Sennheiser: HD 400 PRO Headphones

Sennheiser, a German business run today by the founder’s grandsons, took a new direction last year. A longtime player in consumer and professional headphones, microphones, and other technologies (in addition to owning Neumann since 1991), Sennheiser spun off its consumer electronics division to Swiss hearing aid manufacturer Sonova. With their focus completely on the “PRO” audio marketplace, the HD 400 PRO open-back headphones are well suited for recording and mixing engineers.

As such, the company describes the HD 400 PRO as “A professional’s tool with neutral sound reproduction.” Features include angled transducers (designed to hold together at high SPLs), lightweight construction “for all-day usage,” velour earpads, and a choice of either coiled or straight cables. (Note: driving headphones to SPLs that cause well-designed drivers to break up audibly and distort WILL damage your hearing, so don’t do it!) In short, these ‘phones are designed for people who do much or most of their recording and mixing on headphones – an ever-growing market. The HD 400 PRO’s affordable price puts them in reach for home recordists and professionals just starting out. Note to recordists: Open-back headphones cranked loud enough will bleed into microphones. Also, they aren’t always practical for recording a loud sound source you are near, or recording in an ensemble of loud instruments. For these jobs, choose closed-back headphones.

Sound-wise, Sennheiser variously describes the HD 400 PRO as, “honest across the board, especially when it comes to the lower end of the spectrum,” “what goes in is what comes out,” and as “reproducing analytical audio.” This should make them an excellent open-back complement to the company’s Neumann NDH 20 closed-backs, which I reviewed in Tape Op #132. So, the first thing I did was listen back and forth between the two models, using my Grace m900 headphone amp (which I reviewed in #124). I spent hours with each, listening to a variety of music streaming on Qobuz, editing my recent tape transfers, and putting together a CD compilation mixtape for an upcoming road trip.

Before I describe the sound of the HD 400 PRO and how it compared to the Neumann NDH 20, I need to say that everyone hears headphones differently, due to our unique hearing curves, head size, and shape – and, in the case of fellow middle-aged audio pros, how damaged our high-frequency perception is at this stage of life. So, net-to-net, all I can tell you is what I heard; your results may vary.

The HD 400 PRO sound is lively, especially in the midrange. Not in a bad or hyped way, but rather in a way that is helpful for mixing a stereo sound field. It’s not “screamy” – like vintage Altec studio monitors – but it definitely has a strong emphasis on the focus frequencies for mixing. In contrast, the Neumann ‘phones are darker and more laid back. The Neumann’s impedance is 150 ohms, compared to 120 ohms for the Sennheiser’s, so the output volume needs to be slightly higher to drive the Neumanns. The Grace m900 headphone amp used in my testing has plenty of current to drive the impedances of both headphones, so I don’t consider the amp to be a factor in the comparison.

The Neumanns sound more like close-proximity monitor speakers (and reserved ones at that), whereas the HD 400 PROs definitely sound like headphones, with the stereophony somewhat spread out and “in the skull.” With this in mind, I’d always check my mixes on trusted full-range speakers at comfortable listening levels. Be careful not to overdo the low end or underdo the upper midrange with these ‘phones. Do a few mixes, and your ears will adjust the differences. Dear Reality, a subsidiary of Sennheiser, has recently released a software plug-in called dearVR MIX (review upcoming), which simulates the sound of various rooms and speaker setups and works with other headphones beyond the HD 400 PRO.

For a final comparison, I hauled out my favorite headphones, the Sennheiser HD 650 [Tape Op #43]. I know these headphones back and forth and understand how they differ from my various monitor speakers. Like the HD 400 PRO, the HD 650 puts the sound more “in your head” than speakers in a room. But, the HD 650 has less of that upper midrange shine and heavier low end response – more akin to how full-range speakers sound if they can accurately and quickly resolve bass information.

It’s important to know both the Sennheiser HD 650 and the Neumann NDH 20 cost twice as much as the HD 400 PRO. I wouldn’t say they’re both twice as good, but both are more honest about how the low end will sound with full-range speakers. I think the HD 400 PRO would be more useful than the Neumanns for constructing a complex mix because they define the stereo field more sharply, allowing precise placement of sounds. But, as I said earlier, check the mix on good speakers in a known room.

As far as physical comfort, the HD 400 PRO are the lightest weight of the three, and the fit and feel of the earpads are similar to the more expensive HD 650s. That’s a solid “thumbs up” if you’re wearing headphones for long periods. As for the choice of coiled or straight-wire cables, the coiled cable has an annoying resonance that makes any rubbing or scraping very audible in the left ear, from the top of the cable through the first few coils. From there to the connector, no resonance. The straight cable doesn’t have that resonance below the first few inches from the ear, meaning it won’t distract as it rubs against your shirt. Both cables connect to the left earcup with a somewhat finicky, but secure, twist-lock mechanism.

Because everyone’s hearing ability and head shape are different, headphone preferences are about the most personal thing in pro audio. If you’re seeking a comfortable headphone good at reproducing location-cue information without sounding harsh or overhyped, the Sennheiser HD 400 PRO is worth an audition.