Effects of Humidity on Sound Propagation

Contrary to what many people think, there is more sound
attenuation in dry air than in damp air.
This effect is sigificant only at frequencies above 2kHz.
This means that high frequencies will be attenuated more
with distance than low frequencies will be, and that the
attenuation will be greatest when the relative humidity
is approximately 20 percent or less.

Basics

Alright, let's start with the basics.

Sound waves travel approximately 344m/sec (1130ft/sec) in air.
Audible sound covers the frequency range from about 20Hz to 20kHz.
The wavelength of sound of a given frequency is the distance between
successive repetitions of the waveform as the sound travels through air.
It is given by the following equation:

wavelenght = speed / frequency

or, using the abbreviations of c for speed, f for frequency, and
l for wavelength:

l = c/f

Period (T) is defined as the time required for one cycle of the waveform. T=1/f.

For f= 1kHz, T=1/1000, or 0.001 sec, and l=344/1000, or .344m (1.13ft.).


So far this is the first lesson, hope you enjoyed it and you're keeping some facts said.