Hearing aid design

The $4000 aids are not that much better than the $400 aids I use. My wife has the $4000 variety, and I have the $400 variety. Unless your hearing is REALLY bad, the $400 units are fine. I do not get any $$ or anything else for recommending them, but check these out at HearingHelpExpress.com. I have the Earmate4000 model, very happy with them for the past 5 years. Before, I could rub my fingers together right by either ear and hear nothing, with the Earmates, when I rub my fingers together, I can hear the scraping sounds. That is how I double-check that they are working.

Thirty years ago, good Starkey aids cost $2K. So $4K is a relatively good deal.

See below. But I haven't seen a pocket aid since my GGma's, 40+ years ago.

Depends on the make and model. It could have been.

I used to hang out with hearing aid types. There was (or maybe still is) a company that designed transducers for hearing aids, Knowles Electronics:

dead-at-83.html

One of his employees, Mead Killion, was interested in designing aids that compensated for frequency loss, with the aim of producing high fidelity hearing aids. (Scroll down till you get his doctoral dissertation.)

That was thirty years ago, so I imagine things have come a long way.

One problem at that time, at least, was unlimited high frequency response of the microphone. You couldn't talk to my HOH boss when we got to the end of any hallway, because his hearing aids automatically stopped amplifying when they got close to the ultrasonic motion detectors, when the sound output overloaded them.

55DB is a LOT. I think your biggest issues are gonna be AGC and compression so you stay within the P-P output range of your amp...and what's left of your ears. Don't think that a linear amp is gonna be satisfactory.

Shouldn't be too hard to simulate. Plug the microphone and earplug into your sound card. Google should find you a program that can filter the sound.

I'd like to add a note here: Any honorably discharged US military Veteran should be able to get a hearing aid from the VA at little or no cost.

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You can't have a sense of humor, if you have no sense.

I'm not so sure. I think it has to be a service related disability to qualify, not just age related:

Still, it's worth a try.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Correct. It will. I don't know much about hearing aids except that they're expensive. When an impoverished friend volunteered me to build for her a hearing aid, I started to learn fast. We decided that the in-the-ear and behind-the-ear variety were mostly made for convenience and appearance. A comfortable pair of earphones would be sufficient for most purposes. I collected some assorted electret microphones, an assortment of earphones, and an Alesis stereo equalizer. Something like this but older:

The plan was for her to play some music, talk radio, and recorded conversations through her hi-fi, while adjusting the equalizer, and trying various combinations of mic and earphone.

Well, that was the plan. The first thing I discovered was that she needed about a 30dB dynamic range to cover all the important frequencies. Small earphones were horrible. Earphones that screwed in the ear were best, but she didn't like those. I settled on a pair of Sennheiser over the hear headphones.

The mic had a similar problem. Electret mics pickup all kinds of odd garbage when near appliances, computers, transformers, etc. The are also somewhat omni directional, which means they pickup unwanted background noise. I crafted a directional mic, and applied a

300-4000Hz filter. Never mind the music.

The graphic equalizer curve looked very much like her hearing sensitivity graph. Both ears turned out to be roughly the same, so I setup both channels in series to get enough adjustment range to deal with her approx 30dB loss. I also tried and discarded a compressor, which only brought up the background noise level.

I then build a rather oversized amplifier, with the proper frequency and gain curves. It worked fairly well at meetings, quiet conversations, TV, radio, and telephone. It didn't work so well in areas where there was considerable background noise or echo, such as bus stations, in crowds, shopping centers, and near roadways.

Bottom line is that it can be done, but you'll need to make some compromises and concessions, such as the physical size.

Good luck. The local audiologist claimed that it was against California law to recycle hearing aids. I never verified this. Note that it's also illegal to sell throw-away (non-replaceable battery) type hearing aids such as SongBird:

Ouch. You'll never make it. 55dB of gain between a mic and a nearby speaker is going to create a feedback problem. If you can isolate the mic from the speaker, you might have a chance. Note that a normal hearing response is NOT flat, and that you may not need to fully compensate. Also, if you can live with just voice, and ignore music, a frequency response that quits at 3KHz should be sufficient. That's what you get on a telephone.

The one I built had a rubber ducky toy on top of the headset band, with the mic inside. Besides being cute, it also decoupled the mechanical vibrations from the mic.

I'll see if I can find the docs and photos. However, I suspect they're gone as the relative pillaged everything from her apartment when she died. I didn't keep copies.

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Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Also, you might consider doing this digitally, with a DSP development system. Digitize the mic audio as early as possible. Then you can filter, limit, noise limit, and tweak the curve quite easily. You can also Bode shift the frequency slightly (i.e. about 1Hz) to prevent feedback.

(From 1991, but still interesting).

Student thesis on the design. Might be a good start.

Google for "dsp hearing aid development".

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Not too many years ago (maybe 4-5), I found some cheap hearing "amplifiers" or similarly labeled devices in a Dollar General store (maybe $5-10).

These weren't sophisticated obviously, but something similar could be used for a basic building/experimenting sample. They were made in a similar overall appearance to those older behind-the-ear, tapered, little curved box.. which also held a couple of 357 type batteries and had a tube that had a tip which fit into the ear canal opening.

Upon inspection, they turned out to be just another looky-like another product that the Chinese are so famously known for. The reason I say this (again) is because there weren't even any holes in the plastic directly in front of the microphone. So, I drilled some holes, and they did amplify sounds (nearly all sounds).. but probably not very useful, in general, to someone with hearing loss.

I mention them because they may be useful as a building block for a more sophisticated amp system, even if the sophisticated DSP or other circuitry may not fit in the little behind-the-ear housing (utilizing maybe a separate thin enclosure clipped to collar or clothing.

I built a hobby grade pocket-type hearing amp kit in the 60s, and the trouble with having the mic in the pocket is that the noise of the shirt pocket fabric moving over/rubbing against the mic opening is also amplified.

So.. unless someone has a Jamaican hair style with small braids and beads on them (don't know the actaul name for that style).. having the mic near the ear is a much better plan, IMO (may even provide some directional sensitivity when both ears are using separate devices/amplifiers).

I've never used any Bluetooth devices, so I wouldn't have a clue as to how useful those types of devices may be, as far as experimenting/modifying for a practical hearing device.

Some components from cellphone headsets may be useful, but be aware that those products are generally made with the cheapest components available and essentially no quality checks.. the cables are fragile and very easily damaged by normal use (basically throw-away products, like most other inexpensive gear these days).

-- Cheers, WB .............

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A friend of mine, who while in the military spent years in the Engne room and as a result lost his hearing at all the bearing frequencies - he had 'holes' in his hearing. Don't know why, but even when he asked; he was never compensated, nor outfitted for any correction electronics. He was essentially told, tough. His lack of feedback while he talked was impressive. As he talked to you, he was so loud that you felt like a cartoon character with your hair straight back form the blast.

ex-Hearing Aid employees told me that the ear is a really unusual organ. They said that there are more nerves going FROM the brain to the ear than there are nerves going from the ear TO the brain. Something about the way the ear works, has a lot of muscles that tighten those hairs etc. Seems people hear more from what it takes to 'adjust' those muscles than from just the vibration sensation alone.

It depends more on your income. I know a lot of Veterans with hearing aids and not all are disabled. Military retirees fall under 'Tricare For Life', but are still served by the VA medical system and I know veterans who get hearing aids & the batteries from the VA. the local VA clinic has a full time hearing aid tech in the Prosthetics department. The first step is to dig out your DD214 or other discharge papers and apply for a VA medical card, if you qualify. The application form is on the http:

website. or you can go to any 'Veteran's Service Officer' for the form and help to fill it out. You can request a replacement DD214 from the records office, if needed.

Start here to see if you are eligible for VA care:

To apply, go here:

You can download the form and fill it out from here:

Then you mail it to your closest VA clinic.

You can use this form to request a replacement DD214 or other discharge papers. You can also request your entire military file, or any part you need.

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You can't have a sense of humor, if you have no sense.

How about $12.99 for one from HF?

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You can't have a sense of humor, if you have no sense.

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I would recommend the OP start with the HF aids and see if they help, it's almost worth the price just for the 3 included batteries.

You can get 6 LR44 at Dollar Tree for a dollar. The SR44 are the expensive version.

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You can't have a sense of humor, if you have no sense.

Expensive? I got tired of overpaying for button batteries and decided to stock up. I was shocked at how cheap they were from China:

50 batteries for about $3.00 including shipping.

I bought both SR44 (silver-oxide) and LR44 (alkaline) cells. For micrometers and instruments, the SR44 batteries maintains a higher voltage over a longer time than the LR44.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

That would be a good start, but probably won't work. The mic is omnidirectional and will tend to pickup undesired noise from odd directions. The mic really needs to be somewhat directional. The human brain does a great job of "tuning out" background noises and distractions. However, when using a hearing aid, that mechanism fails when dealing with mono amplification:

I don't think there's enough space inside to build much more than a few stages of analog filtering. I used a passive filter approximation that required three small pot cores connected to the amplifier output. I didn't want the filter introducing any additional noise, which was what happened when I filtered at the mic input. It also had the advantage of literally plugging in between the amplifier and the earphone, which allowed me to juggle amps along with mics and ep's. However, with 55dB of expected range, the amplifier will not have enough headroom to produce any usable output, and will probably clip badly. Still the claimed 50dB gain might be enough to make it work adequately.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

That's great if you can use all of them before they go bad. I've replaced two LR44s in the last 18 months. China is days or weeks for delivery. Dollar Tree is next to one of the grocery stores I use. i can have them in about five minutes if I run out, or when what's left of a card die.

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You can't have a sense of humor, if you have no sense.

My guess is that I'll consume about 20 per year, mostly in small flashlights, remotes, keyfobs, etc. I gave away a mess of them to various friends. I think I have about 80 of each in the fridge.

He notes that the self discharge rate is not signifigant. Maybe not.

The LR44 has a shelf life of about 10 years. Silver-oxide has a 5 year shelf life:

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Even with those numbers, I'm better off buying a half dozen at a time. Unless my health improves to were I can spend more than an hour or two a week in my shop.

--
You can't have a sense of humor, if you have no sense.

I'm embarrassed to admit that the Harbor Freight one for 12.00 really intrigues me. It says that it is tone, (whatever that means) and volume adjustable. I just wonder if it could possibly have some kind of a high frequency pre emphasis circuit in it. And since I haven't been able to find my father's old ones around here yet buying this thing might prove to be an interesting experiment, or a waste of

12.00, plus S& H for a worthless POS). Well it's not 1200.00... Lenny