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Ron Vickery's Blog

An ALD that Doubles as a Wok

That’s because it is a Wok, but more on that later. I decided to experiment with a parabolic microphone to see if it would be useful as an Assistive Listening Device (ALD). I have several microphones that I can plug into my amplified neckloop. The neckloop creates an electromagnetic field that corresponds to the sound pickup of the mic and my hearing aid and cochlear implant both have telecoils that can receive the signal. One parameter of microphones is their pickup pattern. Common mics are omni-directional, meaning they pickup from all directions. Another type is uni-directional, meaning they pick up from just one direction, but there are varying degrees of directionality. The third pattern is “noise canceling” or “close speaking”. They only pick up just a few inches from the front. The parabolic mic is just an omni but it is mounted at the focus of a parabolic dish. Because of the dish, the arrangement becomes a “long distance” or “far field” mic. I’m not really interested in the long distance aspect of it, but if it would allow “on-mike” sounds from a distance of about 10 feet that would be great. People are not usually more than 10 feet away in social settings.

Parabolic Mic plugged into my Amplified Neckloop
Parabolic Mic plugged into my Amplified Neckloop

You may see parabolic mics at football games on TV. From the sidelines the mic can pick up the quarterback calls even with 40,000 fans in the stadium all yelling. So I thought such a mic might be good in a noisy restaurant where we want to pick up the speech of our dinner partner and exclude other sounds.

Professional mics are expensive though, so I am trying to make my own. First I went to Home Depot to find a suitable reflector and I asked if they had any parabolas. The clerk vaguely remembered from high school what a parabola is but he didn’t think they had any. He asked someone else and I explained to him that the shape of a parabola follows a mathematical formula and the curve could extend to infinity. He assured me that if they had any parabolas, they wouldn’t be that big. Next I went to Walmart and I found an approximation to a parabola in the form of a cooking utensil called a Wok. I made a mounting bar to hold the mic at the focus. Since the wok is not really a parabola, there is not a clearly defined focal point. I can buy real parabolic dishes from scientific suppliers that would have a better focus and I may do that.

My conclusion is that my parabolic mic is highly directional. The first thing I noticed was how quiet the sound was even with the gain on my amplified neckloop all the way up. I have demo’ed it to two friends (see below) and we were able to listen from a distance of about 20 to 30 feet. That was outdoors so there was no conflicting talking from other people, such as in a restaurant. I will try the restaurant environment when a good opportunity arises. Someday I may perform testing to produce a polar pickup pattern to verify the directionality. So, performance-wise, it would be a good ALD, but it is too large and cumbersome to serve as a personal ALD. It could have application in a conference room or live theater. Very big parabolic mics could be built into the environment in a way that they are unobtrusive, and feed a sound system and/or a wide area assistive listening system, such as an induction loop.

My mic mounting arrangement did not alter the Wok in any way, so it could still be used as a cooking utensil. Now I need to learn what I can cook in my Wok.

Deborah Marcus
Deborah Marcus
Steve Barber
Steve Barber
Close up view of the mic holder
Close up view of the mic holder
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My first post

I made a crystal radio when I was a kid about 11 or 12 years old, I think. Crystal radios don’t have a power supply. They get enough energy from the electromagnetic radio waves to produce sound in headphones. But they need a strong signal and a good antenna to get enough energy. I mounted one of my crystal radios on my bike, thinking I could ride about town and listen. I was disappointed because a moving bike couldn’t have a good enough antenna. I could hear a station if I rode my bike to the transmitter and parked about 100 yards from the transmitting antenna.

That interest in crystal radios got me started in electronics and I dreamed of becoming a “ham” with my own FCC license. But my interest shifted to audio and high-fidelity. I never was a musician but I enjoy listening. It became my goal to someday have the world’s best audio playback system. I got sidetracked on that goal because I soon had to buy refrigerators, washing machines, and such.

Even though I had to buy household things, I managed to have a decent audio system. However, my enjoyment of music got a serious setback when I experienced sudden hearing loss. It was not only music, but normal conversation was seriously impaired. After I got over the shock of sudden hearing loss, which took several years, I learned there were some things that worked with hearing aids that would be of benefit to me. These things were very simple amplifiers, microphones, wireless devices, etc. We nowadays call those kind of things Assistive Listening Devices, or ALD for short. The ALD industry has matured and now there are very sophisticated devices available. It is now my goal to design really simple things that are useful. So that is what this blog will be about – simple devices that other hobbyists can make or maybe improve upon.

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