AudioQuest Reveals Upcoming Headphone: The NightHawk
I first heard of this project coming along about a year ago when I chatted with Skylar Gray (AudioQuest's chief designer on the project) at CES. I also got a personal guided tour of the NightHawk in it's most current iteration at the time a month ago at CanJam@RMAF. Astonishing then, and now, is how much innovation Skylar has managed to pack into this new headphone design. Much of it is mentioned on their NightHawk launch site, but I thought I'd take a few moments to relay my understanding of some of these design features. So, open another tab to their site and I'll talk you through what I know, and what I'd like to know more about, regarding this very interesting headphone.
Cruise down the page 'til you get to the design section and the first paragraph you get to is about Liquid Wood. Here's a good article about it. Basically, Liquid Wood is a material made principally of Lignin, one of the component materials in the cell walls of wood and a waste by-product of paper manufacture. Turns out, this material can be used to make a product that acts pretty much like plastic in the injection molding process. I don't know if this is the exact material used by AudioQuest, but this Wiki page on Arboform shows a material with some pretty terrific properties. None of the sources I found, however, compared Liquid Wood to real wood in terms of their acoustic properties.
Is wood a good material for headphones? Sure, there's been some good wood headphones. Is plastic a good material for headphones? Sure, the trick is good design and using some of the excellent forms of plastics. Is Liquid Wood a good material for headphones? I have no idea. It's probably a material as much like plastic, or maybe more, than it is like wood. It seems to me that it might be a perfectly legitimate choice if designed well. All I can tell you is the material looks pretty cool, and when I tapped the NightHawk with my fingers it felt and sounded pretty dead. We'll see.
In the photo above, the four spars radiating from the central ring outward to the headband bail are a rubbery material and used to suspend the ear capsule and allow it to pivot freely and self-adjust to the head. I don't recall ever seeing anything like this on a headphone before, and it seems like a damned good idea. When I tried the NightHawk prototypes on my head they did seem to fit nicely on my ears. I'm thinking this is a pretty cool innovation.
I'm actually more concerned with the headband tension. Headbands with elastic tensioning mechanisms are tricky to set appropriately.
Not much to comment on here except that it's nice to see what looks like a 45 degree plug at the end of the cable. It's AudioQuest, so I'm sure the cable will be pretty good.
Biocellulose diaphragms have been around a long time in the headphone world. The venerable Sony R10 had them, as did/does the Denon AH-D5000 and 7000, Fostex TH-900, and B&W P7, among many others. Many factors go into a good sounding headphone, and generalizing about diaphragm material is a bit off the mark, but I would say that biocellulose driver headphones tend to sound pretty good. Theoretically, the advantage of this type of driver diaphragm is that it's somewhat stiffer and less likely to deform resulting in less likelihood of modal break-up than thinner plastic diaphragms. Of course, they're heavier than plastic diaphragms and need a stronger motor. All-in-all, I take this as a good sign.
In the photo above towards the bottom left you can see a cross section of the NightHawk's motor. The top pole piece has two protrusions aligned to straddle the voice coil in it's resting position. This has the effect of making the magnetic field slightly stronger as the voice coil makes excursions away from the resting position. In the central resting position it takes very little effort to move the diaphragm, but as you move away from the central position, the surround at the edge of the diaphragm begins to resist further movement. The further you move the diaphragm from the central position, them more the surround resists further movement. The intention of a split gap motor is to make it stronger as the diaphragm moves away from the central position to counteract the increasing surround resistance. Okay, that sounds pretty reasonable. If this works, it may show up as lower distortion measurements in the bass.
Balanced Equitangential Airflow
That's a mouthful! Again, in the photo above, but to the right side, you see a cross section of a hole behind the outer part of the diaphragm (torus). These are venting holes that allow sound to escape from the back of the driver. The venting of air from the back of the driver through it's housing is a very important part of the acoustic design of the headphones, and is critical for proper diaphragm damping. Driver damping can make or break a pair of headphones. Skylar has focused a lot of his attention on two aspects of driver venting: the symmetry of vents around the driver, and reduction of turbulence through the vent holes.
Normally, the holes in the housing behind the driver are simple straight-walled cylinders. In the NightHawk, these holes have rounded corners like one might find on the bass port of a well made speaker which reduce chuffing and other sonic artifacts. And like with really good bass ports, the geometry isn't just a simple constant radius corner. In the case of the NightHawk the shape of these curves are 'equitagential curves', which Skylar claims is the shape best suited to reducing turbulent airflow in this application.
Now to the topic of symmetry: In the photo above is the rear of a typical headphone driver. Around the plate behind the driver torus is a series of holes to vent and damp the acoustic space behind the diaphragm. In this case you can see that this venting is not symmetrical around the driver. In one area it is completely blocked by the terminals needed to get signal to the voice coil wires. Next to that closed area is a hole with no felt over it. The remaining holes are all felt covered. My understanding of Skylar's comments is that he believes this asymmetry of acoustic impedance around the rear of the drive may lead to rocking motions of the driver. In the NightHawk, all the holes and venting behind the driver are symmetrically placed to prevent such opportunities for rocking motions. I have had headphone engineers tell me that these asymmetries don't matter much, but Skylar's view just makes good common sense to me. Headphones are tricky though, common sense might not apply, but...I still think this makes sense.
Diamond Cubic Diffusion
It seems to me that the shape and nature of the vents from the capsule housing to the outside world are one of the least likely places to run into trouble in a headphone design. But hey, if you're gonna tweak everything, then this is a thing. I actually chatted with Skylar for quite a bit of time on the possibilities of using various types of diffusers within headphones. The problem is there's not much room inside a headphone, and diffusers have a physical size relationship with the frequencies at which they work. Long story short: If you're going to build some sort of diffuser inside headphones, it's likely to work only at very high frequencies.
If the Diamond Cubic Diffuser has any real diffusing properties it's going to be at high frequencies (say above 10kHz). At lower frequencies my guess is that it's just acting as a grill. None the less, it certainly might have some ability to diffuse high-frequency energy that might otherwise end up in a resonance.
Loudspeaker Inspired Headphone Experience
This, of course, is the bit about the Liquid Wood part being designed properly to reduce vibrations in the capsule housing. I can't really comment on it because this is all about finely tuning the position of ribs and geometries that stiffen the enclosure. Also mentioned is an elsatomeric covering that further absorbs mechanical energy. Given Skylar's apparent attention to detail, I've just got to assume he put a lot of effort into this design.
Is this going to be a great headphone? Pffft. No idea. I've got to wait for a production version to show up on my head. But until then, I've got to say that this is one of the most interesting headphone developments I'm aware of at the moment, and I sure as heck can't wait to see the finished product. It's at the top of my list for CES this year.
Until then, I'll leave you with this this link to early impressions by Jude Mansilla of Head-Fi.org, and a little video of the guys who invented this Liquid Wood stuff. Seems like a very cool material to me.
Click here if you can't see the video.