An introduction to fundamental concepts and terms in acoustics, the science of sound.
1. What is Sound?
Sound is a vibration that is perceived by the human ear. It is produced by vibrating objects and requires a medium to propagate, as sound cannot travel in a vacuum.
Sound has three fundamental characteristics:
- Pitch: Determined by the frequency of vibration. Higher frequency results in higher pitch.
- Loudness: Related to the amplitude of vibration. Greater amplitude leads to greater loudness. Loudness is subjective, while sound intensity is the objective measure of energy passing through a unit area per unit time.
- Timbre: Also called tone quality, it indicates the unique characteristics of a sound source. It is influenced by the number, frequency, and amplitude of harmonics produced with the fundamental frequency.
2. Infrasound and Ultrasound
Infrasound: Sound waves with frequencies
below 20 Hz, inaudible to humans but perceivable by animals
such as whales and dolphins.
Ultrasound: Sound waves with frequencies
above 20,000 Hz, also inaudible to humans but detectable by
animals like bats, dogs, and cats.
3. Frequency Range
Humans can hear sounds within the frequency range of 20 Hz to 20,000 Hz, allowing us to enjoy the diverse tones of musical instruments. Human speech, however, spans a narrower range, with fundamental frequencies between 80 Hz and 1,200 Hz and harmonics extending up to 10 kHz. The typical speech frequency band is 80 Hz to 10,000 Hz.
4. Sound Pressure
Sound pressure refers to the deviation from static pressure caused by a sound wave. It is often expressed as the root mean square (RMS) value over a given period, which should be long enough to avoid affecting calculation results.
5. Additional Concepts
- Volume Velocity: The product of the particle velocity component perpendicular to a surface and the surface area.
- Damping: The reduction of energy over time or distance.
- Dynamic Range: The difference between the maximum sound pressure level an electroacoustic transducer can handle and the noise-equivalent sound pressure level.
- Transducer: A device that converts input signals in one system into corresponding output signals in another.
- Standard Microphone: A precisely calibrated microphone used for accurate sound measurements under specified conditions.
Acoustics plays a vital role in understanding sound and its properties, enabling advancements in various fields such as audio technology and communication.
