CES 2018

Better start here...it's where I started the show...I'm sure you are curious too.

The Sennheiser HD 820 is a sealed headphone based on the now famous HD 800. The remarkable thing about these headphones is the toroidally shaped diaphragm, which, Sennheiser claims, produce a more planar wavefront to interact with the ear more naturally. A dynamic headphone with a planar headphone's acoustic, if you will.

Not sure whether it works as advertised or not—heck, planar headphones can break up and produce less than coherent wavefronts—but the Sennheiser HD 800 is renowned for it's clean transient response. It's also widely thought of as an analytical and bright headphone, which Sennheiser addressed in the more soothing but slightly less responsive to my ears HD 800S.

Now Sennheiser has turned its ear toward a sealed version of the headphone. Unfortunately, Axel Grell, Audiophile Portfolio Manager, was not in the booth, but I assume this $2399 headphone is targeted at the high-end audiophile and audio professional market.

I listened to familiar music on my Astell&Kern AK240. The background noise was fairly loud and the HD 820 provides some isolation, but isn't a high-isolation sealed can. I felt it was moderately bass-shy but other wise seemed really tight. It sounded like the decay was very quick. I also didn't hear any of the annoying 6kHz peak found in the earlier HD 800 and damped in the HD 800S. I was told this isn't the final tuning but a pre-production prototype. Seemed to have a lot of promise...show conditions and all that.

Probably the most obvious and talked about feature is the concave gorilla glass plate covering the rear center of the ear capsule revealing the intricate, and to my eye beautiful, area at the rear of the driver. Completing the outer seal, rigid panels cover what would otherwise be the open mesh materiel of the HD 800/S. Pads apear thicker and more sealing than the other models.

As I said, I didn't get to talk to Axel, but here's my take on what I see going on:

Acoustic energy from the rear of the driver will tend to be reflected/redirected by the curved glass outwards and away from being directed back towards the rear of the driver. Now, that's an oversimplification because only very high frequencies are small enough to actually 'reflect' off the glass. At 1kHz, for example, the half wavelength of sound is about six inches, which means you have to have about six inches of space in all directions for sound at this frequency to truly reflect. A 6kHz tone would have a half wavelength around and inch, which is getting closer to the size needed for the 'wave' to interact in the volume behind the driver of the HD 820.

Anyhow, rather than thinking of a wavefront reflecting, think sound as blobs of sound pressure escaping from the rear of the driver. It does seem to me that these blobs of sound are about the right size from 5kHz and up to be guided by the shape of the glass out to the sides of the rear enclosure rather than back at the driver. Also, longer frequency acoustic energy will just follow the path of least resistance toward a vent somewhere without much regard for the shapes involved. So, where's the vent?

By the looks of it, sound, or maybe better expressed, pressure, is vented back into the ear chamber at the edges of the baffle plate. Though out of focus, in the below picture you can see the stainless steel acoustic mesh screen of the baffle plate vent highlighted with a red circle.

And here you can see the other side of the mesh vent, again out of focus and highlighted with a red circle, on the inside of the ear cup on the baffle plate. These vents form a circle around the entire baffle plate.

The Sennheiser representative said Axel claims these mesh panels have important acoustic impedance properties the tune the venting. My take is that a venting system of this type may indeed damp lower frequency resonances often found in sealed headphones, but runs the risk of low frequency cancelation by adding the acoustic energy from the rear of the driver to that of the front of the driver. However, the folks at Sennheiser are no doubt well aware of how these things work, and have likely carefully tuned these vents to work in concert to critically damp the acoustic response as a whole. Like I said, it sounded tight and clean to me.

I very much looking forward to listening to the finished product, it did seem fairly unlike the sound of most sealed cans in that is sounded quite coherent and even.

I point out some of the above features in the video as Wally demos the Sennheiser HD 820 for us.

View on YouTube here.