Sennheiser HD 400 PRO reference headphones aim for 'all the tiny details'

Sennheiser is back with another pair of reference headphones targeting professionals, studios, and anyone who needs to clearly hear every subtle note in an audio project. The Sennheiser HD 400 model boasts a wide frequency response beyond that of consumer headphones, exceeding the audible range to ensure even the most nuanced sounds are perceived.

Reference headphones are designed to offer a pure audio experience. Music is delivered unaltered from its source, meaning the hardware doesn't introduce an artificial boost in bass or treble, doesn't smooth out pitchy sounds, and otherwise maintains a very neutral profile.

Sennheiser says it designed the HD 400 PRO to "reveal all of the tiny details" in music. The model marks the company's first PRO reference headphones with an open studio design, presenting the improved soundstage, clarity, and audio depth associated with open-back earcups (via Audio Advice).

Generally speaking, headphones sport closed-back earcups in order to prevent sound leakage — and it's this same design that makes reference headphones unsuitable for use at the office, on the bus, or anywhere other people are nearby.

The audio company paid special attention to studio needs when designing the HD 400 PRO. For example, the model features 120-ohm transducers embedded at a "slight angle" in order to replicate the same position in which an audio producer would listen to content with monitor loudspeakers.

The transducer arrangement combined with the open-back design, says Sennheiser, results in "a wide and spacious soundstage" with neutral, accurate audio reproduction. The headphones are crafted to offer the user comfort during long listening sessions, including soft velour earpads and an ultra-light frame combining "minimal pressure" with careful positioning to "gently" hug the user's ears.

The HD 400 PRO features an expansive 6 to 38,000Hz frequency response, sub-0.05% distortion, 120-ohm impedance, 110dB sound pressure level, and a 3.5mm audio jack. Sennheiser packs both straight and coiled detachable cables with the headphones, as well as a 1/4-inch (6.3mm) audio jack adapter for use with professional audio equipment.

Despite its number of features, Sennheiser has made the HD 400 PRO a reasonable option for audio professionals who have modest budgets. The model is priced $249 USD / £219 GBP, undercutting certain competing models like the $500 Shure SRH1540 and $349 Audio-Technica ATH-R70x.