The magic of technology


I think the armature is part of the speaker in a hearing aid? What you say sounds likely, but that’s a limitation on the frequencies it can play. What’s being discussed here is frequency lowering, so that limitation doesn’t come into it. The limitations are what can be received by the microphones, and what the circuitry can process.


I also find it possible that it’s just a limitation of the software, but I really don’t know.


Tickled rats over bat detector:

Cats have one of the widest hearing ranges, from ~20Hz to ~80,000 Hz. I often wonder what noises they are listening to when the get all still and weird. Having a bat detector would be interesting for checking that out.


Ack, these are all sciency now. The tickling looks so aggressive. In the original video there were a lot of shots of the rats chasing the hand around so that they could get more tickles, that made it more clear that they were enjoying it and not just being accosted by a giant hand. :confused:


It’s the mic.

Most hearing aid Mics roll off at 10-14KHz, which is a function of the mass of the diaphragm etc. The problem with electret mics is that as you make the diaphragm lighter, not only does it become more fragile, but you increase the effect of Brownian Motion which is heard as white noise. There’s various FG cylinder mics that would do 100Hz to 20-30Khz pretty flat with only a small peak resonance but the negatives tend to outweigh the positives, as manufacturers tend to favour flatter square TM derivatives.

The Brownian Motion contributes quite significantly to the noise of the overall hearing aid, so tech solutions to it have included HF voltage splitting to double the apparent 1.4v available and modify the mic design to move the diaphragm away from the sensor surface.

I’m wondering if the Bat detector has a few batteries in it and a higher available voltage to make better use of a 6V mic rather than one that operates at a quarter of that.


He said the bat detector uses 3 AAs and “flattens” them overnight. Maybe they’re wired in series to get more voltage?


In that case it’s 4.5v or 9.0v if they’re using the same fancy HF AC summation that some of the manufacturers now use. Or even more if you’ve got some sort of transformed or accumulator/avalanche system. That allows you to switch more volts across the electret mic input and move the mylar diaphragm away from the permanently charged surface - thereby allowing more discrete travel and more sensitivity. Also the effects of Brownian noise are mitigated against.

That’s a totally different affair than a mic for 1.4V battery that needs to last all week on a tiny MAh rated battery.


Yes, there’s definitely at least 4.5v available. Some use 9v batteries. Then there’s also the fact that no one knows what bats really sound like, so savage noise reduction is possible and no one knows the difference.

Still, it wouldn’t surprise me if there was a usable signal available from HA mics much higher than 12kHz if they were prepared to allow loss of sound quality in order to access it.


It’s just pretty redundant for speech, even music doesn’t have many listenable parts above that level. And even less worth it if you can’t reproduce that signal with your single receiver.


Look at the sets of speakers an audiophile has to get such reproduction. Now, if you could only cram all that in an ear, you’d meet your goal. :slight_smile:


There are some great custom in ear monitors musicians use. Funny enough they rarely match the price of hearing aids.


That’s just a speaker on a wire though, even the best ones are just three receivers and a couple of crossover circuits.


Not to hijack, but FYI for North Americans, Australian fruit bats are adorable and look like baby foxes (known as flying foxes).

When I moved here to Canada front aus I was so surprised at what people thought of bats. I don’t want anyone to thing @pters is…peculiar


I can assure you that there are plenty of Australians with bad attitudes towards flying foxes. But flying foxes call well into the audible range, it’s one of the major complaints about them. It’s microbats that I record, the tiny ones that eat insects.


For sure. My mum got landed on my a FF and had to get shots for it.

But over here people are literally terrified of them as some people would be of mice or huntsmen spiders. They do carry rabies and they aren’t nearly as cute a FF. I just wanted to clarify for the North Americans on this forum so they didn’t think you were crazy!


We all have our particular interests and hobbies. I find this one interesting. Particularly the device to “listen” to them.
I live in a more rural area and appreciate what bats might exist around here for their mosquito eating prowess. That and dragon flies.
Terrified? No. In the blindingly rare instance of possibly being bitten by one sure…I’m aware of the other rare possibility that they might have had rabies. They don’t all do all the time.


I’ve worn hearing aids for over 20 years and I’ve found that the key is an audiologist who will listen combined with my dedication to accurately explaining the situations where I have trouble. Sometimes, I’ve been able to happily go for years without adjustment (well, maybe just 2 years). But other times, when my hearing loss changes a bit, I need to go in every 2-3 weeks until we get it right. It’s a team effort, even with the best technology.


I found it intriguing that bats are flying around our suburbs at night, undetected. A $30 toy ultrasound detector let me find out more about one of the few types of mammal that survive around civilisation. I have a recorder set up permanently in the back yard, and (when I bother to download and check it) find I get regular visitors. Nowhere near as many as in forested areas, and way more in summer than in winter, but still regular.

In Australia we have one species, the white-striped freetail bat, that calls at about 15kHz, so younger people can hear their metallic clicks. I can barely remember being able to hear them.

As for catching things from them, yes, it’s possible, but not easy. Researchers and rescuers have to be immunised before they’re allowed to handle them, and they handle them with gloves, but not so long ago they didn’t bother, and there were rarely problems.


But enough about bats. I found this interesting article about hearing aid frequency shifting:

There’s a table on page 4 listing all the different names each manufacturer has for it - Audibility Extender, SoundRecover, Spectral iQ, Frequency Compression (special prize to Signia for that one for not letting the marketing dept choose the name), Sound Shaper, Speech Rescue.

It sounds like they all use different variations of the basic techniques, so I imagine they all sound different. People who have got used to the sound of one manufacturer’s technique would likely take a while to get used to another’s.

I will have to find out from my audiologist if I have it turned on (and whether my aids even support it). When I first got them, people’s sibilants sounded extremely harsh, like a tiny burst of white noise. A few months later, I barely notice that. It could be that that’s what everyone sounded like back before my hearing went, but I don’t think so. I’m wondering if I was hearing the results of Oticon’s “Speech Resue”.


Searching for information to confirm if my aids have frequency shifting reinforces my impression that this industry is very patronising towards its customers. I can’t find any lists of models listing their features. Only vague descriptions of how great they are. Even a search for the model and the exact name of the feature came up with nothing. Selecting aids is for audiologists, not customers?

I did find that Oticon’s “Inium” thingy (chip?) supports it (Speech Rescue), and that my aids (Ria2 Pro) contain the Inium thingy, so it’s very possible, even though it’s a badic model.

I also came across this Oticon leaning module:
I’m not sure what audience it’s aimed at. It starts off with quite basic information about hearing that audiologists would have leaned in the first week of their course, with a patronising cartoon figure looking glum at the news that they can’t understand speech well, then raising one eyebrow at the news that Oticon might have a solution, then cheering up when they hear that they do. And then later on in the module, it shows you how to enable and adjust the feature in Genie, presumably the software used to program aids, something surely exclusively for audiologists. Perhaps Oticon is patronising to audiologist too?