# A Comprehensive List of Acoustic Terms

Home | A Comprehensive List of Acoustic Terms

Below is a comprehensive list of acoustic terms with examples to help illustrate each term. If you have questions about anything please feel free to contact us at info@ddsacoustical.com.

## Popular Acoustic Terms and Definitions

Acoustics: The branch of physics that deals with the study of sound, its generation, propagation, and reception.
Example: Acoustics is used to understand how sound waves travel through different mediums, such as air, water, or solids, and how they interact with objects and surfaces in various environments.

Sound: A form of mechanical energy that propagates as waves through a medium, usually air, and is perceived by the human ear.
Example: When you strike a tuning fork, it vibrates, producing sound waves that travel through the air and reach your ear, allowing you to hear the pitch of the sound.

Frequency: The number of cycles or vibrations per unit of time, measured in Hertz (Hz). It determines the pitch of a sound, with higher frequencies corresponding to higher pitches.
Example: The frequency of middle C on a piano is 261.63 Hz, while the frequency of the A above middle C is 440 Hz.

Wavelength: The distance between two successive points in a sound wave that are in phase. It is inversely proportional to frequency, and both are related by the formula: speed of sound (in the medium) = frequency × wavelength.
Example: In air at room temperature, a 500 Hz sound wave has a wavelength of approximately 0.68 meters (or 68 centimeters).

Amplitude: The magnitude or strength of a sound wave, representing the intensity or loudness of the sound. Amplitude is usually measured in decibels (dB).
Example: A whisper might have an amplitude of around 30 dB, while a rock concert can reach amplitudes above 100 dB.

Decibel (dB): A unit used to express the intensity of a sound relative to a reference level. The decibel scale is logarithmic, and a 10 dB increase corresponds to a tenfold increase in sound intensity.
Example: The sound of a typical conversation might be around 60 dB, whereas a jet engine at close range can produce sounds above 140 dB.

Reflection: The bouncing back of sound waves when they encounter a boundary, such as a wall or surface, leading to echoes and reverberation.
Example: When you shout in a large empty room, you might hear your voice reflecting off the walls, creating echoes.

Diffusion: The scattering of sound waves in different directions when they encounter irregular surfaces or materials designed to disperse sound energy.
Example: Acoustic diffusers are often used in recording studios or concert halls to scatter sound and reduce standing waves and flutter echoes.

Refraction: The bending of sound waves as they pass through a medium with varying properties, such as air of different temperatures or densities.
Example: On a hot summer day, sound waves can bend upward when traveling through the warmer air near the ground, leading to an interesting acoustic phenomenon known as “temperature inversion.”

Absorption: The conversion of sound energy into heat energy when sound waves encounter porous materials like acoustic foam, fabric, or fiberglass.
Example: Acoustic panels on the walls of a home theater absorb sound reflections, reducing reverberation and improving sound quality.

Transmission: The passage of sound waves through a material, which can be either transparent or opaque to sound.
Example: Sound can easily pass through an open window, while a solid concrete wall is highly opaque to sound transmission.

Reverberation: The persistence of sound in an enclosed space due to multiple reflections and interactions with surfaces, creating a prolonged decay of sound.
Example: The reverb in a cathedral is much more pronounced and lasts longer than in a small, carpeted room.

Echo: A distinct repetition of a sound caused by a reflection arriving after a delay of more than 50 milliseconds.
Example: Standing at the edge of a canyon and shouting will produce a noticeable echo as the sound reflects off the canyon walls.

Soundproofing: The process of reducing sound transmission between spaces by using materials that block or absorb sound waves.
Example: Adding mass-loaded vinyl or double-glazed windows can help soundproof a room from external noise sources.

Acoustic Isolation: The prevention of sound transmission between two adjacent spaces to avoid interference or disturbances.
Example: In a recording studio, acoustic isolation is crucial to prevent sound leakage between adjacent recording booths.

Acoustic Treatment: The use of materials or devices to alter the behavior of sound within a space, often used to improve sound quality or reduce noise.
Example: Acoustic panels, bass traps, and diffusers are commonly used in music studios to control sound reflections and create a more balanced listening environment.

Sound Source: The object or point that generates sound waves, such as a speaker, musical instrument, or human voice.
Example: A guitar strumming, a car horn honking, or a person singing are all examples of sound sources.

Direct Sound: The sound that reaches the listener directly from the sound source without any reflections or interference.
Example: When listening to someone speaking in a quiet room, the direct sound is what you hear without any echoes.

Indirect Sound: Sound that reaches the listener after reflecting off surfaces, such as walls, ceilings, or floors.
Example: In a large hall with reflective surfaces, the indirect sound can dominate the listening experience, causing echoes and reverberation.

Standing Wave: A pattern of oscillation that occurs when sound waves reflecting between two surfaces create constructive and destructive interference, causing certain frequencies to be reinforced or canceled out.
Example: A room with parallel walls can create standing waves at specific frequencies, leading to uneven sound distribution.

Harmonics: The multiples of the fundamental frequency of a sound wave that contribute to the overall timbre or tone color of a sound.
Example: When you pluck a guitar string, it produces the fundamental frequency and its harmonics, giving the sound its unique character.

Overtones: Same as harmonics, additional frequencies present in a sound, apart from the fundamental frequency.
Example: The sound of a bell ringing includes overtones that give the bell its distinctive tone.

Timbre: The quality or tone color of a sound that distinguishes it from other sounds of the same pitch and loudness. It is determined by the presence and strength of harmonics or overtones.
Example: The timbre of a flute is different from that of a violin, even when they play the same note at the same volume.

Pitch: The perceived highness or lowness of a sound, determined by its frequency.
Example: The pitch of a whistle is higher than that of a tuba, even if both instruments are playing the same note.

Sound Waveform: A graphical representation of a sound wave over time, typically showing amplitude on the vertical axis and time on the horizontal axis.
Example: A sound waveform can show the shape of a musical note, indicating how the amplitude of the sound changes over time.

Sound Pressure Level (SPL): The measure of sound intensity or loudness, expressed in decibels (dB) relative to the threshold of hearing (0 dB SPL).
Example: A normal conversation typically ranges from 60 to 70 dB SPL, while a loud rock concert can reach levels above 100 dB SPL.

Sound Spectrum: A representation of a sound’s frequency content, often displayed as a graph showing the strength of different frequencies present in the sound.
Example: The spectrum of a piano playing a middle C note will show a peak at 261.63 Hz (the fundamental frequency) and additional peaks at integer multiples of that frequency (the harmonics).

Room Mode: Standing waves that occur within an enclosed space, causing certain frequencies to be amplified or attenuated, affecting the room’s acoustics.
Example: In a rectangular room, low-frequency room modes may cause bass frequencies to build up or cancel out at specific locations, leading to uneven bass response.

Psychoacoustics: The study of how the human ear and brain perceive and interpret sound.
Example: Psychoacoustic research helps design audio codecs that optimize sound quality while reducing file size, as seen in MP3 or AAC compression.

Binaural Hearing: The ability of humans (and some animals) to locate the direction of sound sources using two ears.
Example: Binaural hearing allows us to accurately pinpoint where a sound is coming from, aiding in spatial awareness and safety.

Sound Localization: The process of determining the direction from which a sound is coming.
Example: When playing a video game, accurate sound localization helps players identify the direction of in-game sounds like footsteps or gunshots.

Anechoic Chamber: A room designed to have minimal sound reflections and absorption, creating an environment free from echoes and reverberation.
Example: Anechoic chambers are used in audio research and product testing to measure the true performance of speakers and microphones without any interference from reflections.

Sound Reinforcement: The use of audio systems and equipment to amplify and distribute sound for live performances or public events.
Example: In a concert, sound reinforcement systems amplify the sound of musical instruments and vocals to ensure the audience can hear the performance clearly.

Resonance: The natural frequency at which an object or medium vibrates most efficiently, leading to an increase in amplitude.
Example: When a singer hits the resonant frequency of a wine glass, the glass may shatter due to excessive vibration.

Transducer: A device that converts one form of energy into another, such as a microphone (sound to electrical), or a loudspeaker (electrical to sound).
Example: A microphone converts sound waves into electrical signals, which can then be amplified and recorded.

HRTF (Head-Related Transfer Function): The filter applied by the human anatomy (head, torso, and ears) to sounds arriving from different directions, which helps in sound localization.
Example: HRTFs are used in virtual reality and 3D audio systems to create an immersive listening experience by simulating how sound interacts with a listener’s head and ears.

SPL Meter: A device used to measure sound pressure levels.
Example: Sound engineers use SPL meters to calibrate audio systems and ensure that sound levels are within safe and appropriate ranges for the audience.

White Noise: A type of noise that contains equal energy across all audible frequencies, often used for testing or masking other sounds.
Example: White noise machines are used to create a constant background sound that helps mask external noises and promote better sleep.

Pink Noise: A type of noise with equal energy per octave, resulting in a decrease in energy as frequency increases.
Example: Pink noise is an acoustic term used in audio testing to evaluate the performance of audio equipment across different frequency ranges.

Sound Envelope: The time-based description of a sound’s evolution, consisting of Attack, Decay, Sustain, and Release phases (ADSR).
Example: When playing a piano key, the ADSR envelope describes how the sound starts abruptly (Attack), gradually decreases in volume (Decay), maintains a steady volume (Sustain), and fades away after releasing the key (Release).

This expanded list of acoustic terms with examples covers various aspects of acoustics and helps to illustrate how these principles and concepts apply to real-world scenarios. Keep in mind that acoustics is a broad and interdisciplinary field, and these examples represent just a fraction of the practical applications and research in the domain of sound and its behavior. Let us know if we missed any acoustic terms.