The Science of sound

The ambient noise level above which signals must be presented or noise sources measured.

To reduce airborne sound transmission.

A complete positive (forward) and negative (backward) movement of a vibration corresponding to a high and low pressure wave.

The loss of energy in a vibration system, usually through friction.

Sound waves arriving at the listening location directly from the source. Differing from reflected sound, which arrives at the listening location after bouncing off the surrounding surfaces.

A distinctly discernible reflection, or repetition of a source signal. Note: The term is often used incorrectly to refer to reverberation which consists of densely spaced, indistinguishable reflections.

The ability to do work (to move an object a distance for example)

The principle now used to achieve diffraction of acoustical waves, analogous to optical grating by which light is broken into its component colors as when passing through a prism.

An acoustical diffraction grating to produce diffusion of sound.

The way in which sound is absorbed by the audience; stepping or raking the seating reduces the absorption, and improves sight lines.

Sound dislocated from its correct position, to be more left and / or right of center.

Reflected energy that occurs a greater distance away from the source than an early reflection. Sometimes referred to as “slap-back” or echo.

The first wavefront falling on the ear determines the perceived direction of the sound.

Any unwanted sound picked up by (or “leaking” into) a microphone from another instrument or loudspeaker. Sound from one room that is heard in another.

A wave in which vibrations are in the direction of propagation of sound as are sound waves in air.

A device that changes sound waves into electric signals.

undesired sound. Or random vibrations.

(NC) Standard spectrum curves by which a given measured room’s ambient noise may be described by a single NC number.

(NIC) A single-number rating calculated in accordance with Classification E 413 using measured values of noise reduction. It provides an estimate of the sound isolation between two enclosed spaces that are acoustically connected by one or more paths.

(NRC) The arithmetic average of the Sound Absorption Coefficients of a material at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. This is the range having the most impact upon speech intelligibility.

Back and forth movement that repeats regularly between two fixed positions.

The study of the perception of sound.

Noise whose instantaneous amplitude is not specified at any instant of time

Sound Navigation And Ranging, is the process of listening to specific sounds to determine where objects are located. In active SONAR, a sound is transmitted and the listener uses its echo to locate objects. In passive SONAR, the listener uses the sounds emitted directly from the source of the sounds.

How strongly an organ or living thing reacts to something. For example, the ears are sensitive to sound while the eyes are sensitive to light.

Energy that is transmitted by pressure waves in air (as well as water or solids) and is the objective cause of the sensation of hearing. The phenomenon caused by the vibration of the eardrum. The drum itself is set into motion by pressure waves traveling through the air, originating at the sound source.

Generic term for composition material available at building supply stores to dampen impact noise in floors and provide de-coupling in walls. Installing with nails or screws reduces its effectiveness.

A pressure-sensitive device which measures loudness.

The concentration of sound to levels harmful to the natural environment (including humans)

A dynamic variation in atmospheric pressure. The pressure at a point in space minus the static pressure at that point.

(SPL) The fundamental measure of sound pressure. The measurement of what sound we hear expressed in decibels in comparison to a reference level.

Whatever object makes the sound. All of these are sources of sound: two hands clapping together, a person speaking or singing, a submarine echolocating, a radio playing, birds chirping, ocean waves crashing on the beach.

vibrations of air molecules that travel through air carrying energy with them. Sound waves can also travel through water and solids, but cannot travel in space where there are no molecules to vibrate. When sound travels through air, the molecules do not actually move to a new location, instead each set of molecules “bumps” the molecules next to it, progressively transferring motion to new sets of molecules farther and farther away from the sound source until the wave motion dies out.

The speed at which sound travels. This is very important for scientists who study sound. In air sound travels 343 meters in 1 second (767 miles per hour), but in water sound travels 1500 meters in 1 second (3350 miles per hour). Compare these speeds to cars traveling on the highway at 65 miles per hour.

(TWA) The yardstick (standard of measurement) used by the Occupational Safety and Health Administration (OSHA) to measure noise levels in the workplace. It is equal to a constant sound level lasting eight hours that would cause the same hearing damage as the variable noises that a worker is actually exposed to. (This hearing loss, of course, occurs over long-term exposures.) Same as LOSHA.

A special instrument used for producing a specific tone (frequency) when the fork is struck.

A visual meter indicating the RMS value of a signal. Since the human perception of loudness corresponds to the RMS value of the signal, VU meters indicate volume (VU stands for Volume Units). Zero VU is considered to be standard operating level.

Oscillation - a shaking back and forth movement.

The unit of acoustical (or electrical) power.

A moving disturbance that transfers energy. The Substance the wave moves through does not travel with the energy.

An electronic filter in a sound level meter, which approximates, under defined conditions, the frequency response of the human ear. The A-weighting network is most commonly used.