What is Sound?

Sound is audible vibrations that travel through various mediums such as air or steel.

The first important thing to understand is air can be compressed and expanded, so its pretty much elastic.

When a speaker plays music it causes the air to compress and expand as waves, and this causes our eardrums to move in and out.










Lets consider this in slow motion… When a speaker cone pushes out it squishes nearby air molecules together, when the speaker cone pulls back in it causes nearby air to become less dense (rarefaction); these compressions and rarefactions travel away from the speaker as pressure waves. When the pressure waves reach a dynamic microphone, its diaphragm (the microphones eardrum) vibrates in the exact same pattern as the speaker cone. The diaphragm is connected to a coil of wire that vibrates back and forth past a magnet, and whenever wire moves past a magnet you get an electrical current. This tiny electrical current travels out the microphone, through the XLR cable and to the
microphone pre-amplifier where the signal is amplified to a useable level. Then the current travels to the power amplifier where the signal is amplified further and sent to our speaker. The first part of our speaker is the driver which has a cone connected to wire that vibrates back and forth past a large magnet (just like our dynamic microphone but in reverse). This causes our driver to move back and forward in the same pattern as the original microphone diaphragm, and this results in new pressure waves to travel through the air.

Sound pressure waves travel through air as a longitudinal waves. Longitudinal waves vibrate parallel to the direction they are travelling.

Transverse waves vibrate perpendicular to the medium they occur on, such as a guitar string or drum skin. The positive and negative nature of voltage is displayed as transverse waves, and the waveforms we see in in Digital Audio Workstations (DAWs) such as ProTools are transverse waves.

Next: Speed of Sound

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