How to measure noise?

Some people are naturally open-minded and cannot be swayed by thunder.

Some people are very sensitive; even a gust of wind can wake them up.

Today's society

Young people are under increasing pressure

My ears are becoming more and more sensitive.

But in fact, the country has been working hard to protect our physical and mental health.

for example:

Different people have different requirements for sound.

But how can I know?

Your environment is indeed affected by noise pollution.

This is where we need to talk about tools specifically designed for measuring noise.

Sound level meter

A sound level meter is the most basic noise measuring instrument. It is an electronic instrument, but it differs from objective electronic instruments such as voltmeters. In converting sound signals into electrical signals, it can simulate the time characteristics of the human ear's response to sound waves; it exhibits different sensitivity characteristics and intensity characteristics that change at different loudness levels. A sound level meter is a subjective electronic instrument.

The function of a sound level meter

Sound level meters can be used to measure and manage noise from a wide variety of sources, including factories, road and rail traffic, and construction projects. Beyond typical urban environments such as sporting events, outdoor concerts, recreational parks, and residential and commercial districts, there are many different sound sources, each with distinct characteristics, presenting specific challenges for professionals assessing them.

What is the working principle of a sound level meter?

A sound level meter consists of a microphone, a preamplifier, a signal processor, and a display screen. The microphone converts the sound signal into an equivalent electrical signal. The most suitable microphone type for a sound level meter is the condenser microphone, which offers high accuracy, stability, and reliability. The electrical signal generated by the microphone is very weak, so it is first amplified by a preamplifier before being processed by the main processor.

Signal processing includes frequency weighting and time weighting of the signal in accordance with international standards (such as IEC 61672-1, to which sound level meters conform).

Time weighting

Time weighting refers to how a sound level meter responds to changes in sound pressure. It is the exponential average of the fluctuating signal, providing an easily readable value. The analyzer employs fast, slow, and impulsive (or "F", "S", and "I") time weightings, which are required by most international and national standards. Environmental assessment standards typically specify which time weighting to use.

The signal is processed by a weighting filter and the sound pressure level is displayed on the analyzer screen in decibels (dB), with a reference value of 20 μPa. The sound pressure level value is updated at least once per second.

In short, assessing a changing noise level means obtaining an average sound level value. Worldwide, the "equivalent continuous sound level" (Leq) is known as the fundamental averaging parameter. Leq represents the amount of energy in the measured fluctuating sound pressure level, and it remains stable during the measurement. It measures the average energy over varying sound levels.

Although numerous studies have shown a strong correlation between Leq and annoyance level, it is not a direct measure of annoyance level.

Leq can be measured directly using a high-performance sound level meter (sometimes called an integrating sound level meter). If an A-weighted filter is used, it is represented as LAeq, which is the measurement of the equivalent continuous sound level through an A-weighted filter.

Frequency weighting

Frequency weighting adjusts how a sound level meter responds to different sound frequencies. This is necessary because the human ear's sensitivity to sound varies with frequency. IEC 61672-1 defines frequency weightings A, C, and Z, but other frequency weightings are occasionally used in specialized applications.

A-weighted - dBA/dB(A)

A-weighting adjusts the signal in a way similar to the human ear's response at moderate sound levels. It is based on a 40 dB equal-loudness curve. The symbol for the noise parameter usually includes the letter "A" (e.g., LAeq), indicating that the frequency weighting has been included in the measurement.

Almost all environmental and workplace noise measurements require A-weighting, as mandated in international and national standards and guidelines. A-weighting filtering covers the entire audio range from 10 Hz to 20 kHz.

C-weighted - dBC/dB(C)

The human ear's response varies with sound level. C-weighting corresponds to the 100 dB equal-loudness curve, meaning the human ear's response at relatively high sound levels. C-weighting is primarily used to assess the peak value of high sound pressure levels. It can also be used to measure recreational noise, but the transmission of low-frequency noise may be problematic.

Z-weighted - dBZ/dB(Z)

"Zero" frequency weighting is a flat frequency response between 10 Hz and 20 kHz ± 1.5 dB, excluding the microphone response.

Today, A-weighting networks are the most widely used frequency weighting methods. C-weighting is not very relevant to subjective testing because equal loudness curves are based on experiments using pure tones-most ordinary sounds are not pure tones, but rather very complex signals composed of many different tones.

How to use a sound level meter

The accuracy of measurement results is directly affected by whether a sound level meter is used correctly. Therefore, it is necessary to introduce the use of a sound level meter.

1. Selection of sound level meter usage environment: Select a representative test location. The sound level meter should be placed away from the ground and walls to reduce the additional effects of sound reflected from the ground and walls.

2. Weather conditions require that the sound level meter's microphone diaphragm be kept clean during rainless and snowless times. A wind shield must be used when the wind force is level 3 or above (to avoid wind noise interference). Measurements should be stopped when the wind force is level 5 or above.

3. Open the sound level meter carrying case, take out the sound level meter, and put the sensor on.

4. Set the sound level meter to measurement mode, check the battery, and then calibrate the sound level meter.

5. Refer to the table (a common reference for ambient sound levels) and adjust the measurement range.

6. Now you can use various functions such as fast (measuring instantaneous values ​​in environments with large changes in sound pressure level), slow (measuring average values ​​in environments with small changes in sound pressure level), pulse (measuring pulse sound sources), and filter (measuring sound levels in a specified frequency band) to perform measurements.

7. Record data as needed, and can also connect to a printer or other computer terminal for automatic data collection. Organize equipment and return it to its designated location.

How to maintain a sound level meter

1. Keep the exterior of the instrument clean;

2. Microphones should be stored in a dry place when not in use;

3. The microphone diaphragm should be kept clean and should not be touched by hand;

4. If the instrument is not used for a long period of time, it should be powered on for 2 hours per month, and during the rainy season, it should be powered on for 2 hours per week.

5. Remove the batteries promptly after using the instrument;

6. Send the samples to the metrology department for verification regularly.