Sunday, March 06, 2016

A variable "tuning fork" with volume

Tuning forks have one job: to vibrate with a single fundamental frequency. Simple tuning forks are often troubled with some harmonics, but the overtones are typically very small in amplitude. The fundamental frequency produced by each fork is determined by its composition and physical characteristics. Most are made of aluminum, and their tone is fixed by the length of their tines.

Variable tuning forks have weights attached to the tines; the location of the weights can be adjusted. The frequency of the fork depends on the location of the weights. Such forks are okay in a pinch, but they're a bit dull for my tastes and their Q factor leaves something to be desired.

The good folks at Next Generation Science (whose corporate name is harder to find via search engine results in the NGSS era), offered an electronic tuning fork (Sound Generator) that could produce tones at 400 Hz, 600 Hz, and 800 Hz.

But wouldn't it be nice to have a small-scale, full-spectrum variable tuning fork? Perhaps you already do.

There are frequency generators aplenty available for smartphones. (I have FreqGen, but that one seems to have vanished from the iTunes Store.) What's important is that you can adjust the frequency of the output tone down to the hertz. You can turn your smartphone into a variable tuning fork easily enough. But much like a tuning fork, the smartphone's sound doesn't carry out to much of a volume. The common solution is to set the tuning fork into a resonance box.

But for the smartphone, that's where a portable speaker comes in handy. I have a Bluetooth speaker that is capable of achieving considerable volume. Once the speaker has been paired with the phone, you can unleash whatever frequency you like at volumes that can annoy people and animals for many meters all around.

I don't recommend blasting out 16,000 Hz at full volume simply because it cripples teenagers while leaving you oblivious. That's just cruel. Every time I do it, my students hate me for several minutes.

Use this newfound tool for good, not evil. It could be leveraged in a "speed of sound" type lab. I'll share my primary use for it in another post.


Bill Bradley said...

Audacity is free, cross platform software that will allow you to generate any frequencies or combinations of frequencies that you desire. It does much, much more than that and be be used for all sorts of nifty labs: ball-parking the speed of light by the pauses in Apollo astronaut conversations with Mission Control, measuring the speed of sound in different media, high precision timing of Newton's Cradles, oh, and apparently some people use it for musical things...

Dean Baird said...

I think of Audacity as an audio version of a QuickTime-like utility. It probably does a million things I've never used it for.

For my own purposes here, I was not looking for something to put on the computer. I wanted something portable that would output a pure, loud, single-frequency tone. A sound source that I could easily bring anywhere in my classroom. On which the frequency might or might not be visible to bystanders. No bulky laptop, and no wires.