Acoustic Terms and Definitions

The science of sound! In order to make environment sound more neutral and increase quality of recordings, you need to know basic acoustic terms. We're here to help!

Acoustics is a branch of physics that deals with the study of mechanical waves such as vibration, sound, ultrasound and infrasound.

Airborne Noise is a sound that is transmitted by the air, like music or speech. Sound waves are picked up and carried by air until they crash into something solid, like a wall. The collision sends vibrations through the wall and into the space beyond it.

Attenuation is a measure of the energy loss of sound propagation in media. Acoustic attenuation in a lossy medium plays an important role in many engineering fields, such as vibration and noise reduction.

Baffle or sound baffle is a construction or device which reduces the strength (level) of airborne sound. Sound baffles are a fundamental tool of noise mitigation, the practice of minimizing noise pollution or reverberation. Sound baffles are applied to walls and ceilings in building interiors to absorb sound energy and thus lessen reverberation.

Bass traps are sound energy absorbers which are designed to reduce low frequency sound energy. The purpose of that is to achieve a flatter low frequency room response by reducing low frequency sound resonances in rooms.

Cloud are horizontal free-hanging absorption panels that are suspended from a ceiling. They also reduce levels of airborne sound.

The decibel (dB) is a logarithmic unit used to measure sound level. For example, a whisper is about 30 dB and normal conversation is about 60 dB.

Echo is a reflection of sound that arrives at the listener with a delay after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room.

Flanking Sound or flanking noise consists of sound vibrations that bypass the sound attenuation components in wall or floor assemblies between rooms or suites.

Flutter Echo is a series of rapid, repeated reflections caused by soundwaves bouncing around between parallel reflective surfaces.

Footfall noise occurs with an actual physical impact on the floor above. It might be a footstep or a chair dragging on the floor.

Frequency or audio frequency (or AF) is a periodic vibration whose frequency is in the band audible to the average human, the human hearing range. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.

Impact Isolation Class Rating (IIC) is a rating of impact sound insulation. Impact sound is the sound of impact on a floor surface, like the sound of footsteps on the floor above. It only applies to sound transmitted down through a floor and ceiling. It does not apply to walls.

The International Building Code (IBC) requires that a floor-ceiling separating condominiums, apartments, hotel rooms, or other dwelling units be designed for an IIC of 50 or higher.

Impact Noise or impact sound is a form of structure-borne sound that occurs when an object impacts on another, resulting in the generation and transmission of sound.

Noise Control Products are products that reduce the sound pressure level (also referred to as “NOISE”) by absorbing sound energy. Sound absorption materials do not reflect sound waves m but rather absorb them as a sponge. Good example of sound absorption material is Acoustic blanket Producer’s choice. As sound reaches the blanket it is not reflected, but instead goes through the blanket and spends its energy on vibrating the fibers of inside the blanket. The energy is converted into small amounts of heat. Sound Absorption products have to be porous so the sound can get in, such as foam, fibers, porous stone etc.

Noise Control Products are used to cancel sound reflections and echo.  Efficiency of different materials at sound absorption is measured by using a single value number, known as NRC = Noise reduction coefficient.  NRC 1.0 means 100% sound absorption.  NRC 0.8 means 80% Sound absorption.

Noise Reduction Coefficient or NRC rating is most commonly used to rate general acoustical properties of acoustic ceiling tiles, baffles, banners, office screens, and acoustic wall panels. It is occasionally used to rate floor coverings.

An NRC of 0.0 indicates the object does not attenuate mid-frequency sounds, but rather reflects sound energy. This is more conceptual than physically achievable: even very thick concrete walls will attenuate sound and may have an NRC of 0.05. Conversely, an NRC of 1.0 indicates that the material provides an acoustic surface area (in units sabin) that is equivalent to its physical, two-dimensional surface area. This rating is common of thicker, porous sound absorptive materials such as 2"-thick fabric-wrapped fiberglass panel. Materials can achieve NRC values greater than 1.00.

The noise reduction coefficient is the arithmetic average, rounded to the nearest multiple of 0.05, of the absorption coefficients for a specific material and mounting condition determined at the octave band center frequencies of 250, 500, 1000 and 2000 Hz

Reverberation or reverb, is created when a sound or signal is reflected causing numerous reflections to build up and then decay as the sound is absorbed by the surfaces of objects in the space – which could include furniture, people, and even air.

Reverberation time or decay time is a measure of the time required for reflecting sound to "fade away" in an enclosed area after the source of the sound has stopped. Reverberation time is important in defining how a room will respond to acoustic sound.

The optimum reverberation time for a space in which music is played depends on the type of music that is to be played in the space. Rooms used for speech typically need a shorter reverberation time so that speech can be understood more clearly.

Sound Absorption or acoustic absorption refers to the process by which a material, structure, or object takes in sound energy when sound waves are encountered, as opposed to reflecting the energy. Sound absorbing materials (in our acoustic panels) are meant to improve the quality of sound within a room by controlling sound reflections.

Sound Barrier are materials help to block sound and noise or create soundproof walls, ceilings, or enclosures for noisy equipment.

Sound Blocking Products are products that stop the sound from going through it.   Sound Blocking material reflect the sound, instead of absorbing it. The sound bounces off the soundblocking barrier kind of like a tennis ball bounces off a wall.  Sound Blocking materials do not reduce sound energy, but rather work as a barrier on the way of a sound wave.  This process is known as Sound Transmission Loss. (STL) Sound blocking Products are used to stop sound from going from one room to another.  Sound Blocking material are usually solid, like brick, steel, concrete wall.

Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone. The SI unit of sound pressure is the pascal (Pa).

Soundproofing is the isolating of the room from the outside world. It also reduces sound leakage between rooms.

Sound Transmission Class or STC is an integer rating of how well a building partition attenuates airborne sound. In the US, it is widely used to rate interior partitions, ceilings, floors, doors, windows and exterior wall configurations. The higher the value, the better a structure is at reducing airborne sound. For example, STC rating of 60 indicates good soundproofing - most sounds will not disturb neighboring residents.

Standing wave is a low frequency resonance that takes place between two opposite walls as the reflected wave interferes constructively with the incident wave. The resonant frequency depends on the distance between the two walls. By cutting the frequency, you can eliminate the problem.

See also: A little about sound - Basic characteristics.