Stax Srx MK3 Headphones With Srm-1/Mk-2 Amplifier Tested Sounding Perfect, Probably the best headphones we ever tested. They are close to brand new.

The Stax SR-X MK3 headphones are vintage electrostatic "ear speakers" known for smooth, natural sound, requiring a dedicated Stax energizer (like the SRD-7) for their ~230V bias, featuring 1.5-micron diaphragms, a wide frequency response (e.g., 20-70kHz), and operating on a unique electrostatic principle, not typical wired specs. Key is the bias voltage (Normal or Pro) and their need for an energizer, not standard headphone jacks. Key Specifications (Varies slightly by variant, especially Normal vs. Pro bias):

• Type: Electrostatic Earspeaker (Open-Back, Over-Ear).
• Sound Principle: Electrostatic (Requires Stax Energizer/Amp).
• Diaphragm: ~1.5 micron (same as Gamma/Alpha Pro).
• Frequency Response: Often cited around 20 Hz - 70 kHz (tolerance unstated).
• Sensitivity: ~97 dB SPL @ 100V RMS (with 230V bias).
• Max Output: ~110 dB SPL (with 230V bias).
• Bias Voltage: Normal Bias (e.g., 230V) or Pro Bias (580V).
• Weight: Around 290g (without cord).
• Connection: Proprietary Stax 5-pin connector (to energizer).