Low Frequency Science!

Ever tried blowing through cardboard tubes and found that after a certain size, the pipe becomes just too big to make a sound? As pipe diameter increases, the pressure of air required to create sound also increases.

Our answer? A 500,000 BTU propane blowtorch to rapidly heat air in a 14" diameter pipe, causing huge amounts of air to be sucked through the same way you would blow through a didgeridoo.

In open ended pipes, normal air pressure at each end acts as a reflector to air reaching either end of the pipe, causing moving air to bounce back and forth within the pipe at a certain rate, or frequency.

A high pressure zone of air moves back and forth through the pipe twice to form one wavelength. The rate at which this wavelength is repeated, as determined by the speed of sound in the medium, is the frequency of sound you hear.

In the case of this 12 foot pipe, the fundamental frequency is approximately 47 Hz.

Stay tuned for more uplifting science!

2007 Adrik McIlroy/Frogwatcher Media