AKG K-500

Not much is documented about the AKG K-500. The trade press suggests it was an open-sounding monitoring headphone sold in the early 1990s alongside the AKG K-400. A pro-audio new-product guide from late 1991 lists the pair as AKG's monitoring headphones. A mid-1992 roundup praised the K-500's very open, natural sound and credited a large-diaphragm transducer.

The best surviving record is a Hirsch-Houck Labs test report in Hi-Fi-Stereo (February 1992, p.41). They measured on a coupler that simulates the air volume around a typical listener's ear. The K-500's impedance was 130 ohms at 110 Hz, dropped to about 100 ohms at 20 Hz and 1 kHz, and rose smoothly to roughly 150 ohms at 20 kHz. At 50 Hz, distortion was mostly second-harmonic - 2.2 percent at 1 volt, rising to around 7 percent at higher drive levels (9-220 mW). Mid- and high-frequency distortion was negligible. An FFT noise-burst (MLS) measurement reproduced the shape of the swept sine-wave response, with irregularities of about the same size.

Past that, the record thins out. No production years, original price or detailed engineering background have surfaced in the surviving documentation. The K-500 shows up in 1991-92 publications and then fades.