The worlds Weirdest & Wackiest Inventions

reply to post by ELahrairah


I can not only hear that noise, but I can hear the ones designed to scare off cats, foxes,dogs, and rodents from houses and gardens. When at a mass market DIY store a few months back, one of the wonderful people behind the service desk was testing one of those fox repellant machines for a customer. She couldnt hear it,and was about eighteen.

I on the other hand was looking for something to break the damn thing with , because it felt like someone was drilling into my skull through my ear drums, and I wanted it to stop .... Fast.

Seriously unplesant stuff.

I played that sound for my kids just to see if they could hear it and it really upset my oldest daughter. She said there was something really wrong about it. She couldn't elaborate but while my son found it annoying, she looked downright red faced and ill. Needless to say, I shut it down quickly.

Just a little aside info for those interested in the 'mosquito' sound:

I took a look at it on a CRO and it's only a 15kHz sine wave which is quite clean and the lack of sub-harmonics etc is what makes it hard to hear. Old CRT televisions used to annoy me no end and their horizontal oscillator runs at 15.625kHz but that's somewhere between a square and asawtooth waveform which makes it rich in harmonics giving it quite a 'buzz' adding to the audibility (or 'fuzz' or you're a guitarist).

A typical human ear in 'as new' condition can hear all the way to around 20kHz and even a little higher for some (blessed or cursed is the question for them)

I did a little study decades back on ultrasonic pest repellers and the mosquito featured largely in that. As I recall, the mosquito that bites you is the pregnant female which needs a little blood for development of her eggs, all the others (males and non-pregnant females) being 'non-biters' but still annoying. Analysis of the sound the 'non-biters' (males particularly) make indicated they were somewhat higher than the slightly heavier 'biters' at around 22kHz which means 99% of humans can't hear the males but nearly everyone can hear the biting variety which are around 15-16kHz. Add to that the finding that pregnant females avoid the males like the plague and you have a recipe for a sonic mosquito repeller IE an oscillator running at 22-23kHz driving a high end tweeter and, yes, it works. You're less likely to get bitten but you're more likely to be surrounded by an orgy of non-biting 'mozzies'.

My folks had such a unit in their home for decades (ultrasonic pest repeller) and you never saw ants, spiders, silverfish, cockroaches, mosquitoes intruding in there if it was running. It upset the hell out of dogs and cats though but no human visitors knew it was running.

A crazy invention that works? - quite likely in that case.