This full-size professional quality stereophone has long been the headphone of choice for broadcast and recording professionals whose careers demand reliable equipment and superior performance. As the first dynamic stereophone to deliver true full frequency, high-fidelity performance, the PRO4AA set the standard when it was introduced in its original form in 1970. In the late 1980s after long service, it was retired and replaced by a newer model. Customers clamored for its return, and by 1988 it was brought back by popular demand. Since then, though we've incorporated performance-enhancing technology and updated its style, the essence of the PRO4AA remains unchanged and it continues to set the standard for performance and reliability today.The PRO4AA features dynamic elements for an exceptionally wide frequency response from 10-25,000 Hz. Designed for frequent use over extended periods, the PRO4AA's durable steel and rubber headband is generously padded. Adjustable slide bars ensure a snug fit, also critical for hearing every note and keeping unwanted sounds out. The heavy-duty, single-entry ten-foot coiled cord affords ample flexibility of movement. It includes microphone mount hardware for complete versatility. The PRO4AA has a 6.3mm (1/4") plug and an 8 foot coiled cord.Whether you are a sound professional or simply love music, the PRO4AA will deliver excellent isolation, accurate sound reproduction, and the excitement of a live performance to your recording. Built to last, the PRO4AA is covered under Koss’ Limited Lifetime Warranty - the only warranty of its kind in the stereophone industry.