How can you correctly measure noise?

You may be engaged in noise measurements in a workshop, measuring with all objects running simultaneously. If you stay there, you will get the data for all objects and the overall sound pressure level in the room. In many cases, background noise may drown out the particular machine noise during measurement. How do you eliminate the background noise and correct the influence?

What you need to do is to measure the sound pressure level with the objects running, and then switch off the objects and measure the background level, calculate the difference between these amounts, locate this on the horizontal axis on the graph below, go up until you intersect the graph, and then go to the vertical axis to the left. Subtract this value from the overall level, and you get the machine sound pressure level. Alternatively, you can utilise the equation to get the result.

Background noise matters to our noise measurement. Before measurement, we have to observe the environment to measure the noise level and identify the ideal location of the monitoring station. There are numbers of points we need to pay attention to when observing the environment. How many noise sources can you find in the environment? What characteristics do the noise sources have? Which location at the site can we pinpoint most of the noise sources? At the site, which directions do the noise sources come from? How far apart are the noise sources? Are there any walls/structures that may cause reflection?

Besides background noise, external factors such as the angle of the sound level meter are placed, and the weather impacts the monitoring. Do we cover most of the noise sources? Is the station close to the noise sources? Is the area encountering human activities? Do we have a good wifi signal and a stable electricity supply? Last but not least, is it safe to access?

After identifying the monitoring location, let us find out what instrument we need for noise measurement.

By: ANewR Consulting Limited, a digital environmental consultant headquartered in Hong Kong since 2008. Our expertise has grown into the context of air and water qualities, noise, green building, waste management, and remediation. With extensive know-how in environmental planning and assessment, feasibility study and policy review, ecological design, monitoring, and audit (EM&A), ANewR has matured to be a leading management consultancy. Standing in the digital transformation reign, ANewR has participated in various environmental digital projects – interactive 3D visualisation, immersive automation virtual environment, Virtual reality, automation system, and monitoring platforms.
(Website: https://anewr.com, LinkedIn: ANewR Consulting Group, Twitter: ANewR – Everyday Newer,
YouTube: https://www.youtube.com/channel/UCnpvmxnR9hbNxytSfBdfV8Q/videos)

The concept of noise

Put yourself into the shoes of a sleepless victim who endure mosquitos emitting a whining sound at night. Certainly, mosquitos sound would not make you lose hearing, but you can say it is noise because of the headache, hearing high-pitched noises, exhaustion, dizziness, and nausea mosquitos cause you. Noise is an unwanted sound connected with the feeling of annoyance.

What is sound? Sound is the vibration transformation into a sound wave through a medium of gaseous, liquid, or solid elastic. The sound wave variation determines whether humans can hear about the sound. Human ears can detect variations at least 20 times a second, but not more frequent than 20000 times a second (20Hz-20kHz). And, this is Hertz.

What is a decibel? dB is a ratio between received and transmitted signal strength on a log scale. 1dB is the slightest variation that human ears can detect. 3dB differences are equivalent to the double of the sound level. The sound level humans receive comprises the sound reflected from the wall and the amount of sound being transmitted into adjacent rooms.

Human ears would not receive the complete sound level emitting from the objects. A certain level would be lost in transmission. Sound power level is the acoustic energy emitted from the source. Another concept is Sound pressure level, which measures what humans hear—the sound pressure level results from the sound energy ejected from the source transmitting to a received location. Sound power is the cause, and sound pressure is the effect.

What happens if we have more than one noise source in the room? Is the result the sum of the individual sound pressures? No, it is not the sum of the particular sound pressures.

What you should do is measure the sound pressure level of each object and calculate the difference. Look at the graph below, find the dB point on the horizontal axis, and find the value on the vertical axis according to the intersection. Add the value onto the most vociferous object. Another method is to calculate the total sound power with an equation.

Now, you have an idea what sound and noise are about. How do we practically and scientifically study noise in our environment?

By: ANewR Consulting Limited, a digital environmental consultant headquartered in Hong Kong since 2008. Our expertise has grown into the context of air and water qualities, noise, green building, waste management, and remediation. With extensive know-how in environmental planning and assessment, feasibility study and policy review, ecological design, monitoring, and audit (EM&A), ANewR has matured to be a leading management consultancy. Standing in the digital transformation reign, ANewR has participated in various environmental digital projects – interactive 3D visualisation, immersive automation virtual environment, Virtual reality, automation system, and monitoring platforms.
(Website: https://anewr.com, LinkedIn: ANewR Consulting Group, Twitter: ANewR – Everyday Newer,
YouTube: https://www.youtube.com/channel/UCnpvmxnR9hbNxytSfBdfV8Q/videos)