The Fostex T40RP is considered an industry standard in the USA and are mechanically and electrically resilient.
They incorporate the Regular Phase System which promotes low distortion, high output and long term reliability. The T40RP is a closed-back design using diaphragms with exceptionally low mass enabling them to remain linear even at extremes of the frequency spectrum.
Frequency Response: 25Hz - 20kHz
Max SPL: 116dB
Impedance: 50 Ohms.
All parts and assemblies are screwed together ensuring simple field service.