[wualta]

Yes, it's hard to believe, but I found a K340 for a decent price, and it's still undergoing the normal descaling and steam cleaning processes old studio 'phones have to go through here at The Lab, but I did do some preliminary tests and took some photos so all the aficionados can tell me when they think this pair was made and what sort of mods will be suitable. It's apparently the bass-normal version, because without EQ both ends sound rolled off, though the mids are flat. No "AKG" logo on the headband.

The earpads were dirty enough to require a couple of cycles in the washing machine. While those dry out and get the leather-restorative treatment, an old set of Sony replacement earpads that were sold to me years ago by a dealer suspiciously eager to convince me they were the exact replacements for my Sony ECR-500's pads are filling in. Very comfy, though they force the ear away from the diaphragm and are responsible for some of the bass-normal sound. Inside, the electrets appear to be unprotected from hairs, dust and moisture! Mine required a good vacuuming. Channel balance is perfect. Passive diaphragms are ivory colored and backed by gray damping screens.

I've always thought the passives were a way of acoustically "unsealing" a closed-back headphone-- using resonant diaphragms like ports in a bandpass enclosure to vent some frequencies to the atmosphere and gaining the low natural resonant frequency of an open 'phone while retaining the seal of a closed 'phone, and I don't think I was far wrong. But the passives are just diaphragms, not "drivers". They don't produce sound. The passives don't "form the crossover" either. They perform the same function as the vents in the K501-- they let certain frequencies from the backwave of the dynamic ( = bass + midrange) driver get into the earcup. Each diaphragm is tuned to a different frequency and is damped by the plastic screen behind it (and the cotton). The idea is to let controlled amounts of antiphase midrange frequencies enhance the spatial abilities of the 'phone without cancelling the bass, a really neat idea, though undoubtedly expensive. Call it Tuned Leakage.

Back to the 'phones at hand: The elastics in this sample are game but tired. Is there a way to increase the tension, or must they be replaced? [Editor's Note: Oh tsk tsk. Wualta (and any interested modsters) should consult KT88's compilation of the major K340 mods. If it'd been a snake, it woulda bit him; it's right here.]

I see why people cut out the plastic earcup grille, because as you can see in the second photo, the holes in the grille only randomly align with the holes in the electret driver. For high frequencies, this isn't that much of a problem, and the electret badly needs protection. You should've seen the crud I vacuumed out of mine. But still... something like window screening would be better.

Has anyone traced out the circuit on the little "crossover" circuit board? EDIT: It's not a crossover. Not in the usual sense... turns out...

...the original K340 brochures were correct. This simple circuit controls the level of the electret versus the dynamic driver. There is no filter network to "bypass". Both drivers operate wide open, so to speak.

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[Carl]

I'm surprised The Lab took so long to procure one. It's practically right at home there. Try to track down its much forgotten about younger sibling, the K145, too.

 

[Blackmore]

I am sorry to tell, but they are not that fresh looking at all. Been used pretty heavy, I guess

 

[wualta]

Quote:

Originally Posted by Blackmore I am sorry to tell, but they are not that fresh looking at all. Been used pretty heavy, I guess

Ya think? You should see the plug-unplug wear scratches on the plug. It's almost worn through the chrome. This thing has been USED. Yet it soldiers on with no: missing bits, blobs of epoxy, gaffer's tape or any signs of ad-hoc adhockery or abuse.

Stock, it's pretty much what folks have said, soundwise: good, but nothing special. Takes hella bass EQ gracefully (though not as gracefully as the Yama Orthos or the Stax Lambda Pro), and the topmost highs are there with a little help, though nothing to build a cult on. But that's stock. Mods will tell. As it is, it's reasonably smooth and flat and there's no distortion, so I assume it's operating at original design spec.

Quote:

Originally Posted by Carl I'm surprised The Lab took so long to procure one. It's practically right at home there. Try to track down its much forgotten about younger sibling, the K145, too.

Don't forget the K4.

It took so long because every friggin' auction shot through the roof. I was determined not to pay more than $100 for one of these things.

"Right at home".. well, I've always considered AKG's 2-Way Obsession Period to be technically interesting but not likely to produce sound that's a leap above a good one-way. I could never figure out if they were after an existing level of quality for lower cost, or a leap ahead in absolute performance. And The Lab believes that all things being equal, crossoverless is the way to go.

Today the real earpads should be dry (they're cracked but intact). I bet they'll make a difference.

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[facelvega]

And? Any difference?

As you know, I happen to be fond of my only lightly-modded K340, and am also a member of team ortho. I'd even go so far as to say that my K340 is better than my best ortho, the PMB100, at much music. But then again the PMB100 is really only outstanding for very specific things, and almost subpar at others. (Lately, however, I'm mostly listening to my Koss A250, which is also no slacker, and happens to be the only one of the three currently in my office.)

On the other hand, I do find the K340 a bit frustrating: it's so amp-sensitive, and it really needs to be cranked up to sound good. Too much so for prolonged listening, in my opinion. And yes, not as inspiring as it should be from the cult status. Though I speak without having really taken the modding dive yet.

ps, what makes you think the passive diaphragms were expensive? It seems like at that time AKG was stuffing them into any headphone where they would fit. I've even used them to identify that certain headphones branded Philips and Saba were actually OEMed by AKG.

 

[smeggy]

I don't suppose those earpads help. It looks like they are for another headphone as they are blocking off most of the grille, and sound. Still, I imagine with all the wear and tear they were replaced at some stage with whatever was at hand. Hopefully after some mods and a good run through the dishwasher they'll sound good.

 

[wualta]

Yes, the original pads do make a difference, and as expected it's a positive one compared to those clunky Sony pads. Not so much by unblocking the driver face (if you want to see a blocked driver, take a look sometime at the Philips N6325 electret 'phone we discussed here last year-- you can't even see the driver's surface), but by moving the ear right up to the grille. Bass is better thereby, as we'd expect. Still, the 'phone sounds rolled off mildly at both ends. Not a problem, because I wanted to hear the vaunted K340 mids, and sure enough, they were there. There's a kind of "bloom", a gradual rounded boost in the lower mids that gives voices and some instruments a sweet pop-out quality, but though it's pleasant, it's not accurate. Mellow. Warm. Plummy. I'm not complaining.

I'd call the unmodded bass soft and fluffy rather than hard and smacktile. The highs are not as smooth and sparkly as, say, a Lambda's; at least, not with a Baxandall-type boost. Better would be the boost supplied by a good parametric EQ such as is found on the old Yamaha C-70/80/85.

So: pleasant and obviously competent, but not spectacular. Pretty dang good for 1978, though. Of 'phones of that age, only the Staxen sounded better overall, and yes, the Fostex T50, but nobody had those, and they still don't, dash it all. If that sounds like a lefthanded compliment, I guess it is, but again, the mods are yet to come.

That bit about the diaphragms' expense/complexity is simply demonstrated: compare the K501 (holes chopped in the baffle which are backed by a cheap sheet of foamed plastic) to the K340 (backwave allowed entrance into the earcup, but excluding the bass backwave by virtue of the 6 diaphragms each tuned to a different carefully-chosen nonbass frequency thereby acting as damped bandpass windows). I'd say the K340 and K260 and all the other AKG dynamics that used the ring-o'-diaphragms construction were clearly more expensive to build.

But the passives did allow an openish sound in a closed 'phone, and that's an accomplishment. I haven't found any vents in the back of the K340 cups. Not yet, anyway, so until I do I'm calling it a closed design.

Again, I'm reserving ultimate judgment for mod time.

However, the original idea behind the diaphragms-- well, one of them, at least-- was to have some passive fine-tuning control over the frequency response of the headphone. Each diaphragm acts like the slider in a graphic equalizer. The mass of the diaphragm sets the frequency and the amount of cotton behind it adjusts the amount of attenuation (and, as with any simple graphic, the Q of the peak/dip and thus the bandwidth over which it has an effect). Take out the cotton and the EQ effect is stronger and more closely confined to a specific frequency for each of the diaphragms-- we would say that the Q of that acoustic "circuit" had increased. Another way to get a grip on Q is to say that the higher the Q the more the response graphs as a sharp spike. Resonances in speakers, turntables, rooms and headphones all have Q. Undamped resonances graph as stalactites or stalagmites in a frequency response curve and sound as painful as they look. Damp a resonance and you reduce the Q-- the spikes turn into gentle rolling hills. The energy in the spike is squashed and spread out.

A better way to experiment with the cotton would be to replace the cotton entirely with thin felt discs of varying thicknesses applied to the back of each diaphragm. Remember, each one is tuned to a different center frequency. Or you could simply try partially plugging up the perforated discs behind the diaphragms with tape or Juicy Fruit. You can't change the frequencies, but you can, so to speak, push the sliders up and down by varying the damping. That is, I admit, a lot of experimenting, only recommended for the truly compulsive HF personality, though just imagine the customizability.. The downside is that I'd expect the headstage of the headphone to decrease a bit.

I'd love to have a diagram from AKG showing which diaphragm is tuned to which frequency.

FV, if you like the K340 over your other orthos, I'd like to be there when you try a damped YH-100 that cost a third as much. While you're still in Berlin, keep an eye out for the K4 and K145.

And oh yeah-- if any transducer, whether speakers or 'phones, needs to be cranked way up to sound good, you know the frequency response isn't flat or anything resembling it. There's a peak somewhere that's masking adjacent frequency bands, or a trough that's dropping parts of the spectrum below the liminal threshold. The "whisper test" is one of the most revealing and difficult tests to give a speaker or headphone, and it's difficult not only for the item under test but also for the tester, since the level of background noise greatly affects the result. Still, a good rule of thumb is: if it doesn't sound good at low level, keep looking.

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[SonicDawg]

wualta, if you are interested in getting more treble energy from the K340s, you can look into biwiring them--meaning copper wires to the dynamic drivers, and silver wires to the electrat units (going from the dynamic units). It makes a world of difference in my bassy pair.

 

[Zorander]

Pardon my ignorance, but what exactly does "Ortho" mean or refer to? I've seen that word here quite often but never really checked out the meaning.

 

[SonicDawg]

I think there is a rather extensive thread on the Orthodynamic productions of the past. Look up that behemoth of word and you shall see.

btw, I am steadily gaining more respect for the technical grandeur of many of these old designs, not to mention their exceedingly supreme performance comparable to even the most cutting edge productions. That speaks a lot about the commercializing of the headphone industry today.

 

[smeggy]

Yes, it's sad to realise that there was a lot more driver variety and innovation in the '70s than now. Some were bad, some were great but at least they were trying and many companies produced cool non-dynamics that were affordable.

The only non-dynamics now are generally very expensive like the Stax, Koss 950, Ergo AMT and one other which is also over $700.

 

[Carl]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif Yes, it's sad to realise that there was a lot more driver variety and innovation in the '70s than now. Some were bad, some were great but at least they were trying and many companies produced cool non-dynamics that were affordable. The only non-dynamics now are generally very expensive like the Stax, Koss 950, Ergo AMT and one other which is also over $700.

Well, there are the current production Fostexes...

The only reason to really keep making planar headphones in this day and age is sound quality, so that's why most of them cost a bit.

 

[wualta]

For those of us who lived through the socalled Second Golden Age of Consumer Hi-Fi, which we've designated by fiat to be 1975-85, it was the best of times, it was the worst of times. The market was big, since there was no competition from cell phones, 'putas, Blu-Ray or satellite radio. So the companies were all sorely motivated to innovate as they hadn't been since the First Golden Age in the mid-late '50s/early '60s and certainly haven't been since. So we had Fi For The Proletariat, which gave us affordable high tech like the Heil driver, the hybrid 'stat speaker, the electret headphone, the planar-magnetic speaker and headphone (Orthodynamic is merely Yamaha's trade name for their planar-magnetic headphone, just as Regular Phase was Fostex's and Planar Voice Coil was Audio-Technica's) the VFET transistor, the polymer piezo tweeter and headphone, the kilowatt power amp, the microprocessor-controlled auto-everything HX-Pro-equipped cassette deck, the affordable direct-drive turntable (and by extension the beltless reel-to-reel tape drive), the first affordable no-cringe phono cartridges playing the Direct Metal Mastered LPs mastered from tapes the dawn of digital audio.. and a lot of these things were wonderful but a lot of them hit the marketplace half-cooked. They turned unreliable or proved to be expensive to produce or were simply forced out of the marketplace by cheaper alternatives (or the CD). And many of us who were young at the time couldn't afford many of them, despite mass Japanese production, or were unwilling to spend twice normal to make the leap to better tech (electrostatic 'phones, to pick a standout example).

Now, of course, the market is much smaller, isn't geared toward ultimate audio fidelity or even anything as wussy as "sound quality", and isn't likely to produce anything exciting for the masses except competent cheap speakers-- undreamt of in the '70s, make no mistake!

One thing that arrived around 1980 and has stayed with us is the Great Headphone Revolution, and here we are. Of course, if it had not been for the development and commercialization of the rare-earth magnet, the neodymium rare-earth magnet in particular, the GHR would have been much less great, and who knows, electret electrostatics might've got a foothold. But the magnets did arrive and we saw the rise of the Age Of The Dynamic Headphone in ways that were impossible to foresee back when the only people who wore headphones were the ones who had to, plus a few pipe-smoking, yogurt-swilling, Earth Shoe-wearing, Wankel-driving geeks.

Fostex, bless their little black patent leather hearts, still make isodynamic headphones, though the current crop is so specialized for pro audio that they're useless for audiophile use [UPDATE: This changed from 2008 on with a radical earpad redesign by Fostex-- see the Ortho Roundup thread]. So thanks be to that online auction site we love to hate which brings us survivors from the Second Golden Age to show us what life might've been like, if only.

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[facelvega]

Wualta, would you really say the second golden age lasted until '85? When almost all the great midfi receivers had been replaced with cheap garbage and headphones were those things that came with walkmans? I'd've thought it ran something closer to 72-82.

 

[ericj]

Quote:

Originally Posted by wualta /img/forum/go_quote.gif and Planar Voice Coil was Audio-Technica's) the VFET transistor, the polymer piezo tweeter and 'phone, the kilowatt power amp, the microprocessor-controlled auto-everything cassette deck, the dawn of digital audio

fwiw, the VFET didn't really go away. It just got refined. There were unforseen side-effects of the sharp bottom of that V, and it was ultimately replaced by a variety of vertical DMOS trench variations like the IRF HexFET.