Sound: Origin, Propagation and Measurement

Sound is a mechanical wave that travels through a medium such as air, water, or solids.
Sound is produced by the vibrations of particles, for example, when a guitar string is plucked or a speaker is powered.
The particles of the medium pass the vibration on to neighboring particles, creating a wave movement.
Our ear perceives these mechanical waves as noises, tones, or sounds.
Sound always needs a {carrier medium}{A carrier medium is something that transports information, energy, or signals from one place to another. For example, air is the carrier medium for sound because it transmits the vibrations.} and cannot propagate in a {vacuum}{A vacuum is a space where almost no particles like air or dust are present. Because there is almost nothing, sound waves cannot spread and you hear nothing.}.
Sound transmission
⚙ einfuhrung

Sound is produced when a body (for example, a tuning fork, speaker, or our vocal cords) is set into vibration.
These vibrations are transferred to the surrounding air particles as they move back and forth.
This results in a continuous sequence of compressions and rarefactions of the air, which propagates in waves.
Further Examples:
- When a drum is hit, the drum skin is set into vibration.
- When speaking or singing, our vocal cords vibrate.
- A motor generates sound vibrations through mechanical movement of its parts.
⚙ entstehung

Sound propagates in the form of longitudinal waves. This means the direction of vibration of the particles is along the direction of propagation of the wave.
Key features of sound propagation:
- Sound needs a medium (air, water, solids).
- In vacuum, sound cannot be transmitted.
- Sound travels faster in solids than in gases, because the particles are closer together.
Example: You hear an approaching train over the rails more quickly if you put your ear to the tracks than through the air.
⚙ ausbreitung

Sound can be measured by various quantities:
- Sound level: Indicates the loudness of the sound, usually in decibels (dB), measured with a sound level meter.
- Frequency: Measures the pitch of a sound, i.e., how many oscillations occur per second (in Hertz, Hz).
- Amplitude: Measures the maximum displacement of a vibration and is associated with loudness.
A typical measurement procedure:
1. Placement of a microphone near the sound source
2. Conversion of sound into an electrical signal
3. Analysis using a measuring device or computer
⚙ messen

Frequency (unit: Hertz, Hz) describes the number of oscillations of a sound wave per second.
High frequencies are perceived as high tones (e.g. flute), low ones as deep tones (e.g. bass).
The human hearing range is approximately from 20 Hz to 20,000 Hz. As we age, the upper limit often decreases.
⚙ frequenz

Amplitude refers to the maximum displacement of a vibrating quantity.
With sound waves, a higher amplitude means louder perception. In diagrams, amplitude can be seen as the distance from the center line to the wave peak.
Example: A soft whisper has a small amplitude, a loud bang a large one.
⚙ amplitude

Speed of sound indicates how fast sound travels through a certain medium.
In dry air at 20 °C, it is about 343 m/s. In water, it is about 1,480 m/s, and in solid materials like steel, up to 5,000 m/s.
It depends on the medium and its temperature. Rule of thumb: The denser the medium, the faster sound propagates.
Example from everyday life:
During a thunderstorm, you often see the lightning first and then hear the thunder. This is because light travels much faster than sound. If you count the seconds between lightning and thunder, you can calculate how far away the storm is:
- Rule: For every 3 seconds, the distance is roughly 1 kilometer, since sound travels about 343 m/s.
- Example: If you count 6 seconds between lightning and thunder, the storm is about 2 kilometers away.
By counting the seconds, you can use the speed of sound to easily estimate how far away the storm is.
⚙ schallgeschwindigkeit

The loudness of sound is measured in the unit decibel (dB).
It is a logarithmic unit, which describes the ratio between two sound intensities.
Even small changes in the decibel range are clearly perceived by the human ear.
For example: Normal conversation is about 60 dB, street traffic about 80 dB, and a jackhammer up to 120 dB.
⚙ dezibel

Sound sources are found everywhere in everyday life. The most important include:
- Musical instruments: Guitar, piano, trumpet – the strings or air columns vibrate and create characteristic tones.
- Voice: When speaking or singing, vocal cords vibrate and create speech sounds or singing.
- Household appliances: Mixer, washing machine or vacuum cleaner produce sound through mechanical movements.
- Nature: Thunder, birdsong or the splashing of water are natural sound sources.
- Technology: Sirens, engines or all kinds of machines.
This diversity makes sound an important part of our daily life.
⚙ beispiele