Sound level meter

A sound level meter (also called sound pressure level meter (SPL)) is used for acoustic measurements. It is commonly a hand-held instrument with a microphone. The best type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability.^[1] The diaphragm of the microphone responds to changes in air pressure caused by sound waves. That is why the instrument is sometimes referred to as a sound pressure level meter (SPL). This movement of the diaphragm, i.e. the sound pressure (unit pascal, Pa), is converted into an electrical signal (unit volt, V). While describing sound in terms of sound pressure, a logarithmic conversion is usually applied and the sound pressure level is stated instead, in decibels (dB), with 0 dB SPL equal to 20 micropascals.

A microphone is distinguishable by the voltage value produced when a known, constant root mean square sound pressure is applied. This is known as microphone sensitivity. The instrument needs to know the sensitivity of the particular microphone being used. Using this information, the instrument is able to accurately convert the electrical signal back to sound pressure, and display the resulting sound pressure level (unit decibel, dB).

Sound level meters are commonly used in noise pollution studies for the quantification of different kinds of noise, especially for industrial, environmental, mining and aircraft noise.^[2][3] The current international standard that specifies sound level meter functionality and performances is the IEC 61672-1:2013. However, the reading from a sound level meter does not correlate well to human-perceived loudness, which is better measured by a loudness meter. Specific loudness is a compressive nonlinearity and varies at certain levels and at certain frequencies. These metrics can also be calculated in a number of different ways.^{[4][example needed]}

The world's first hand-held and transistorized sound level meter, was released in 1960 and developed by the Danish company Brüel & Kjær.^[5] In 1969, a group of University researchers from California founded Pulsar Instruments Inc. which became the first company to display sound exposure times on the scale of a sound level meter, as well as the sound level. This was to comply with the 1969 Walsh-Healey Act, which demanded that the noise in US workplaces should be controlled.^[6] In 1980, Britain's Cirrus Research introduced the world's first handheld sound level meter to provide integrated L_eq and sound exposure level (SEL) measurements.^[7]