Sound Level Meters
A necessary first step in developing an effective soundproofing solution involves the measurement and characterization of the noise frequently accomplished at least in part with sound level meters. The end result of this task is generally one or more plots showing the noise amplitude as a function of frequency. This information is used to determine the type and combinations of soundproofing materials needed (e.g., sound barriers or sound absorbtion), their physical characteristics (e.g., thickness, weight, size, etc.) and their configuration and placement.
A sound level meter (SLM) is the basic tool used to measure noise. Sound level meters are classified according to their accuracy, performance and calibration. Type 0 SLMs are used for laboratory calibration. Type 1 SLMs are precision grade instruments with an accuracy of ±1 dB, used for research and law enforcement. Type 2 SLMs are general use instruments with an accuracy of ±2 dB, used for industrial noise assessment. For most consumers and non-experts, a Type 2 SLM is sufficient, and expert and professional acoustic engineers will use a Type 1 SLM.
Sound level meters range from relatively low-cost (or free) smartphone apps that you can download from the internet, to SLMs that cost hundreds of dollars that can provide a single read-out of overall noise levels, to sophisticated octave-band SLM instruments that cost in the thousands of dollars that can output frequency spectra with a high degree of accuracy. Depending on your specific application, some sound level meters are better suited than others. Following is a brief review of these SLMs.
- Smartphone Sound Level Meters – Numerous apps are available for smartphones that can provide output similar to very sophisticated SLMs that cost thousands of dollars. While most professionals disregard such SLMs due to their lack of accuracy, casual users may find these useful to make rapid and educated assessments on noise levels. The smartphone SLMs use the microphones embedded in the phones, which have been optimized to enhance the quality of human voice. They therefore have a limited frequency range (from 200 to 3000 Hz) and are not suitable to measure high volume noise (over 85 dB). These smartphone SLMs can be greatly improved by the addition of an audio (music-quality) external microphone.
- Single Read-Out Sound Level Meters – These instruments will typically provide a single read-out of overall sound pressure levels in un-weighted, A-weighted or C-weighted decibels. Typically, these instruments are suitable to determine if overall sound levels over the audible frequency range exceed a certain value. For example, one OSHA standard for maximum permissible noise levels is 85 dBA over an 8 hour period, and such an instrument can be used to monitor overall noise in the environment. Another use may involve measurement of outdoor sound pressure levels to ensure that noise from an establishment of piece of equipment do not exceed overall community noise standards.
- Octave Band Sound Level Meters – These instruments can provide measurements of overall sound pressure levels as well as the frequency spectrum of the noise. The frequency spectrum can be in terms of narrowband measurements (one Hz bandwidth power spectral densities), one-third octave bands, and full octave bands. These measurements can be output in spreadsheet format for further processing and analysis. In order to develop an effective soundproofing solution, it is important to measure and understand the amplitude of noise as a function of frequency, as these acoustic characteristics will be used to select and size the soundproofing materials and develop a design.
Sonic-Shield noise and vibration engineers are experts in the use of various types and brands of sound level meters and the acquisition and analysis of noise and vibration data. We are available to assist you in the selection of sound level meters and/or in the measurement and analysis of sound level meter data for your soundproofing needs.