Koss PRO 4AA (1970)

Full-size wired stereo headphones introduced in 1970, designed for high-fidelity listening with a closed-back studio build.

Overview

The Koss PRO 4AA is a pair of full-size, over-ear, wired stereo headphones manufactured by Koss Corporation of Milwaukee, WI. Introduced in 1970, these closed-back studio headphones were recognized for their noise-isolating design and professional audio performance. Marketed under names including "Koss Pro4AA" and "Koss Pro/4AA," they remain associated with 1970s studio and audiophile use.

Specifications

Impedance	250 ohms
Sensitivity	95 dB/mW
Driver Size	50 mm
Weight	22.6 oz
Dimensions (Height)	4.30
Dimensions (Length)	10.30
Dimensions (Width)	10.10
Cord	Coiled, Single Entry, 8ft
UPC	0021299102725
UNSPSC	43201500

Design

The PRO 4AA features a closed-back, noise-isolating design with full-size 50 mm drivers and a coiled single-entry 8-foot cable. Built as over-ear wired headphones, they are constructed for studio monitoring and durable long-term use.

Context

Introduced in 1970, the Koss Pro/4AA was recognized as the first dynamic headphone to deliver true high-fidelity performance across the full audio spectrum. It set a new standard for professional-grade over-ear headphones and helped define the expectations for studio monitoring and audiophile listening during the 1970s.

Market

The Koss PRO 4AA had an original list price of $50 in 1971 and currently sells new for $85.00 to $114.99. Used units can be found for as low as $10, while