A better hearing aid?

Open-fit models don't block the ear canal, so some people find them more comfortable.

Hearing aids come in all shapes and sizes, and their insides have gone digital and amazingly diminutive, like so many other gadgets these days. But for all the technological pizzazz, hearing aids today have the same three basic parts as yesterday's models: a microphone that captures sound, a processor that amplifies it, and a tiny speaker. (The speaker is sometimes referred to as the receiver, a confusing bit of jargon.)

Some types of hearing aids fit all three parts into a single piece. These "in-the-ear" aids range in size, but they can be small enough to fit into the ear canal, so you can barely see them. But the size also poses problems. The smaller versions may slip out of place. The controls can be difficult to adjust. Sometimes having a hearing aid in the ear leads to a buildup of earwax.

Advantages to being behind

Behind-the-ear hearing aids are an alternative. The microphone, processor, and speaker are also usually housed together, but in a curved unit that tucks behind the ear. The amplified sound travels down a slender, hollow tube to the ear canal.

Although they might look a little old-fashioned, the behind-the-ear hearing aids have a lot of advantages. Because the components can be bigger, the behind-the-ear aids can be powerful, boosting sound by as much as 80 decibels — roughly the difference between a whisper and a car horn. They also tend to be more durable and easier to keep clean.

But the behind-the-ear design also has some drawbacks. Whether it's on stage at a rock concert or near your ear with a hearing aid, feedback occurs when the amplified sound from a speaker gets picked up by the microphone. In effect, the sound is getting recycled. To minimize feedback, behind-the-ear hearing aids have traditionally been designed with earmolds that cover the opening of the ear canal (see below). With these "closed-fit" models, the sound is directed down the ear canal so it's less likely to leak out and get picked up by the microphone, which would result in feedback.

But the earmolds do make the hearing aid conspicuous — a major disadvantage, considering that many people who might benefit from hearing aids don't get them because they worry the aids will make them look old. Many people are also bothered by the physical sensation of having a stopped-up ear.

But perhaps the biggest problem is that the earmold can make some sounds — particularly your own voice — seem hollow and strangely deeper than normal. It's as if you had plugged your ears with your fingers. The distortion happens because sound waves, some of which get conducted by the skull, get trapped behind the earmold. The earmolds have vents that help, but they don't eliminate the distortion entirely.

Open ears

Although feedback still occurs, hearing aid engineers have figured out how to reduce it with sophisticated sensors that detect and cancel it out. Better feedback control has meant that it isn't necessary to cover the ear canal to keep sound from escaping.

So virtually all the hearing aid companies make a behind-the-ear hearing aid that leaves the ear canal open. These "open-fit," or "open-canal," hearing aids still have a very small piece in the ear canal, but it lets air through and is there only to hold in place the slender tube through which sound is piped into the ear canal. In some models, these little holders resemble tiny badminton shuttlecocks made of clear, pliable plastic.

Meanwhile, the behind-the-ear components of these hearings aids have gotten slimmer and sleeker, so over all, the hearing aid is less obvious.

Reliable sales figures are hard to come by, but audiologists report that the open-fit hearing aids are extremely popular. "People love them," says Lisa Walker, an audiologist at Harvard-affiliated Brigham and Women's Hospital.

The gradual hearing loss that many people experience as they get older usually involves losing the ability to hear high-pitched sounds carried by high-frequency sound waves. Most of the current crop of open-fit hearing aids are designed for that type of hearing loss. People with hearing loss in the lower frequencies usually need more amplification, so the open-fit design wouldn't work for them — too much sound would leak out and cause feedback, notwithstanding all the advances in feedback control, according to Racheal Rush, an audiologist at a practice affiliated with Beth Israel Deaconess Medical Center, a Harvard teaching hospital.

The least expensive open-fit hearing aid costs $1,200 to $1,300, which is several hundred dollars more than the conventional behind-the-ear devices. The most expensive models cost over $2,500, but there are mid-priced models that provide sound quality comparable to those deluxe models.

Are they worth it?

By some estimates, only 20% of people who would benefit from a hearing aid wear one. Money is a big factor: Medicare and many insurance plans don't cover hearing aids, so they're one of the largest out-of-pocket medical purchases that many Americans face. And the fact is, many people do manage to get by with pretty bad hearing. They turn up the volume on the television and the radio. Often they hear just fine on the telephone.

But if there's background noise, or lots of people talking, even moderate hearing loss becomes quite noticeable. Walker says the open-fit hearing aids may be the answer for people who find themselves in those situations often: "It is the businessman's or surgeon's hearing aid."

Finding objective, reliable assessments of hearing aids is difficult, and that's no less true for this new wave of open-fit aids. Often the early clinical trials are sponsored by manufacturers. When the neutral studies do finally get off the ground, they're investigating models of hearing aids that are already out of date.

So in the hearing aid world, it's not the large study in a medical journal that determines the fate of an innovation, but sales figures. Open-fit hearing aids seem to have some advantages, but time will tell if the demand for them stays strong.