The Accessorizing AirHead

Part 2: The full scoop

The theme for the past month of my life seems to lateness. My day job has been consuming almost every minute of my time, and as a result many things have been getting pushed back. I paid all my bills late, which I know from past experience will result in a stunning array of penalties next month. I originally planned on seeing The Phantom Menace right after it was released. No chance of that; I barely managed to wedge a viewing at all, and that was a full three weeks after it opened. The article I originally intended to run in this space for July, about upgrading the Radio Shack Optimus Pro X5 speakers, remains far from completion. That project has turned into something considerably more difficult than I had expected when I put the original article together back in October, and I apologize to any readers who have been disappointed by this. It remains at least three months away at this point. During that column, I also tacked on an addendum about the HeadRoom AirHead, which I first mentioned over a year ago in this space. HeadRoom has been suffering from their own delays. Hold-ups have included supply-chain issues, some electronics-design problems, and a complete case redesign. Unsurprisingly considering how the last few weeks have going, I'm writing this column late, but that delay has left me with enough time to put a new production AirHead through its paces. Was it worth the wait? As always, that really depends on what you were expecting.

The AirHead is the smallest and least expensive headphone amplifier HeadRoom has ever produced. Measuring 2.75" wide, 4.5" long, and about 1" high, the $179 amplifier weighs a bit over four ounces when loaded with its two AA batteries. Headphone mini-jacks are used for the input and output to the unit, and a short cable is included for connection to a typical portable CD player or other unit with a mini-jack line output. The volume control is a small wheel, and two switches control the power and the HeadRoom processing. Unlike HeadRoom's other amps, with the AirHead you can't separately adjust the HeadRoom processing and high-frequency filter While being able to adjust both is nice, after the novelty wore off I never found myself adjusting those two separately on the other amps, so I don't miss the capability here. There's also a 5V input to run the unit off an external power supply.

The power supply is a good place to start because that's a critical design point. A regular AA, C, or D battery outputs a little over 1.5V of power when fresh. The AirHead uses two of these, and this means the unit gets 3V coming in. The amplifier circuitry itself (see HeadRoom's guided tour for details) runs off a 10V supply internally, so an AC-coupled DC-DC converter is used to step the voltage up. Other HeadRoom amplifiers use a +/-15V power supply and are DC coupled to a power source of at least 6V. In practice, what this means is that the less beefy AirHead power circuitry is considerably more susceptible to noise, particularly of the dreaded common-mode radio-frequency type. Many audio products, including portable CD players, spew common-mode RF at any component they are attached to. With a high-voltage power supply, you can reject much of this noise. With a 10V supply running from 3V worth of batteries, that's really tough to do. How much this will impact listening with the AirHead depends on numerous external factors, the first of which is your source. Since the package I got from HeadRoom included a new CD player, let's take a look at that first.

Panasonic SL-SX300

My first Fringe column started with a look at the Panasonic SL-S320 portable CD player. That's been long discontinued. HeadRoom included a more recent player, the SL-SX300, in the package they sent me. This also appears to be a discontinued model, but it's worth talking about anyway as it showcases the progress that's been made in these portables since I last looked into them. To start, the line output sounds considerably better. Playing "A Rock for the Forgotten" from David + David's Boomtown [A&M cd5134/dx729], I was initially struck by a much fuller and better-controlled bass line. Everything about the sound is richer and more refined, with no downside that I could hear. Inexpensive DACs just keep getting better.

With the older SL-S320, I noted a pretty dramatic loss in sound quality when engaging the anti-shock mechanism. The newer "Anti-Shock Memory II" system in the SL-S320 is considerably more transparent, and I'm hard-pressed to find any flaws in how it sounds. I believe I heard an occasional rhythmic noise that modulated when the system was really working hard, like when I was walking. But it was certainly a low-level kind of distraction, not something to be seriously concerned about.

The SL-S320, while fairly shock resistant, could be made to skip without too much effort. Either fast walking or climbing stairs would cause the player to lose track of the music occasionally. And I found it very difficult to rely upon when using the treadmill at the gym. No matter how I attached the player to the treadmill, once I got around 6MPH or so, the player would skip enough to be useless. Now, if you can tweak the unit you run on, it's possible to work around that. One gym I visit, Tropical Shade in Hoboken, has attached plastic shoe boxes to some of their treadmills. They punch four holes in the box and run plastic wire ties through them and around the display unit. The intended application of this addition is to store your keys, wallet, or other such accessories that can get in the way of your running. I found a box attached this way also provided enough decoupling from the vibration that the CD player would run without skipping, a welcome change.

All of this is totally unnecessary with the newer SL-SX300. Even with the player haphazardly attached to the treadmill, I was never able to get it to skip. Earlier today I set my 229 pounds jogging at a 9MPH sprint, and I had to stop before the CD player did (that's about 90 seconds for me). Similarly, neither walking nor climbing the five flights of stairs leading to my apartment resulted in a single interruption in the music. Panasonic claims their ASM II contains "a series of error correction chips which virtually eliminate skipping caused by horizontal shocks and knocks," and my testing agrees. They claim their more expensive SL-SW505J model will even support regular jogging when attached to your body correctly. I had been toying for a while now with Minidisk- and MP3-based portables because I found CD units couldn't quite keep up even with my workout regime. Now that I see what the newer models are capable of, I find zero reasons to accept anything less than CD-quality sound from a portable. Unless your workout involves fairly serious running outside, you should be able to find a CD portable that can keep up with you for a reasonable amount of money. Panasonic players with ASM II start at $60.

X-rated demo music

There is one aspect of performance where you might prefer the older Panasonic player, and it relates to a serious concern with the AirHead amplifier: noise. To get a handle on what I was hearing, I made a test CD of digital silence with CoolEdit and played that back with many combinations of equipment. This is more difficult to deal with than just pausing regular music, because some players do fancy tricks to reduce noise when paused. My second test case was the Mark Snow musical score from the X-Files movie [Elektra 62217-2]. I'm not a fan of the show and haven't seen the movie, but hearing this great symphonic work once convinced me to buy it. The music has fantastic dynamics, pushes the frequency extremes, and is very challenging demo material. It also has lots of dead silent parts that let me hear what's going on when the music stops for a moment.

There are two basic types of noise I've suffered with from the AirHead. I've dubbed them "the buzz" and "the tuning." Of the two, the buzz is the most annoying. With the Etymotic Research ER-4S headphones in particular, moving the headphone cord around to a spot where it cuts across the right kind of electromagnetic field gives a low-level hum and buzz that you can easily pick up during the digital silence. In my bedroom, sitting in front of my bank of three computers, there are lots of positions I can adjust the headphone cable to where I get a little bit of buzz, in a fashion that sounds like feedback. The gym is the worst spot of all. When sitting on the LifeCycle there, I'm in electromagnetic hell. Florescent lights, two neon signs right behind me, the cycles themselves, and other random electronics all radiate my body when I'm trying to get healthier. The buzzing in the AirHead while sitting there with the Etymotic phones can be a bit obtrusive because they cut out the noise of the cycle and other background sounds.

This problem, while not exclusive to the ER-4S headphones, is most prevalent with them. Listening with my old Sennheiser HD490 headphones instead gives considerably less buzz, to the point where it's only a tiny bit noticeable with silence and almost never audible over music. With Beyerdynamic DT250 headphones, it's a bit worse than with the Sennheisers. I can just make the buzz out with silence, but it's extremely tough to pick it out with music.

The tuning noise, which was a more serious problem with earlier revisions of the AirHead, is a less troublesome concern with the current production. With the volume control on the unit turned all the way up, a constant background hiss will sometimes resolve into a radio station. Again, this is most obvious with the Etymotic phones. Under the worst conditions and playing music, I'd characterize this hiss and radio-tuning garbage as being about as obtrusive as the background hiss you get with an average analog recording from the mid-'80s, played on CD. Yes, you can hear it during the quiet parts, but most of the time it's lost. The radio-tuning noise seems very dependent on where you live. Returning to my noisy bedroom, when I look out the window I see the Empire State Building very clearly across the Hudson. Given the radio output from that tower, I suspect I'm about the worst possible test case for picking up stray radio reception. Sadly, switching from the Panasonic SL-S320 to the SX-S300 reverses some of the progress HeadRoom has made on this front, as the newer unit suffers more from the tuning noise.

Now, none of these problems are 100% specific to the AirHead. Plugging the Beyerdynamic phones directly into the SX-S300 headphone jack, I get a bit of the buzz with the volume turned all the way up (a volume the player can't even come close to playing the headphones cleanly at with music). There's no tuning noise. With the Etymotics and the CD player headphone output, I get a little bit of the tuning noise at the top end of the volume range. It gets considerable buzz as well, going up to what I'd characterize as a medium volume, which is a touch quieter than the slightly louder buzz the AirHead can give. Using the Cosmic HeadRoom amplifier, I can't get any buzz with any headphones. There is a very low-level hiss that's audible at higher volumes.

It's got baggage

Spending so much time listening to noise is really boring. It's more fun to talk about bags. HeadRoom is producing a new custom-made bag to hold the AirHead. It's called, unsurprisingly, the AirBag. Normally a $49.95 add-on, at the moment a promotion includes one with every AirHead purchase. There's plenty of space for a CD portable, the AirHead, and a hole in the bag routes the connecting cable included with the amp. The bag comes with five double-sided CD slipcases that fit behind the player, which makes for (firing up Excel) ten discs of music you can keep there.

"Airbag" is also the title of the first track of Radiohead's 1997 release, OK Computer [Capitol 7243 8 55229 2 5]. I had originally assumed the extreme praise of that CD from Radiohead fans couldn't possible be justified, but after hearing how great the music and the recording are, I've become one of the converted. Computer really showcases how effective the HeadRoom products can be. When I listen to tracks like "Karma Police" using the SL-SX300's built-in headphone amplifier, the sound is unpleasant. Even at what I consider a moderate volume with the Etymotic headphones, the amplifier distorts and breaks up. And at any volume there is a layer of grunge on top of the music that I really can't bear to hear. Switching to the AirHead gives three distinct classes of improvement. First, the volume can go up a lot higher. Second, the amplification is clean and robust, rarely running out of steam even on demanding bass transients. Third, engaging the HeadRoom processing gives an amazing improvement in how the music images. With this recording, the edges of the soundstage actually moved outside of my head a little bit. The wide panorama of sound, with instruments localized all over the place, is a welcome improvement over the left/right blob of music you get with regular headphones. For a really exaggerated listen to the HeadRoom process, try the version of "Solsbury Hill" from Peter Gabriel's Shaking the Tree collection [Geffen 9 24326-2] and listen to the difference in how the vocals waver, starting with the second chorus and alternating between regular stereo and HeadRoom-processed stereo.

Marillion's debut album, Script for a Jester's Tear [EMI 7243 8 57865 2 5], was totally remastered with fantastic results a few years ago. But all that's wasted on you if you're listening through a normal portable-CD-player headphone output. The dynamics on songs like "He Knows You Know" are so constrained it's barely worth listening to. Switch to the AirHead and the band explodes out at you in comparison. Just as impressive is what happens to the drums when the HeadRoom processing is turned on. With regular stereo headphones, you hear some sort of echo on the trailing edge of the drum snap. Engage the processing, and this clearly resolves -- it's obviously the sonic signature of the room the drums were recorded in. What does moving up to the considerably more expensive Cosmic HeadRoom buy you? A bit more low-level resolution and a quieter noise floor are the main two things. You also get extra power for higher volumes along with a somewhat more aggressive treble, which can be viewed as a problem depending on how the rest of your portable system is balanced.

During one conversation with Todd at HeadRoom, I asked what he suggests as material that really shows off what the Cosmic is better at. Piano was his first response, so I pulled out the last piece of piano music I've heard part of live, George Winston's Autumn [Windham Hill WD-1012]. Sure enough, during the opening track "Colors/Dance," the Cosmic really nails the attack on the leading edge when Winston strikes the piano keys. The AirHead doesn't do nearly as good of a job handling that difficult transient, leaving you with less of a hard edge and more with a fuzzy note. Interestingly enough, the Cosmic makes one aspect of this 1980 recording worse -- the CD is loaded with its own recording hiss, which the more expensive amp throws right in your face with the ER4S headphones. This hiss easily dwarves the tuning noise and buzz the AirHead sometimes injects. So if you're used to dealing with less-than-pristine recordings, the noise from the new little amp should be of lower volume than what you already experience.

The AirHead is a product borne of compromise. The constraints of making a portable product that's small, very lightweight, and reasonably priced has resulted in some trade-offs in overall sound quality and quietness. Regardless, the considerable improvements the HeadRoom processing and better amplification give makes it just about impossible for me to go back to using my CD player's built-in headphone jack. My current favorite traveling system is built around the Etymotic ER-4S headphones, due to their low weight and extreme portability. The AirHead's performance with those headphones makes for a vast improvement over what I was getting out of the Panasonic players by themselves, even if the HeadRoom amp can be a bit noisier under some conditions. I certainly like the whole AirHead system substantially more than the older portable HeadRoom products like the Supreme and the Cosmic, which were just plain too heavy and bulky to be useful to me as portables. The amplification improvement is big enough that I'd prefer a combination of the AirHead and inexpensive headphones (i.e., the Grado SR-80) over just getting more expensive headphones (like Sennheiser HD600) and using a regular portable headphone jack to drive them. When you're trying to cram your entire music system into a little bag you take with you everywhere, your musical expectations should be reasonable. If you see me wandering on a train or to the gym, odds are good I'll be carrying an AirBag and listening with an AirHead. Odds are also good that I'm late for something, and that hectic lifestyle really makes me appreciate the kind of high-quality tunes on the move HeadRoom's products and advice enable.

...Greg Smith
gregs@soundstage.com

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