Наушники — Koss PRO4AA

The PRO4AA, also written Pro/4AA, is a full-size closed-back over-ear headphone from Koss Corporation of Milwaukee, Wisconsin, built for studio monitoring. Koss introduced it in 1970 and describes it as the first dynamic headphone to deliver true full-frequency, high-fidelity performance, combined with noise isolation. The model was retired in the late 1980s and returned to the range after demand from buyers, and it remains in the current catalogue at USD 114.99. The 1971 list price was USD 50.

Key specs that matter

Both earcups use a 50 mm dynamic driver. Koss quotes a frequency response of 10 Hz to 25,000 Hz, an impedance of 250 ohms and a sensitivity of 95 dB SPL for 1 mW, with distortion below 0.1 percent. The cable is a coiled, single-entry lead of 2.4 m that terminates in a 6.3 mm plug. The headphone weighs about 641 g and measures about 109 x 262 x 257 mm.

Engineering and use context

The closed, noise-isolating earcups were designed for the needs of broadcast and recording work, and Koss notes that the PRO4AA has remained a staple in radio and recording studios. The construction is heavy, with a durable, adjustable headband and padded ear cushions, and the clamping force is firm. The single-entry coiled cord runs into one earcup only, which keeps the second side free of cable, and the coil lets the lead stretch when the wearer moves away from a mixing desk or console. Koss sells replacement PRO4AA ear cushions as a set that includes two cushions and the screen and foam assembly, and the company states that these fit both new and older production units. Like the other wired models in its range, the PRO4AA comes with a Limited Lifetime Warranty, and Koss says it continues to honour claims on units bought decades ago.

Pairing

This high impedance with moderate sensitivity needs more drive voltage than a phone or laptop headphone output typically supplies, so a dedicated headphone amplifier, a mixing console, a studio interface or the headphone socket of a full-size amplifier or receiver is the natural source. The large plug fits these sockets directly, while a 3.5 mm adapter is needed for portable devices. The long coiled cable suits connection to studio gear or a home system at a distance from the listening position.

Alternatives

The Koss UR20 is a lighter closed over-ear model with a 32 ohm impedance, 97 dB SPL sensitivity and a long single-entry cord at USD 24.99.