# Physics of sound

## Physics of sound

Frequency
Frequency is measured in Hertz (Hz) and is the number of cycles per second. To measure this you pick a point on the waveform and then follow the wave until you reach the same point again, this is 1 cycle. An easy way to measure this is to go from one peak to the next, the highest point on the waveform is called the peak and the lowest is called the trough. If you have a waveform that is completing 440 cycles per second it’s frequency is 440Hz. The more cycles per second the higher the tone that the wave is producing.

Amplitude
Amplitude is the measure of how big a soundwave actually is, it is shown on the Y axis of the above graph. It usually goes from -1 to +1 with the middle point being 0, above it is shown as -100 to +100. It represents the speaker cone moving backwards and forwards to create the sound. As the speaker cone moves forward it pushes on the surrounding air, compressing it and as it moves back it lowers the pressure of the surrounding air. The image below shows the compression and rarefaction of air as a wave passes through it and how it relates to the waveform, as you can see the peaks show where the air is most compressed and the troughs show when the air is most decompressed. This diagram also shows that sound waves are longitudinal waves, as they travel through the air they vibrate back and forth in the opposite direction to the source i.e a speaker or a mouth.

Wavelength
Because all sound is travelling at the speed of sound the wavelength dictates the actual sound we hear. Sound waves with a long wavelength have a lower frequency of waves and therefore sound lower. Sound waves with shorter wavelength have a higher frequency of waves and therefore sound higher.

Velocity
Velocity is the speed at which the sound wave travels through the air. At sea level with a temperature of 20 degrees celsius the speed of sound is 340 meters per second when travelling through air. It is dependent on the density and temperature of...