Decoding Noise Pollution: Understanding, Measuring, and Mitigating Unwanted Sounds

NOISE POLLUTION

Noise Pollution Any unwanted sound produces undesirable physiological effects on the individual.

Level of Noise

Minimum sound pressure can be heard by human being=20µPa

The maximum sound produced by Rocket=200 Pa

Level denoted as $L=\log_{10}{(\frac{Q}{Q_{0}})}beles$

L=\log_{10}{(\frac{Q}{Q_{0}})}𝑑𝑒𝑐𝑖𝑏𝑒𝑙𝑠 (𝑑𝐵)

Where Q is the measured quantity and Qo is Std. reference quantity generally taken as 20µPa (if qty is taken as pressure)

Other forms of Level are

L_p=10\log_{10}{(\frac{prms}{20µPa})}^2

L_p=20\log_{10}{(\frac{prms}{20µPa})}

If the reference is power watt then

L_w=10\log_{10}{(\frac{1}{10^{-12}})}

If the reference is sound Intensity $(W/m^2)$

L_w=10\log_{10}{(\frac{1}{10^{-12}})}

Averaging the sound pressure level

\overline{L}<em>p=20\log</em>{10}\frac{1}{N}\displaystyle\sum\limits_{n=0}^N 10^{\frac{L_n}{20}}

Where $\overline{L}<em>p</em>$ is the average sound pressure level in dB having reference pressure in 20µPa, N is several measurement readings. Ln is the nth sound
pressure level in dB.

Concepts of Noise- Two kinds of Noise concepts are used to find the combined effect of different sound pressure levels

In acoustics, the sound pressure level (SPL) is averaged over a given duration to indicate the total sound level. Decibels (dB) are commonly used to indicate the sound pressure level, which is a logarithmic measure of the effective sound pressure about a reference level.

An average rather than a single instantaneous measurement can yield a more meaningful figure when dealing with variable or shifting sound levels. There are various methods for averaging sound pressure levels, and the one selected will rely on the particular needs of the measurement.

$L_n$ Concept

$L_n$ represents the sound pressure level that will exceed N% of the gauging time. 85dB value of L50 means that the sound level will exceed the value of 85dB 50% of the gauging time

$L_eq$ Concept

Not only are the magnitudes of different noise levels taken into account but their decay time duration is also taken into account using the $L_eq$ concept. $L_eq$ can be computed using

{L}<em>p=10\log</em>{10}\frac{1}{N}\displaystyle\sum\limits_{n=0}^N 10^{\frac{L_i}{10}}*t_i

Where $Li$ is the noise level of $i^{th}$ sample, ti is the time duration of $i^{th}$ sample expressed as % of total time.

Limits of Noise Pollution

Area	Limits in dB(A), Leq Day time	Limits in dB(A), Leq Night time
Industrial	75	70
Commercial	65	55
Residential	55	45
Silence Zone	50	40

Noise Reduction

By raising the height of the barrier near the noise source, it can be reduced. Calculation of noise reduction is done using

The practice of lessening undesired or annoying sounds in audio signals or visuals is known as noise reduction. This is a typical task in signal processing, image processing, and audio processing, among other domains. Reducing the influence of unwanted noise is intended to improve the signal’s quality.

Noise Reduction (dB)= ${L}<em>p=10\log</em>{10}(\frac{20H^2}{\lambda R})$

Where 𝜆 is the wavelength of the sound
D distance between the barrier and the receiving point
R is the distance between the source and the wall
H is the height of the barrier wall

Equalization (EQ): Noise reduction can be achieved by adjusting the frequency balance to accentuate or de-emphasize particular frequencies.

Applying filters: such as band-pass, high-pass, or low-pass filters—can assist in attenuating particular frequency ranges linked to noise.

Noise gates: These gadgets efficiently muffle background noise during quiet sections by cutting off the audio transmission when it drops below a predetermined threshold.

Dynamic Range Compression: This method lessens an audio signal’s dynamic range, bringing softer sounds closer to louder ones and potentially lessening the prominence of background noise.

Spectral Subtraction: To improve the signal-to-noise ratio, this technique estimates the noise spectrum and subtracts it from the original signal.

Also Read:- Air Pollution: A Comprehensive Analysis of Harmful Substances Impacting Humans, Animals, and the Environment