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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
