Headphone amplifier and audio-image enhancer

The HeadRoom AirHead sounds very nice

I don't mean to be an audio geek. I blame Steve Jobs for it. I was perfectly happy just being a coder and sysadmin geek. But, you see, an OS X laptop is really good for a Unix coder geek. And it's hard or maybe impossible to have an OS X machine and not subsequently be sucked into getting a cool iPod. I call it the iPod tax.

That's the beginning.

It seems that in order to sound at all good, earbuds need to fit your ears correctly. The earbuds that ship with the iPod sound somewhere between OK and lousy depending how they fit your ears. It seems that my ears (more exactly, ear canals) are bigger than average (no doubt to match my big mouth) so I fall on the lousy end of that spectrum. But that's easily remedied by buying a pretty-inexpensive set of headphones. And maybe a not-so-inexpensive set of earbuds that sound very good indeed and block a lot of external sound, for when that's desirable. And maybe a set of powered speakers since the iPod is more convenient to use than a CD changer and also sounds better through them than my unremarkable stereo sounds through its speakers. And if you're going to listen to an iPod that way, you might want a remote control.

Whew! Well, at least we're done now and can close the chapter on audio geekery.

Um, maybe not. You see, there's something called a headphone amplifier. On the face of it, that sounds like the silliest thing ever. I mean, how much power can it take to drive a pair of headphones? And wouldn't every manufacturer of something with a headphone jack put at least that much power on the jack? As it turns out, not a lot of power and, even so, no they don't. There's no shortage of headphones that require more power than is available on many headphone jacks, especially headphone jacks on portable players. Dan over at Dan's Data has a cool review of a hand-built headphone amplifier and more background on the subject.

But I don't actually have that problem. The headphones I have can easily be driven by the power available on my iPod's and iBook's headphone jacks.

"Sowhat'syerprollem?" I hear you ask. Well, it has to do with "imaging". It's like this: Almost all recordings are made with the idea that you'll listen to them using stereo speakers. With speakers, you get some crossover; you hear the left channel some with your right ear and vice-versa. Feeding the left channel only to your left ear and the right channel only to your right ear, as headphones do, is apt to make what you're listening to sound at least a little funny. The sound that OS X makes when you drop a file in the trash is an extreme example. On speakers it sounds fairly well like something bouncing between the sides of a trash basket that's in front of you. With headphones, it sounds like a ping-pong game.

A good audio-image enhancer for headphones doesn't just mix the channels. It also delays very slightly the arrival of the portion of each signal that it sends to the opposite ear, since that's what happens in real life. The appropriate delay is a small portion of a millisecond, but you still can hear it, albeit not consciously. A really good audio-image processor will also vary the mixing depending on the frequency, since that happens in real life too. There's more detail about that on HeadRoom's admirably informative site. Follow the links on the left margin ("How We Hear", etc) for the other pages of the article. HeadWize also has more on the subject.

As with many things in audio, you can take price and even, perhaps, quality to absurd heights. (That's one reason that I'm glad to be a digital geek: with bits, the engineers know when the circuit is done because the bits come out right; with analog circuits, you can spend as much time and money as you like improving the waveform just a little more.)

So I was chiefly looking for something to do audio-image enhancement. There's no important reason that it's necessary to combine the imaging function with the amplification function, but it's convenient to. And there's always the possibility that I'll want the amplification function later.

So I got a HeadRoom AirHead. Actually, I swallowed their marketing pitch and got the Total AirHead version. And it sounds very nice. When I plug my headphones into it and switch on the crossover circuit, the apparent sources of sound migrate from the sides of my head to places in front of me. Depending on what I'm listening to, the difference may be subtle, but in all cases it's significantly more pleasant in my opinion. As for amplification, the AirHead appears to be able to do plenty.

The thing sounds very good. The way it looks is, um, another story. If you put it next to an iPod, I suspect that the best thing you'd say is, "At least it's black".
AirHead photo

You can see the input from the AC adapter (sold separately) on the left of the photo, line-in at the top, a mini-plug plugged into one of the headphone output jacks on the right, and a second headphone jack unused at the bottom. It looks like the AC adapter isn't plugged all the way in, but that's as far in as it will go. The green LED indicates that it's switched on and the red one indicates when it doesn't have as much power as the volume level requires (most likely because the batteries are running low). Between them is a thumbwheel for volume.

I can't yet verify HeadRoom's claim that it will run for 40 hours on a set of batteries (it takes 4 AAAs). Indeed, I'm also not yet sure that I'll take it with me when I travel. It's just about the same size and weight as an iPod and it's not immediately clear to me that the improvement it produces would be worth carrying it with me. Clipping my iPod's case to the pouch on the back of the seat in front of me in an airliner is easy enough. I'm not sure that cabling an AirHead to it and stuffing it in there would be all that much fun. Time will have to tell on both those counts. Nevertheless, for headphone listening at home, I'm very pleased with my AirHead.

Coincidentally, Dan has a review of a related product from the same company just now on his site.

I promise that I am not going to become one of those people who think that cables need to be broken in before they will conduct electricity well.

Posted: Wed - May 19, 2004 at 03:51   Main   Category: