[Elecraft] [K3] Hearing aids, meet K3

[Jim Brown]

On 8/8/2013 6:19 AM, Bob W7AVK wrote:
> Most of the recent Hearing Aids have something called T Coil or 
> similar feature.  Very popular in Europe where folks gather like 
> churches, etc. its essentially an inductive pickup. 

Yes, it is, but it has never gained traction in the US, where virtually 
all systems for the hearing impaired use RF or infrared. I've used both 
successfully in some pretty big spaces, but prefer IR for most venues.

The Achilles Heel of these systems is stray magnetic fields, which can 
add 60 Hz hum to your hearing aid. Two common sources of stray 60 Hz 
fields -- the transformers in big power supplies, and wiring errors in 
the power system, the most common of which are mis-wired outlets and 
double-blonded neutrals. Most of us have power transformers somewhere 
near our operating desk, and wiring errors are common (houses are wired 
by human beings, and we, as a species, make mistakes).  :)

Modern hearing aids are built around microphones and chips specifically 
designed for that purpose, with lots of equalization and other signal 
processing that can be tweaked to compensate for each individual's 
hearing loss. Engineers from Etymotic Research, a major manufacturer of 
both the chips and the microphones, was quite active in the Chicago 
Section of the Audio Engineering Society, and gave a couple very 
interesting presentations to our meetings about the microphones, the 
chips, and the systems as a whole. I don't know which brands of hearing 
aids use their components. About ten years ago, they hired the engineer 
from Shure who designed the very popular SM-58 mic. Last I heard, he was 
working on directional mics for them.

A well-designed hearing aid should roll off the low end on T-coil inputs 
to minimize this, but I don't know if they do or not. Perhaps someone 
who is using it (or has tried it) can comment.

Another comment. Hearing aids are very expensive in the US (I hear 
$5K-$6K being typical), and I strongly suspect that it is the result of 
limited distribution contracts between audiologists and the 
manufacturers to protect the high markups. Costco's prices are about 
half that, but they tend to be well rated, and W6OAT is VERY pleased 
with his. I also saw/heard a piece on either NPR or PBS a month or so 
ago about a guy who is developing a low cost hearing aid that he intends 
to sell in the $600 range. It's less sophisticated than the others, with 
fewer adjustments.

73, Jim K9YC