Sub audio Infrasound

[lvictorlucas]

Here are some ideas for the person that was interested in building a sub audio infrasound system at Sundays meeting. I plan on being at the lab on Wednesday so we can discuss your progress.

A system typically consists of three primary functions although other purely mechanical [elastic band (guitar), plate (drum) or volume (whistle)] or other more exotic configurations are possible.

These three functions are:
1) Oscillator
2) Amplifier
3) Speaker

The oscillator produces a tone which determines the frequency. Audio is typically considered to start at 20Hz (cycles per second) and go to 20KHz (20,000Hz). The actual high frequency which can be heard usually decreases with age. Below about 10Hz people feel not hear the sound. From your question I assume you are just interested in a fixed frequency sine wave. It is easy to modify the circuit to make the frequency adjustable by replacing a resistor with a potentiometer. Since you want to use this project to learn soldering you next choice will probably be to select either discrete transistors or an operational amplifier (op amp) design. See some of the links I have listed below.

Here is a link to a simple one transistor you might select:

http://www.zen22142.zen.co.uk/Circuits/T...lf_osc.htm

This link shows some schematics to get an idea of the number of parts required for various designs:

https://www.google.com/search?q=low+freq...d=0CEgQsAQ

The amplifier increases the power of the tone. Low frequencies take a lot more power than higher frequencies for reasons I'll let you lookup. The basic choices are power transistors, integrated amplifier module or a used subwoofer amplifier. Just be sure it is designed of operation far below 20Hz. The subwoofer in the lab would be good until you verify (debug) your oscillator.

The speaker converts the electrical power to sound in air. A large used subwoofer is probably the easiest way to go. Many also combine this with a low frequency power amplifier like the one in the lab. You could build the speaker yourself but I suggest you start with the one in the lab. A few years ago the TV show Urban Myths built one to blow out the windows in a car. I suggest you look it up on line. Another method is to directly generate the pressure wave (tone) in air by using compressed air and a solenoid valve but this is going to be more expensive unless you have access to the parts. That configuration also requires a muffler to remove the high frequency hiss. An electrical high pass filter only requires a non-polarized capacitor out of an old air conditioner and a resistor.

Here are some links I quickly found to get you started:

http://en.wikipedia.org/wiki/Infrasound

http://www.unexplained-mysteries.com/for...pic=228327

http://boingboing.net/2010/11/08/testing...und-t.html

http://www.forteantimes.com/features/art...apons.html

http://www.electroniq.net/audio/simple-a...lator.html

http://www.brighthubengineering.com/diy-...t-effects/

http://datasheets.maximintegrated.com/en/ds/MAX038.pdf

http://www.linear.com/product/LTC6991

http://www.instructables.com/id/Build-an...Subwoofer/