Sound is a form of energy made by vibrations. When an object vibrates, it causes nearby air particles to move back and forth. These moving particles bump into other particles, creating a wave that travels through the air.
Examples of sound sources include:
Sound must travel through a medium such as:
Sound travels as a wave. A wave is a repeating disturbance that transfers energy from one place to another.
Sound waves are usually longitudinal waves. This means the particles of the medium move back and forth in the same direction that the wave travels.
A compression is an area where particles are pushed close together.
A rarefaction is an area where particles are spread farther apart.
Sound waves are made of repeating compressions and rarefactions.
Frequency measures how many times something vibrates each second. Frequency is measured in hertz, abbreviated Hz.
Frequency affects the pitch of a sound.
| Frequency | Pitch |
|---|---|
| Low frequency | Low pitch |
| High frequency | High pitch |
Examples:
Amplitude measures the size or strength of a sound wave. Amplitude affects how loud a sound is.
| Amplitude | Sound |
|---|---|
| Small amplitude | Quiet sound |
| Large amplitude | Loud sound |
A whisper has a small amplitude. A shout has a large amplitude.
Wavelength is the distance from one point on a wave to the same point on the next wave.
For sound waves, wavelength can be measured from:
Wavelength is usually measured in meters.
Frequency and wavelength are inversely related.
The speed of sound depends on the medium it travels through. Sound travels at different speeds in different materials.
| Medium | Approximate Speed |
|---|---|
| Air | 343 m/s |
| Water | 1,480 m/s |
| Steel | 5,960 m/s |
Sound usually travels faster through solids than liquids, and faster through liquids than gases. This happens because particles in solids are closer together, so vibrations transfer more quickly.
The speed of a wave can be calculated using this formula:
Where:
Loudness is how strong or intense a sound seems to a listener. Loudness is measured in decibels, abbreviated dB.
| Sound | Approximate Decibel Level |
|---|---|
| Whisper | 30 dB |
| Normal conversation | 60 dB |
| Busy traffic | 85 dB |
| Rock concert | 110 dB |
| Jet engine nearby | 120–140 dB |
Pitch and loudness are different.
| Concept | Depends On | Example |
|---|---|---|
| Pitch | Frequency | High note or low note |
| Loudness | Amplitude | Quiet or loud sound |
A sound can be:
Timbre describes the unique quality of a sound. Timbre is why two instruments can play the same note but still sound different.
Timbre is affected by:
An echo happens when sound reflects off a surface and returns to the listener.
Examples:
Echoes are used in technology such as sonar.
Sonar stands for Sound Navigation and Ranging. Sonar uses sound waves to detect objects underwater.
A sonar system sends out a sound wave. The wave reflects off an object and returns. By measuring how long the sound takes to return, the system can calculate the distance to the object.
Sonar is used by:
Computers can record and analyze sound by converting sound waves into digital data.
A microphone detects changes in air pressure and converts them into electrical signals. A computer then stores those signals as numbers.
Digital sound is often shown as a waveform. A waveform is a visual picture of sound.
Sampling rate means how many times per second a computer measures a sound. It is measured in samples per second or hertz.
| Sampling Rate | Common Use |
|---|---|
| 8,000 Hz | Basic voice recording |
| 44,100 Hz | CD-quality audio |
| 48,000 Hz | Video audio |
A higher sampling rate can capture more detail, especially for higher frequencies.
Bit depth describes how much detail is stored for each sound sample. Higher bit depth allows a recording to store more accurate volume levels.
Common bit depths include:
A computer can analyze sound to find patterns.
Sound analysis can be used to identify:
Examples of sound analysis technology:
Music software can identify notes, beats, rhythm, and pitch.
Voice assistants use sound analysis to understand spoken words.
Some systems can recognize voices or detect unusual sounds.
Doctors can analyze heartbeats, breathing sounds, and ultrasound images.
Engineers can study machine sounds to detect problems before machines break.
Scientists can study animal sounds, ocean sounds, and noise pollution.
| Term | Meaning |
|---|---|
| Sound | Energy caused by vibrations |
| Vibration | Back-and-forth movement |
| Medium | Material that sound travels through |
| Wave | A disturbance that transfers energy |
| Longitudinal wave | Wave where particles move in the same direction as the wave |
| Compression | Area where particles are close together |
| Rarefaction | Area where particles are spread apart |
| Frequency | Number of vibrations per second |
| Hertz | Unit for frequency |
| Amplitude | Height or strength of a wave |
| Pitch | How high or low a sound seems |
| Loudness | How strong a sound seems |
| Decibel | Unit for measuring sound level |
| Wavelength | Distance between matching points on a wave |
| Timbre | Unique sound quality |
| Echo | Reflected sound |
| Sonar | Technology that uses sound waves to detect objects |
| Sampling rate | Number of sound measurements taken per second |
| Bit depth | Amount of detail stored in each sound sample |