The Westone B50 features a full-range, five balanced-armature driver with 118 dB SPL @ 1mW sensitivity, 10Hz – 20kHz frequency response, and an impedance of 35 ohms @ 1kHz, 25dB passive noise attenuation
The Westone W40 features a full-range, four balanced-armature driver with 118 dB SPL @ 1mW sensitivity, 10Hz – 18kHz frequency response, and an impedance of 31 ohms @ 1kHz, 25dB Passive Noise Attenuation