Bosworth Instrument Training Sheets
Sound Level Meters, Dosimeters, Calibrators
Alternate Terms for Sound Level Meters
Sound Pressure Meters
Noise Meters
How do Sound Level Meters and Dosimeters differ?
Sound Level Meters are devices that monitor noise levels through a transducer (microphone) and display the levels in decibels (dB) on an LCD, LED, or analog display. Sound Level Meters find use in assisting in local law enforcement, recording studios, audible alarm manufacturers, and anywhere an instantaneous or averaged sound level must be monitored.
Dosimeters, on the other hand, are a full sound/noise analysis system which can be worn on a belt for personal field measurements. Accumulated noise exposure, % noise dose, exposure time, Criterion level, Exchange Rate, and Threshold enable the user to better comply with regulatory standards such as OSHA and UL. Applications which benefit from Dosimeters are those that call for the measurement of long-term noise levels under slowly varying environmental conditions such as manufacturing/workplace noise analysis, transportation organizations' regulatory compliance, and product or service noise reduction studies. For this application see the 407355 Personal Noise Dosimeter.
Why monitor noise?
There are sounds and noises throughout our environment that can cause hearing damage and physical harm if exposure is extreme. Because of this, regulations are in place and must be met by airlines, factories, and others. OSHA regulates the workplace and stresses the need for precise sound monitoring equipment in complying to their hearing-safety specifications. In addition, there are local codes that limit the level of noise that can be tolerated in local communities. Because of this, law enforcement also use sound level instruments to enforce local laws.
What is Frequency and Time Weighting?
Frequency "weighting" refers to the ability of the meter to display a uniform reading in dB for the varying frequencies of sound being measured. "A" weighting is most common and simulates the response of the human ear. "A" weighting is useful for environmental sound measurement. "C" weighting gives a more flat response suitable for machinery measurements.
Time "weighting" refers to the response of the meter. "Slow" weighting is most often used for hearing conservation or OSHA programs and is an "averaging" of sound over time. "Fast" weighting is most commonly used for product noise reduction efforts and can detect fast noise spikes.
Built-in Calibration vs. external Calibration
The 407764 has a power-on built-in self-test, the 407735 has a built-in 94dB calibration. The 407740 offers an optional external calibrator (407744) which provides a true 1kHz (94dB) signal for use with the sound level meter's microphone. External calibration assures that the microphone, as well as the electrical circuits, are calibrated. Using an external calibrator is recommended for greater accuracy. 
