Sound Level Meter Basics

A sound level meter is, simply a device for assessing sound level at a given instant in time and a given location. The information learned by the careful, competent use of a sound level meter is a measurement of sound pressure level, appropriately frequency weighted, at the time and location of the measurements.

For a discussion of basic acoustical physics, the attributes of sound, and the principals of operations of the sound level meter, the reader is referred to the author’s monograph “Basic Acoustics for OHV Noise Control” (Harrison 2004), Johnson et al. (1998), and Yeager and Marsh (1998). (Also see US Dept. of Labor, Occupational Safety & Health Administration site for more details on "Physics of Sound".)

What will be presented here is some general information about sound level meters for the wildlife noise impact assessment, along with some practical tips for their selection and use.

There are several standards which cover the accuracy, frequency response, operating characteristics, etc. for sound level meters. The two most important are those promulgated by the American National Standards Institute (ANSI) – "Specification for Sound Meters" (S1.4) (ANSI 1983), and the set published by the International Electrotechnical Commission (IEC) (IEC 2002). For all practical purposes, these standards are identical.

In each standard, two (or more) levels of performance are specified. More and less accurate meters for specialized purposes are also described in the standards, but the following discussion is of the Type 1 and Type 2 sound meters.

A typical sound level meter.

A Type 1 meter, referred to a "Precision" Sound level meter, is the more precise and correspondingly more expensive sound meter. This meter is intended for accurate sound measurements in the field and laboratory (ANSI 1988:1). For work which demands by its nature high accuracy, such a research into human hearing, or work for which a great deal of money depends on the detection of small differences, for instance, the assessment of aircraft noise around airports, a Type 1 meter is generally preferred.

The accuracy of a Type 1 meter could be thought of as being +/- 1.0 dB in the important frequency ranges. Whenever litigation is (or may be) involved, the use of a Type 1 meter is suggested.

A Type 2 meter, often referred to as a General Purpose sound level meter, is intended for general field use, i.e., measurement of typical environmental sounds when high frequencies do not dominate (ANSI 1988:1).

The type 2 meter is usually specified for hearing conservation assessment, measurement of vehicle noise, and, as the name suggests, for general measuring of sound levels in the industrial, residential, recreational and outdoor environments. Type 2 meters are generally thought of as being accurate within +/- 1.5 dB at the frequencies important for human hearing (ANSI 1983:1).

Note: The Type 2 meter is the minimum requirement by OSHA (Occupational Safety & Health Administration) for measurement of noise impact to humans. OSHA considers the Type 2 meter "sufficient for general purpose noise surveys". See OSHA Technical Manual (TED 01-00-015), Section III, Chapter 5, Section III; Appendix III.A "Instruments Used to Conduct a Noise Survey - Sound Level Meter ".

For almost all practical measurements, a properly calibrated and maintained Type 2 meter is more than adequate for monitoring of sound levels in the field.