It’s not every day that you see something new in the world of personal stereo headphones. From the lightweight over-the-ear sets that came with the first Walkman to the white earbuds distributed with the Apple iPod, real innovation has been hard to come by. The “look” of the basic product has changed radically over the last 30 years, but the actual mechanics of turning an electrical signal into sound in your ear has remained largely unchanged… until now.

The new AirDrive headphones from InAir Technology represent a significant departure from the design of previous headphones. They do this by placing the drivers that emit sound in front of the tragus of the ear, rather than over or inside the ear canal. Sound from the AirDrive headphones is then caught, reflected, and amplified to the other parts of the human outer ear, allowing the listener to hear whatever those headphones are playing.

The potential benefits of this design are significant. Biggest on the list is hearing protection. Concentrated sound waves are not emitted directly into the ear canal, thereby significantly reducing the potential for hearing damage. Any sound can cause hearing damage if it is loud enough, that is true. The possibility that a sound produced by a personal stereo will reach that threshold is much smaller with the AirDrives than with other kinds of headphones. Another benefit is that the hearing surfaces of the ear are not blocked by the AirDrive headphones while they are in use. It is possible to hear other people and noises much more clearly than with headphones or earbuds that cover the ears. Devices that are brought to the ear (such as a phone receiver) can be used without removing the AirDrives, making tasks like answering the phone less cumbersome.

Innovation is fine, I hear you say… but do they sound good? The answer depends a lot on what you are looking for. If you use a set of AirDrives headphones with an iPod, they sound about as good, crisp, and clean as the earbuds that Apple provides — a comparable volume level. That last part turns out to be rather important, because all that hearing protection that the Airdrive design promises comes at a price: sound volume. Personal experience shows that you need to increase the volume level of a device like an iPod by about 25-30 percent in order to get a sound level comparable to that of the Apple earbuds. If you have always been concerned about the possibility of hearing damage and keep your volume levels low, this will not be a problem. If you are into the Disaster Area-like sonic experience, these headphones are not for you.

These headphones also cannot ignore the laws of physics. Lower frequency sounds generally require larger driver surface areas just to create all those longer sound waves. Since the membranes that make the sounds are both about the size of dimes, the low end response of the Airdrives has a lot left to be desired. Here again, they are not much different than the earbuds that Apple delivers, but you get those for free with the iPod and the MSRP of the Airdrives is over $50. There are other headphones with better low end response for the money.

There are also times and places where you want a personal audio device to help mask out the noise of the world around you. I personally prefer to listen to my own music collection at the gym rather than exercise to whatever it is that happens to be playing over the PA system at the moment. I look to my headphones to help cover over that music as well as the ambient background noise. The Airdrives are not well-suited to this kind of situation.

This is not to say that the AirDrives do not have their sonic advantages. The sounds produced by the AirDrives have a more interesting sense of space and dimensionality than those produced by other headphones. I assume that this occurs because more of the processing of the sound is done by the human outer ear, and the outer ear is designed to help the brain locate the sources of sound.

In all, I have to say that the AirDrives Interactive Stereo Headphones represent an interesting advance in personal listening technology. Are they for everyone? No. They will appeal to a segment of the listening public who want a safer way to get a more dimensional sound out of their personal music players.