Sound Level Meter – Overview

What is Sound Level Meter?

A Sound Level Meter (SLM) is a compact portable instrument, usually battery-powered, used to measure sound-pressure levels directly while incorporating frequency weighting networks that approximate the inverse of equal loudness contours at various levels. A sound level meter is also called a sound pressure level meter (SPL). To understand what SPL is, we must first understand what “Sound Pressure” is.

What is Sound Pressure?

Sound pressure (p) is the average variation in atmospheric pressure caused by sound. The unit of pressure measurement is the pascal (Pa). Since it is not intuitive to use pascal (Pa) to refer to the volume of sound in our daily lives, it is easier to describe them in decibels. As a result, sound pressure (Pa) is typically converted into “sound pressure level” in decibels (dB) to represent the sound volume.

The conversion of “sound pressure” (Pa) to “sound pressure level” (dB) is as follows.

SPL = 20*Log10 ( P / Pref)

According to the International Standards (IEC 60942:2017), Sound Level Meter is categorized into two different classes based on its accuracy:

• Class 1—Precision grade with a tolerance of ±0.5 dB. It is ideal for industrial and laboratory use. 
• Class 2—General purpose grade with a tolerance of ±1.0 dB. It is ideal for basic noise environmental measurements.

What is a normal sound level?

The World Health Organization (WHO) defines a “normal” sound level as anything below 35 decibels (dB). This is roughly equivalent to the noise of a whisper or rustling leaves. Above this threshold, any increase in loudness can cause stress, fatigue, and even hearing loss over time. For instance, levels above 85 dB are considered hazardous Noise pollution is a growing problem in our world, with sound levels above 35 dB potentially causing physical and mental health issues. WHO recommends keeping noise lower than 85dB to avoid the risk of hearing loss or fatigue over time. for human ears and may require protective equipment such as earplugs or headphones.

In many places worldwide, especially urban areas with traffic noise, normal sound levels often exceed these recommended thresholds. It is essential to understand how excessive noise affects us so that we can take measures to reduce its harmful impacts on our environment and ourselves.

How will you measure the sound level?

Measuring the sound level is essential to evaluate the acoustic environment of a particular space. Many different techniques and instruments are used to measure sound levels, including sound level meters, sound analyzers, and noise dosimeters.

Sound level meters measure the instantaneous sound pressure level in decibels (dB) and are usually used to determine the overall sound pressure level in a given area. Noise dosimeters measure an individual’s cumulative exposure over time and are often used to measure orientation in hazardous environments.

By measuring the sound levels of a particular area, it is possible to determine if the noise levels are suitable for workers and occupants. It can also be used to evaluate any unwanted noise space, we can decide if it is within an acceptable range or not. For example, if a sound level meter is used in an office environment and the results show that the sound level is too high, the table range is defined by local laws and regulations. Additionally, sound level measurements can help to identify areas where soundproofing may be necessary or beneficial.

What are the types of sound level meters?

There are three kinds of sound level meters based on how they measure the sound,  the “conventional” sound level meter, the integrating-averaging sound level meter, and the integrating sound level meter.

• Standard sound level meter

The standard sound level meter, also known as an exponentially averaging sound level meter, uses a root-mean-square (RMS) circuit to convert an AC signal from the microphone to a DC signal. Standard sound level meters are limited to determining the risk of hearing damage.

• Integrating or integrating-averaging sound level meter

Since integrating and integrating-averaging sound level meters are functionally comparable, they are frequently grouped together. The integrating meter calculates sound exposure using pressure squared into time, in contrast to the conventional sound level meter, which adds frequency-weighted noise.

Integrating or integrating-averaging sound level meters, in contrast,  is widely applied in occupational noise control and management. 

How to Pick a Sound Level Meter?

First, one needs to determine what noise environment needs to be measured. Class 1 is more accurate but more expensive than Class 2. Some other additional features that may be considered are the octave band and octave band analysis. With the function of octave band and octave band analysis, one can export the NC curve and diagnose the noise source. Last but not least, time history recording is an essential feature if there is a need for signal analysis. 

How Does Sound Level Meter Work?

The sound level meter consists of 3 main basic parts; a microphone, electronic circuits, and a display.The microphone contains a flexible membrane that detects small air pressure variations associated with sound and converts them into electrical signals. These signals are then processed using the electronic circuitry (see pict below), detected, and then displayed the sound level in decibels on the meter screen.

Standard sound level meters are designed to read the sound level with fast or slow exponential time averaging (IEC 60804:2000):

• • Fast exponential time averaging has a 125 ms exponential time constant , that corresponds to the integration time of the ear (The human ear does not represent a linear system and does not register sounds with a duration less than 125 ms).

• • Slow exponential time averaging has a 1s exponential time constant, that estimates the average noise level with a greater precision.

Why Do You Need Sound Level Meter?