• The instruments most commonly used to measure sound are the sound level meter, the dosimeter, and the octave-band analyzer.

Instruments generally used to measure sound include:

• Sound level meter
• Dosimeter
• Octave-band analyzer

Important factors to consider when dealing with these instruments are instrument settings, calibration, and effects of the environment on instrumentation.

Sound level meter

There are various factors that may indicate noise is a problem in the workplace. While people react differently to noise, subjective responses should not be ignored because they may provide warnings that noise may be at unacceptable levels. A sound level meter (SLM) is the basic instrument for investigating noise levels.

Sound level meters can be used to:

• Spot-check noise dosimeter performance.
• Determine an employee’s noise dose whenever use of a noise dosimeter is unavailable or inappropriate.
• Identify and evaluate individual noise sources for abatement purposes.
• Aid in determining the feasibility of engineering controls for individual noise sources.
• Evaluate hearing protectors.

Factors to consider with the use of a SLM include:

• When evaluating employee exposures, the microphone should be placed in the hearing zone of the employee being monitored.
• Sound level readings in a non-reverberant environment should be taken in accordance with the manufacturer’s instructions.
• Special considerations may be involved with the use and care of a sound level meter.

Dosimeter

Like a sound level meter, a noise dosimeter can also measure sound levels. However, the dosimeter is actually worn by the employee in order to determine the personal noise dose during the work shift or sampling period. Dosimeters can be used to:

• Take compliance measurements according to the Occupational Safety and Health Administration (OSHA)’s noise standard.
• Measure the employee’s exposure to noise and automatically compute the necessary noise dose calculations.

Factors to consider with the use of a dosimeter include:

• The microphone must be placed in the employee’s hearing zone. OSHA defines the hearing zone as a sphere with a two-foot diameter surrounding the head.
• Specific instrument settings must be selected for the dosimeter.
• Special considerations may be involved with the use and care of a dosimeter.

Octave-band analyzers

Octave-band analyzers are sound level meters that can be used to:

• Help determine the adequacy of various types of frequency-dependent noise controls.
• Select hearing protectors because they can measure the amount of attenuation (how much a sound is weakened) offered by the protectors in the octave bands responsible for most of the sound energy in a given situation.
• Divide noise into its frequency components.
  • Some sound level meters may have an octave or one-third octave band filter attached or integrated into the instrument. Usually a Type 1 (precision) sound level meter is used for octave and one-third octave analysis.
  • The filters are used to analyze the frequency content of noise. They are also valuable for the calibration of audiometers and to determine the adequacy of various types of noise control.

Frequency components may include:

• Most octave-band filter sets provide filters with the following center frequencies: 31.5, 63, 125, 250, 500, 1,000, 2,000, 4,000, 8,000, and 16,000 hertz.
• For a more detailed analysis, the spectrum is sometimes measured in one-third octave bands.
• The special signature of any given noise can be obtained by taking sound level meter readings at each of the center frequency bands. The results may indicate octave bands that contain the majority of the total sound power being radiated.