The KEF M400 sits in the middle of KEF’s M-series portable headphone range, positioned above the M100 in-ear earphones and below the over-ear M500. Launched as a compact on-ear design aimed at commuters and mobile listeners, the M400 draws on KEF’s long history of transducer engineering to deliver hi-fi-grade sound in a foldable, lightweight form.
Construction and Design
The M400’s frame is precision-machined from cast aluminium, giving it a robust feel despite a total weight of just 175 g. The ear cups pivot on a tri-axial swivel that allows the pads to conform to individual head shapes, while the headband extends without ratchets for stepless fit adjustment. The closed-back on-ear design uses faux-leather padding on both the headband and ear pads, chosen to balance comfort against the mild passive isolation the -20 dB noise attenuation figure describes. The Champagne White finish pairs a white headband and ear pad leather with a metallic silver aluminium cup body and champagne gold hardware accents at the headband joints and cable entry point.
Driver Technology
Each ear cup houses a 40 mm full-range dynamic driver with a neodymium magnet and a CCAW (copper-clad aluminium wire) voice coil. The CCAW construction reduces moving mass compared to a conventional copper coil, contributing to the quoted sensitivity of 101.5 dB ±4 dB (IEC-318 at 1 kHz) from a 32 Ω nominal impedance load. Maximum rated input power is 30 mW. The quoted frequency response spans 20 Hz to 20 kHz.
Connectivity and Accessories
The M400 is supplied with a 1.3 m cable terminated with 3.5 mm jacks at both ends, making it user-replaceable. The cable incorporates an in-line control unit with a microphone for hands-free calls and playback control, optimised for use with Apple devices. The headphones fold flat for storage and travel. Included accessories are a zip-up carrying pouch and an airline flight adaptor.