How big the push is
What Makes a Sound Loud?
Loudness is not about speed of vibration. It is about how far the air gets shoved.
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Step 1 of 5
Loudness and pitch are different things.
Two separate dials, often confused for one Pitch is how often the air is pushed. Loudness is how hard. You can play the same note quietly or deafeningly.
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Step 2 of 5
A bigger vibration shoves more air.
Hit a drum harder and the skin swings further. It crams the air more tightly on each push, so a stronger pressure wave leaves.
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Step 3 of 5
Your eardrum moves further.
Loudness reaches you as distance travelled by a piece of skin. A big pressure swing pushes your eardrum further in and out. More movement means a stronger nerve signal and a louder experience.
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Step 4 of 5
Loudness fades fast with distance.
Sound spreads over an expanding sphere. Double your distance and the energy spreads over four times the area, so it drops to a quarter.
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Step 5 of 5
Decibels are a squashed scale.
Each rung of 10 dB is ten times the energy, not a little more Our ears handle a colossal range, so we count in decibels. Every 10 dB is ten times the energy — 90 dB is not slightly worse than 80, it is ten times worse.
Sustained sound over about 85 dB damages hearing permanently — and the damaged cells never grow back.
The short version
Loudness is how hard the air gets pushed; pitch is how often. They are independent.
Try it yourself
Pluck a guitar string gently and then hard. Same note both times — only the size of the wobble changed.