Sound Measurement Glossary
Essential terms and definitions for understanding acoustics and noise measurement
This comprehensive glossary covers key terms in acoustics, sound measurement, and hearing health. Understanding these concepts helps you make better use of our decibel meter and interpret measurements accurately.
A-Weighting (dBA)
A frequency weighting that adjusts sound measurements to match human ear sensitivity, reducing low and high frequency emphasis. Most common for environmental noise measurements.
Acoustic
Relating to sound or the science of sound. Acoustic properties determine how sound behaves in a space.
Ambient Noise
The background sound level present in an environment, excluding specific sound sources being measured.
Amplitude
The maximum displacement of a sound wave from its equilibrium position, determining the loudness of sound.
Anechoic Chamber
A room designed to completely absorb sound reflections, creating a free-field environment for acoustic testing.
Attenuation
The reduction of sound intensity as it travels through a medium or passes through a barrier.
Audiometry
The testing of hearing ability, typically measuring the quietest sounds a person can hear at different frequencies.
Background Noise
Unwanted environmental sound that interferes with the perception or measurement of desired sounds.
Bandwidth
The range of frequencies contained in a sound or that a device can process.
C-Weighting (dBC)
A frequency weighting with flatter response than A-weighting, used for measuring high-level sounds and peak values.
Calibration
The process of adjusting a sound meter to ensure accurate measurements by comparing with a known reference.
Decibel (dB)
A logarithmic unit expressing the ratio between two values of power or intensity, commonly used for sound levels.
Doppler Effect
The change in frequency of a sound wave as perceived by an observer when the source is moving relative to the observer.
Dynamic Range
The ratio between the quietest and loudest sounds a system can handle without distortion.
Echo
A reflected sound wave that arrives at the listener with sufficient delay to be heard as distinct from the original.
Equivalent Continuous Level (Leq)
The constant sound level that would produce the same energy as the varying sound levels over a measurement period.
Exchange Rate
The decibel increase that results in halving the allowable exposure time (3 dB for equal energy, 5 dB for OSHA).
Fast Response
A meter setting with 125ms time constant, suitable for measuring fluctuating sounds.
Frequency
The number of sound wave cycles per second, measured in Hertz (Hz), determining pitch.
Frequency Weighting
Filters applied to sound measurements to emphasize certain frequencies, like A, C, or Z weighting.
Hearing Conservation Program
Workplace program required when noise exposure exceeds 85 dBA, including monitoring, protection, and testing.
Hertz (Hz)
Unit of frequency equal to one cycle per second. Human hearing ranges from 20 Hz to 20,000 Hz.
Impulse Noise
Brief, sudden sounds like gunshots or hammer strikes, potentially more damaging than continuous noise.
Infrasound
Sound below 20 Hz, below the threshold of human hearing but potentially felt as vibration.
Intensity
The sound power per unit area, measured in watts per square meter, related to loudness.
Inverse Square Law
Principle stating sound intensity decreases proportionally to the square of distance from the source.
Leq (Equivalent Level)
The steady sound level containing the same energy as the actual varying sound over the same period.
Logarithmic Scale
A scale where each unit represents a multiplicative factor, used for decibels due to the ear's logarithmic response.
Masking
The phenomenon where one sound makes another sound difficult or impossible to hear.
Microphone
Transducer that converts sound pressure variations into electrical signals for measurement or recording.
NIOSH
National Institute for Occupational Safety and Health, recommending 85 dBA exposure limit with 3 dB exchange rate.
Noise
Unwanted or disturbing sound that interferes with normal activities or causes harm.
Noise Dose
Percentage of allowable daily noise exposure, with 100% representing the maximum permitted exposure.
Noise Floor
The lowest measurable sound level in a system, determined by electronic noise and environmental factors.
Noise Reduction Rating (NRR)
A number indicating the effectiveness of hearing protection devices in decibels.
Octave Band
Frequency range where the upper frequency is twice the lower frequency, used for frequency analysis.
OSHA
Occupational Safety and Health Administration, setting U.S. workplace noise standards (90 dBA PEL).
Peak Level
The maximum instantaneous sound pressure level during a measurement period.
Permanent Threshold Shift
Irreversible hearing loss caused by noise exposure damaging inner ear hair cells.
Pink Noise
Random noise with equal energy per octave, sounding more balanced than white noise to human ears.
Presbycusis
Age-related hearing loss, typically affecting high frequencies first.
Reflection
Sound waves bouncing off surfaces, contributing to reverberation and room acoustics.
Resonance
The tendency of an object to vibrate at specific frequencies with greater amplitude.
Reverberation
The persistence of sound in a space after the source stops, due to multiple reflections.
RMS (Root Mean Square)
Mathematical method for calculating average sound levels, representing effective sound pressure.
Signal-to-Noise Ratio
The level of desired signal compared to background noise, measured in decibels.
Slow Response
Meter setting with 1-second time constant, providing steadier readings for constant sounds.
Sound Level Meter
Instrument measuring sound pressure levels in decibels, with standardized frequency and time weightings.
Sound Pressure Level (SPL)
The pressure variation caused by sound waves, measured in decibels relative to 20 micropascals.
Spectrum
The distribution of sound energy across different frequencies.
Temporary Threshold Shift
Temporary hearing reduction after noise exposure, typically recovering within 16-48 hours.
Threshold of Hearing
The quietest sound detectable by human ear, defined as 0 dB at 1000 Hz.
Threshold of Pain
Sound level causing physical pain, typically around 120-130 dB.
Time-Weighted Average (TWA)
Average noise exposure over a working day, normalized to 8 hours.
Tinnitus
Ringing, buzzing, or humming in the ears without external source, often from noise damage.
Transducer
Device converting one form of energy to another, like microphones converting sound to electricity.
Ultrasound
Sound above 20,000 Hz, beyond human hearing range but used in medical and industrial applications.
Wavelength
The distance between successive peaks of a sound wave, inversely related to frequency.
White Noise
Random noise with equal intensity at all frequencies, sounding like static.
Z-Weighting
No frequency weighting (flat response), showing true physical sound levels across all frequencies.