped back up, on they go again. I was debating selling them as I dont use them alot (I prefer open to closed) but these are just so darn cool...