AKG K-240
Sixty-nine dollars and fifty cents bought you a headphone AKG called the first "totally sound-and comfort-engineered" design.
Overview
The K-240 is studio gear that stopped being a product and became furniture. AKG's own catalog copy from the period billed it as "the first totally sound-and comfort-engineered headphone." It at least names the two things that mattered: how it sounds, and whether you can wear it for a ten-hour session without wanting to throw it across the room. The same catalog page describes "extreme comfort with virtually no fatigue under prolonged use." The design also survived for decades with only revisions rather than replacements.
Pricing in the period was modest. AKG's list price was $99.00, but distributors sold it for $82.75. By the time HiFI-Stereo (June 1976, p.28) put it through the lab, the price of the AKG K-240 was $69.50. That's a big drop over a few years. The headphone was being pushed into both the home and professional markets, and it was priced like a tool, not a trophy.
HiFI-Stereo measured the phones on a modified ANSI headphone test coupler. The report is candid about the limits of that method: the ear cavity itself can have a profound effect on frequency response, especially at middle and high frequencies. So the measured curve and the subjective listening didn't line up perfectly, but in the K-240's case the divergence was small. The magazine's verdict was that the listening quality was not too different from what the measurements predicted, and that the sound was "extraordinarily clean."
The impedance is the part that trips people up. The original K-240 was a 600-ohm design. A builder in the archive's technical material notes that with AKG K240 headphones the amp "couldn't drive as loud before reaching the onset of clipping" because these are 600-ohm headphones that "require quite a lot of voltage." That's a design choice aimed at studio consoles and headphone amps with real voltage swing. The high-impedance load is easy on a proper amplifier and miserable on a weak one, and the archive's own notes call it "marginally acceptable" on a small tube headphone amp. The later K-240 Studio reworked this entirely. A 2002 EQ Magazine (May 2002, p.73) advertisement for the K240 Studio cites a 55-ohm impedance with an XXL transducer. A 600-ohm original and a 55-ohm Studio share a name and a silhouette and not much else in how they behave.
Sensitivity is quoted at 117 dB SPL. Feed it enough voltage and it gets loud without strain, which is why the high impedance wasn't a dealbreaker in the studio. The design is open-back, so it leaks sound in both directions. That made it a monitoring headphone rather than a tracking one. Engineers wore them to check a mix, not to overdub a vocal while a drummer was in the room.
The archive's own material repeatedly uses the K-240 as a benchmark for other gear. A speaker review notes that harsh material "sounded overly edgy or harsh on horn tweetered speakers (but not in, say, AKG K-240 headphones)." That's a backhanded compliment, but a real one. A 1980s recording feature shows a pair of K240-DFs in a portable DAT rig.
AKG kept the name alive across generations, and the marketing language shifted. A 1978 buyer's guide advertisement in HI-Fi-Stereo-Buyers (March 1978, p.7) pitched the headphones alongside AKG phono cartridges, describing each model as "bio-acoustically engineered, lightweight, comfortable to wear." That's the same comfort-and-sound pitch in the decade's vocabulary. By the 2000s the copy had moved to "legendary headphone family" and "industry standard." The K240M is named in that later advertising as an industry standard alongside the K141M.
For collectors and users alike, the practical questions are version and condition. The 600-ohm original is the historically significant one and the fussier one to drive; the later 55-ohm Studio models are easier to live with on modern gear but are a different product wearing the same badge. Pads and headband elastics are the usual wear points on any K-240 of this vintage, and the open-back design means the foam and grille materials are exposed to decades of studio air. None of that is unusual for a headphone this old, but it's the difference between a $40 find and a $150 one. The sound the period reviewers described — clean, honest, not flattering — is the reason people still seek them out, and it's also the reason they're not for everyone. If you want bass slam and isolation, this isn't it. If you want to hear what a mix is actually doing, the K-240 has been doing that job since the 1970s, and the lab reports back up the reputation.
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