[wualta]

After seeing Jude's exploded K340 diagram in an earlier thread, I started getting little signals from the far side of my brain. Using a Townes-Schawlow maser amplifier, these signals are now large enough to be examined, and my brain has decided that they are bits and pieces from old audio magazines doing their tests on the K340 when it came out in 1978. What I remember about the passives may shed some light on the mysterious midrange/headstage spell these old dinophones reportedly weave.

As I recall, basically they're windows that are open only in a certain range of frequencies. That means the 'phones behave as sealed 'phones where you want them to be sealed (in the bass) and are open-- acoustically transparent-- where you want them to be open (anywhere except the bass). My rough guess is that they're weighted to resonate around 1--2KHz, and the acoustic resistance behind them lowers the Q of this resonance and spreads the "window" over a larger range of frequencies. You can check my guess by listening at very close range to the 'phones playing on someone else's head. Do you hear mostly mids? Mids and highs?

Anyway, if I'm correct, owners should hear solid, non-phasey bass and nicely open and airy mids, the frequencies the brain mostly uses for localizing. A very clever design. Best of both worlds, don't you know.

I don't think the passives play a role in the crossover between the electret tweeter and the moving-coil diaphragm, which reportedly takes place up around 4KHz, which means the K340 is primarily a dynamic 'phone with an electrostatic clerestory, but I'm willing to listen to any good story, even one about a Zen panda.

 

[philodox]

Interesting... its hard to say if you are right, but you did describe some of the K340's characteristics well. Have you ever had a chance to hear them yourself?

 

[wualta]

Quote:

Originally Posted by philodox Interesting... its hard to say if you are right, but you did describe some of the K340's characteristics well.

It's you guys that've described them well. I have a fuzzy memory that back in '78 I thought the design was fascinating and wanted a pair someday. I was making binaural recordings back then and found that open headphones invariably gave superior listening results despite the lack of deep bass. The K340's design showed you could, on paper, have both. The way you've described them, there's a good possibility they succeeded, which makes me wonder why the design was a dead end. Too expensive to manufacture?

The only downside I could see to the K340 (again, on paper) was the 2-way design, but at the time AKG was nutso for 2-way designs. They even came up with a 2-way microphone. But crossovers are almost always necessary evils. [update: The K340 has no electronics inside that act as a crossover circuit. Serendipitous use is made of the drivers' natural bass and treble rolloffs-- clever, but not uncommon speaker practice. Owners who believe they've performed a 'crossover mod' have only moved a couple of wires.]

I don't see a reason why AKG couldn't have run the dynamic element wide open and let it cross over to an intentionally bass-shy electret tweeter (say, a small one) naturally, with no electronic interference [update: as stated above, this is exactly what they did]. In fact, why'd they make the electret element so big? Above 4KHz, it only needed to be the size of a quarter. And bla bla bla.

 
Quote:

Have you ever had a chance to hear them yourself?

Sadly, no, though I've put them on my eBay search 'bot. Any other good places to look for the K340? And how about the successor K4 and K145?

 

[philodox]

Quote:

Originally Posted by wualta The only downside I could see to the K340 (again, on paper) was the 2-way design, but at the time AKG was nutso for 2-way designs. They even came up with a 2-way microphone. But crossovers are almost always necessary evils, which means your connecting the dynamic driver directly to the feed was a positive move both theoretically and, as it turned out, practically.

Yeah, when aerius modded his headphones, this one small change made a really big difference. Quote:

Originally Posted by wualta I don't see a reason why AKG couldn't have run the dynamic element wide open and let it cross over to an intentionally bass-shy electret tweeter (say, a small one) naturally, with no electronic interference. In fact, why'd they make the electret element so big? Above 4KHz, it only needed to be the size of a quarter. And bla bla bla.

You should write an email to AKG bitching them out and telling them to get to work on the K340 mkII!

Quote:

Originally Posted by wualta Sadly, no, though I've put them on my eBay search 'bot. Any other good places to look for the K340? And how about the successor K4 and K145?

Never heard of these... I will look into it.

 

[wualta]

Quote:

Originally Posted by philodox You should write an email to AKG bitching them out..

Excellent idea!

[runs off to writing table, sits down, whips out Waterman pen, sheet of 30 lb. foolscap and a can of 30-weight]

"Sirs! I should like to complain in the strongest possible terms anent the alleged engineering in your K340 stereokopfhoerers. You call that engineering? Why, as I was telling my friend Sir Harry Ricardo only the other day..."

 

[philodox]

LOL... that was great.

 

[EdipisReks]

Quote:

Originally Posted by wualta Excellent idea! [runs off to writing table, sits down, whips out Waterman pen, sheet of 30 lb. foolscap and a can of 30-weight] "Sirs! I should like to complain in the strongest possible terms anent the alleged engineering in your K340 stereokopfhoerers. You call that engineering? Why, as I was telling my friend Sir Harry Ricardo only the other day..."

roflmao! i really want to hear a pair of K340's.

 

[wualta]

Quote:

Originally Posted by EdipisReks i really want to hear a pair of K340's.

>cries< So do I!

Y'know, thinking about that big electret element has started to bug me. I wonder... do you suppose... Where did that big electret driver come from?

Am I correct in assuming that the electret completely covers or blocks the "view" of the dynamic element (why would they risk that?) ? A guess is that they were actually working on a full range single-element electrostat model and subsequently dumped the design in favor of the K340, which eliminated the big transformer box every other electrostat of the time required. ... which makes me wonder what the electret element would sound like if it were driven full range.. or at least crossed over at say 1KHz or 500Hz. Yessir, got to get me one of them K340s... and a prybar..

Damn, I'm evil.