26 Definitions You Need To Know When Purchasing a Sound Level Meter

Sound level meters measure…sound. While that’s simple enough, these devices are associated with a lot of scientific jargon, which can make comparing them a difficult process. Instrument Choice Scientists have “come to the rescue” with a guide that clearly explains sound level measurement terminology, so you can make an informed comparison of products and select the best sound level meter for your needs.

Types of Sound Level Meters and Specifications

1. IEC – The International Electro-technical Commission. This organisation set many world standards for sound level technology, particularly in the area of acoustics.
2. IEC 61672 - The International standard for Sound Level Meters. The standard details performance characteristics for sound meters, together with information about testing instruments used to ensure sound meters meet manufacturers’ claims and specifies the content and structure of verification tests.
3. Class 1 – Refers to precision sound meters for laboratory and field use, as defined in IEC 61672. These meters are also known as “Type 1 sound meters”. The IEC 61672 standard favours the term “Class” rather than “Type.”
4. Class 2 – Refers to general grade meters as defined in IEC 61672. These meters were previously referred to as “Type 2.” The IEC 61672 standard favours the term “Class” rather than “Type.”
5. Type 1 – Refers to precision laboratory and field appropriate sound meters as defined in older standards. These have been superseded by the IEC 61672, which now uses “Class 1”, instead of “Type 1”.
6. Type 2 – Refers to general grade sound meters as defined in older standards. These have been superseded by the IEC 61672, which now uses “Class 2”, instead of “Type 2”.
7. Decibel (dB) – is a unit used to measure the intensity of sound. A decibel is a ratio of one value of a power (or field quantity) to another, on a logarithmic scale. A decibel is one-tenth of bel and mathematically both decibel and bel are not strictly units. They are simply a ratio between two quantities and, as such, have no dimension.
8. Frequency – Frequency is the number of whole cycles of vibration per second, and is expressed in hertz (Hz), kilohertz (kHz) or megahertz (MHz).
9. Frequency Weighting – Weighting is the adjustment of response in the frequency or time domains of a sound level meter to achieve the desired measurement.Frequency Weighting is the difference between the level of the signal indicated on the display device and the corresponding level of a constant-amplitude steady-state sinusoidal input signal, specified as a function of frequency.
10. ‘A’ Weighting – A standard weighting of the audible frequencies designed to reflect the response of the human ear to noise. Measurements made with this frequency weighting are displayed dB(A) or dBA.
11. ‘C’ Weighting – A standard that gives greater emphasis to low-frequency sounds compared to the ‘A’ weighted average. Measurements made with this frequency weighting are displayed dB(C) or dBC.
12. ‘Z’ Weighting - Z-weighting is a flat frequency response of 10Hz to 20kHz ±1.5dB. Measurements made with this frequency weighting are displayed dB(Z) or dBZ.

    

    Table 1: Displays the relationship between frequency and sound level with the A, C, and Z weighting.
13. Time Weightings (Fast, Slow, and Impulse) - The Time Weightings of Fast, Slow, and Impulse determine the speed that the sound level meter responds to changing noise levels. For example, an instrument set to slow will respond slowly to noise changes; a device configured to fast will adjust quickly to changes in noise level. Setting a device to impulse makes it respond rapidly to an increase in sound but will take longer to fall when the noise level decreases.
14. Equivalent Continuous Sound Level (Leq) – The Equivalent Continuous Sound Level (Leq) is representative of the total sound exposure over some time or an energy average noise level or a defined period.
15. LE (SEL) – This is a Leq normalised to 1 second. The application of this metric is to compare the energy of different noise events where they have different durations. LE is the sound exposure expressed as a log; Leq is LE divided by time.
16. Lp – Sound Pressure Level.
17. Ln – The Ln value is part of a statistical analysis of noise levels. The ‘n’ denotes the percentage exceedance. For example, a result of L90 means noise level remained above a certain level for 90% of the measurement time.
18. Peak Sound Pressure / Leak sound level (Lpeak)– The peak level is the actual peak of the pressure (sound) wave that is measured, not to be confused with the maximum sound level, which is the maximum noise level during measurement.
19. Octave Band Filters – A frequency range is divided up into sections or frequency bands when detailed information about a complex sound is needed. A sound level meter may provide 1:1 (or single) octave band filters or 1:3 (or third) octave band filters. An Octave is a frequency band where the highest frequency is twice the lowest frequency. E.g., an octave filter with a centre frequency of 1kHz has a lower frequency of 707Hz and an upper frequency of 1.414kHz.
20. Dynamic Range – The dynamic range is the measurable region on a sound level meter between low noise levels and overload at high sound volume levels.
21. Dose - The permitted amount Sound Exposure, multiplied by time to which a person is exposed. Dose limits are generally set up by government organisations to limit the exposure of workers to noise.
22. Dose Percentage – This is noise exposure expressed as a percentage of a fixed level for eight hours.
23. Exposure – Measured noise over time expressed in Pa2h (Pascal Squared Hours).
24. Time Weighted Average (TWA) - Using a 5 dB exchange rate, the total amount of workplace noise exposure expressed as an equivalent standard 8 hour working day.
25. Maximum Sound Level (Lmax) – Is the maximum noise level during a measurement period or noise event.
26. Minimum Sound Level (Lmin)– Is the minimum noise level during a measurement period or noise event.

Conclusion

Although sound level meters are popular and easy to use devices, some of the terminologies behind the measurements of these devices can be tricky. Understanding and referencing the 26 terms listed above will help you knowledgeably select the best sound level meter for your needs and assist you in comprehending the measurements of your product.

If you need further assistance with any of the above terms, or need a hand finding the perfect sound meter to suit your needs, contact an Instrument Choice scientist. We’re here to help!

Call 1300 737 871 or email [email protected].