There are many different types of Sound Level Meters (SLMs). Each type of SLMs serve a particular need and designed for specific application. To understand and know how to choose the right SLM for your need, you will have to understand the technical specifications of the sound level meter. In this article, we list down and explain a non-exhaustive but critical set of specifications that will help you in making the right selection when purchasing a sound level meter.

Decoding Technical Specifications of Sound Level Meters (SLMs)

Group Category Purpose Variations Representation
Classifications Specifications Standard that define and classify sound level meters. IEC 61672-1:2013 International Electrotechnical Commission (IEC) specification that define sound level meters
IEC 61672-1:2002 International Electrotechnical Commission (IEC) specification for personal sound exposure meters
IEC 61252 : 1993 International Electrotechnical Commission (IEC) specification for sound calibrators
Types IEC 61672-1 specify three kinds of sound level meters. Time-weighting SLMs Sound level meters that measure exponential-time-weighted, frequency-weighted sound levels.
Integrating-averaging SLMs Sound level meters that measure time-averaged, frequency-weighted sound levels
Integrating SLMs Sound level meters that measure frequency-weighted sound exposure levels. Sound level meters specified in this standard are intended to measure sounds generally in the range of human hearing. Two performance categories, class 1 and class 2, are specified in this standard.
Classes IEC 61672-1 defines two performance categories, class 1 and class 2 for integrating sound level meters. Both classes have the same functionality, but different tolerances for error. 1 Very precise sound level meters meant for laboratory use or for field measurements where accuracy are required. Class 1 instruments have a wider frequency range and a tighter tolerance than a lower cost Class 2 instrument.
2 General purpose sound level meters fall in this class. They are intended for general field use and for recording noise level data for later frequency analysis. They cost less than a Class 1 instrument.
Microphone Types Also known as transducer, it is the interface between the acoustic field and measuring instrument. The quality of a microphone is critical in defining the performance of a sound level meter. It determines the quality of the measured sound level data and thereby determines the accuracy of the measurements. Piezoelectric Membrane is attached to a piezoelectric crystal which generates an electric current when submitted to mechanical tension. The vibrations in the air, resulting from the sound waves, are picked up by the microphone membrane and the resulting pressure on the piezoelectric crystal transforms the vibration into an electric signal. These microphones are stable, mechanically robust and not appreciably influenced by ambient climatic conditions. They are often used in sound survey meters
Condenser Microphone membrane is built parallel to a fixed plate and forms with it a condenser. A potential differential is applied between the two plates using a d.c. voltage supply (the polarisation voltage). The movements, which the sound waves provoke in the membrane, give origin to variations in the electrical capacitance and therefore in a small electric current. These microphones are more accurate than the other types and are mostly used in precision sound level meters. However, they are more prone to being affected by dirt and moisture.
Electret A variation of the condenser microphone. In this case the potential difference is provided by a permanent electrostatic charge on the condenser plates and no external polarising voltage. This type of microphone is less sensitive to dirt and moisture than the condenser microphone with a polarisation voltage.
Dynamic The membrane is connected to a coil, centred in a magnetic field, and whose movements, triggered by the mechanical fluctuations of the membrane, give origin to a potential differential in the poles of the coil. The dynamic microphone is more mechanically resistant but its poor frequency response severely limits its use in the field of acoustics.
Measurement Frequency Weightings Frequency weightings are electronic filters within the sound level meters (SLMs) that can be adjusted in how the SLMs measures noise. Through frequency weightings,SLMs can measure and record noise levels that represent what our ears hear (our ears are most sensitive to frequencies between ~500Hz and 6kHz). A A-weighting filter covers the full audio range from 20Hz to 20kHz and correlates to the response of the ear at the lower levels.They are designed to measure noise source as an approximation to how the human ear perceives the noise.
B It was initially developed to cover the range between A and C-Weghting frequencies. It is no longer in common use due to it’s general decline in popularity.
C A common weighting used for higher level measurements and Peak sound pressure levels. The filter correlates better with the human response to high noise levels.
D The frequency weighting developed for measuring high level aircraft noise. However, it is no longer in common use since IEC 61672 2003. Recent ISO standards recommend A-weighting for commerical aircraft noise measurement.
Z It represent zero frequency weighting. The range is 10Hz to 20kHz +- 1.5dB. It was introduced in IEC 61672 2003 to replace Flat/Linear Filters
Frequency Response The deviation between the measured value and the true value as a function of the frequency. A good sound level meter should have a frequency response of less than 1 dB over the range of sound the human ear is capable of hearing (i.e. 20Hz to 20 kHz).
Dynamic Range The difference between the maximum and minimum measurable sound levels of a sound level meter. Most microphones (of SLMs) have a dynamic range of 100dB to 120dB.
Parameters List of basic measurement parameters provided by most Sound Level Meters LAeq A-weighted equivalent sound pressure level in dB measured over a period of time. It is the equivalent continuous sound pressure level. Measurements that correspond to the loudness human ear hear
LCeq C-weighted equivalent sound pressure level in dB measured over a period of time.
LCpeak C-Weighted peak sound pressure level. The LCpeak is used for occupational noise measurement (not really for environmental noise measurement) where loud bangs are present. Unlike Lmax, this is the true peak value of the sound pressure wave as there are no time constant applied and the measured signal has not passed through an RMS circuit.
Lmax Highest sound level measured by the sound level meter over a given period of time.
Lmin Lowest sound level measured by the sound level meter over a given period of time
LAE Correspond to sound exposure level. It represent the sound level of transient noise.
Time weightings The response time for each measurement of the sound level. These are time weightings that date back to the time of analogue sound level meters where it corresponds to the speed at which the meter needle moves. In digital sound level meters, these time time constant are now being calculated/simulated before displayed. Fast Corresponds to approximate 125 ms time constant. This represent that a measurement is taken at every 125 ms.
Slow Corresponds to approximate 1s time constant. This represent that a measurement is taken at every 1s.
Impulse Corresponds to approximate 35 ms time constant. This represent that a measurement is taken at every 35 ms.
Datalogging Records and store measured sound data either in sound level meter’s built -in memory or external storage card.

At Dropnoise, we carry a range of Scarlet sound level meters for you to choose from. You may also contact us if you need any advice in the selection of the right SLM for your application.

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