Sound level meter

A microphone is distinguishable by the voltage value produced when a known, constant root mean square sound pressure is applied.

[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.

Traditionally, noise dosemeters were relatively large devices with a microphone mounted near the ear and having a cable going to the instrument body, itself usually belt worn.

In 1997 following a UK research grant an EU patent was issued for the first of a range of devices that were so small that they resembled a radiation badge and no cable was needed as the whole unit could be fitted near the ear.

[7] Today these devices measure not only simple noise dose, but some even have four separate dosemeters, each with many of the functions of a full-sized sound level meter, including in the latest models full octave band analysis.

Similarly, the American National Standards Institute (ANSI) specifies sound level meters as three different Types 0, 1 and 2.

For unusual measurement situations, refer to the manufacturer's instructions and appropriate ANSI standards for guidance in interpreting instrument accuracy."

"Pattern approved" sound level meters typically offer noise measurements with A, C and Z frequency weighting.

A-weighting, weights lower and higher frequencies much less, and has a slight boost in the mid-range, representing the sensitivity of normal human hearing at low (quiet) levels.

The IEC 61672-1:2013 mandates the inclusion of an A-weighting filter in all sound level meters, and also describes C and Z (zero) frequency weightings.

However, the following can be used as a guideline: The slow characteristic is mainly used in situations where the reading with the fast response fluctuates too much (more than about 4 dB) to give a reasonably well-defined value.

Today almost all fixed airport noise monitoring systems, which are in concept just complex sound level meters, use short Leq as their metric, as a steady stream of the digital one second Leq values can be transmitted via telephone lines or the Internet to a central display and processing unit.

Short Leq is a feature of most commercial integrating sound level meters—although some manufacturers give it many different names.

Short Leq is a very valuable method for acoustic data storage; initially, a concept of the French Government's Laboratoire National d'Essais (ref 1), it has now become the most common method of storing and displaying a true time history of the noise in professional commercial sound level meters.

If the words max or min appear in the label, this simply represents the maximum or minimum value measured over a certain period of time.

Until 2003 there were separate standards for exponential and linear integrating sound level meters, but since then IEC 61672 has described both types.

New in the standard IEC 61672 is a minimum 60 dB linear span requirement and Z-frequency-weighting, with a general tightening of limit tolerances, as well as the inclusion of maximum allowable measurement uncertainties for each described periodic test.

While applying double hearing protection helps prevent auditory damage, it may compromise effectiveness by isolating the user from his or her environment.

A manufacturer has to supply instruments to a national laboratory which tests one of them and if it meets its claims issue a formal Pattern Approval certificate.

Even the most accurate approved sound level meter must be regularly checked for sensitivity—what most people loosely call 'calibration'.

For a simple single level and frequency check, units consisting of a computer controlled generator with additional sensors to correct for humidity, temperature, battery voltage and static pressure can be used.

The output of the generator is fed to a transducer in a half-inch cavity into which the sound level meter microphone is inserted.

These tests excite the sound level meter across the entire frequency and dynamic range ensuring compliance with expected design goals defined in IEC61672.1-2013.

Required for measuring the acoustics in buildings is a signal generator that provides pink or white noise through an amplifier and omnidirectional speakers.

This can be achieved using a spherical distribution aligning 12 speakers in a so-called dodecahedral configuration, as illustrated by Brüel & Kjær OmniPower Sound Source Type 4292.

Modern monitoring stations can also offer remote communication capabilities using cellular modems, WiFi networks or direct LAN wires.

[32][33] The ubiquity of smartphones, their constant network connectivity, the built-in geographic information system functionality and user-interactivity features present a great opportunity to revolutionize the way we look at noise, its measurement, and its effects on hearing and overall health.

The ability to acquire and display real-time noise exposure data raises people's awareness about their work (and off-work) environment and allows them to make informed decisions about hearing hazards and overall well-being.

The National Institute for Occupational Safety and Health (NIOSH) conducted a pilot study to select and characterize the functionality and accuracy of smartphone sound measurement applications (apps) as an initial step in a broader effort to determine whether these apps can be relied on to conduct participatory noise monitoring studies in the workplace.

Researchers concluded that smartphone sound apps can serve to empower workers and help them make educated decisions about their workplace environments.