Did you know that noise pollution can be just as harmful as air pollution? It not only damages hearing but also affects the nervous system and heart. Learn the key concepts related to acoustics and discover how to effectively mitigate the negative effects of noise.

Noise is an annoying, unwanted sound that negatively impacts human health. It can lead to various health issues, including partial or complete hearing loss. Prolonged exposure to intense noise (above 80 dB) can damage the auditory system and affect the nervous system and internal organs. Impulsive and irregular noises are even more harmful to the body. This is why acoustics has developed as a field of science dedicated to measuring noise levels and protecting human health from its adverse effects.

When Does Sound Become Noise? Key Acoustic Parameters

To determine noise levels, several physical quantities are used, with the most important being acoustic pressure, acoustic power, and sound frequency.

Acoustic Pressure

Acoustic pressure is a pressure wave through which sound propagates in a medium, such as air. The human ear perceives these waves as sound. Acoustic pressure is measured in pascals [Pa]. The lowest acoustic pressure that the human ear can detect is 0.00002 Pa, known as the threshold of hearing. The highest pressure the ear can withstand without damage is 20 Pa, referred to as the upper threshold of hearing.

Due to the large difference in acoustic pressure values, a logarithmic scale is used, based on the ratio of actual acoustic pressure (p) to the threshold pressure (p₀). This scale employs the decibel [dB] unit, where 0 dB corresponds to the threshold of hearing, and 120 dB represents the upper hearing threshold.

To convert acoustic pressure to decibels, the following formula is used: L = 20 * log(p/p₀) [dB]

Acoustic pressure decreases with distance from the sound source and depends on room properties and the location of the sound source. It can be measured using a microphone.

Acoustic Power

Acoustic power is the amount of energy emitted by a sound source per unit of time, expressed in watts [W]. Unlike acoustic pressure, acoustic power does not depend on the distance from the sound source or the acoustic properties of the room. Therefore, it is a more universal parameter for comparing different noise sources.

Like acoustic pressure, acoustic power is also expressed on a logarithmic scale. It is not measured directly but is calculated based on acoustic pressure.

Sound Frequency

Frequency (f) defines the number of oscillations of a sound source per unit of time. It is measured in hertz [Hz], where 1 Hz equals one oscillation per second. The higher the number of oscillations, the higher the sound pitch.

The human hearing range spans from 16 Hz to 20,000 Hz. Sounds below 16 Hz are called infrasound, while those above 20,000 Hz are referred to as ultrasound. Frequencies are often divided into eight octave bands: 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz.

Types of Sound Sources

Sound sources vary, but they are generally categorized into three main types: mechanical, aero- and hydrodynamic, and electrical sounds.

• Mechanical sounds occur mainly in manufacturing facilities and where machinery operates. Primary sources include gears, cam mechanisms, chains, gears, bearings, and forging equipment.
• Electrical sounds stem from electric motors and control components of electrical systems.
• Aerodynamic sounds are divided into broadband and discrete sounds. Broadband sounds are associated with turbulence at solid boundaries (e.g., vortices, boundary layers), whereas discrete sounds result from flow irregularities and interactions between various elements in the flow path.

Noise and Ventilation – How to Reduce It?

Ventilation systems also produce noise. When considering fans as noise sources, it is important to remember that the sound level largely depends on the specific device chosen. Factors such as construction type, diameter, and rotational speed significantly influence the declared noise levels. Optimal fan selection, as well as other noise-reducing design methods such as special insulating enclosures or silencers, can help adapt nearly any device to local requirements and reduce noise.

In the case of fans, discrete sounds depend on rotational speed (n) and the number of blades (z). For example, sounds at a frequency of f = n/60 can arise due to rotor imbalance or flow separation, while sounds at a frequency of f = mzn/60 (where m is an integer) result from interactions between rotor blades and guide vanes.

Correction Filters Used in Ventilation

Because the human ear has different sensitivity to various frequencies, noise of the same intensity may be perceived as louder or quieter depending on its frequency.

The most commonly used filter in ventilation is the A-weighting filter, whose attenuation for individual octave bands is shown in the table below:

How Does Noise Affect Health?

Long-term exposure to noise can lead to hearing damage, including permanent hearing loss and tinnitus. Noise also affects the nervous system, increasing stress levels, causing irritability, sleep disturbances, and reduced concentration. Studies show that excessive noise contributes to an increased risk of cardiovascular diseases such as hypertension and heart attacks.

Noise in Schools and Workplaces

Exposure to noise in the workplace can reduce productivity, increase fatigue, and lead to mental health issues such as anxiety or depression. Long-term exposure to noisy environments can also negatively impact children, causing learning difficulties or speech development delays.

How to Protect Yourself from Noise?

Modern life is filled with high-intensity sounds—from busy streets and noisy offices to loud music and electronic devices. Prolonged exposure to noise can lead to numerous health problems, making it essential to know how to protect yourself effectively.

To minimize noise exposure, consider these effective methods:

• Avoiding noise sources – If possible, reduce time spent in noisy environments, such as busy streets or loud workplaces.
• Using hearing protection – In noisy environments, use earplugs or earmuffs, especially at work or concerts.
• Acoustic insulation – In homes and offices, soundproof windows, thicker curtains, carpets, and acoustic panels can help reduce noise.
• Noise-reducing technologies – Active noise-canceling (ANC) headphones help in public spaces, while quiet household appliances minimize everyday noise.
• Practicing hearing hygiene – Take breaks from loud sounds, listen to music at a moderate volume, and have regular hearing checkups.

Implementing these principles in daily life can significantly reduce the negative impact of noise on health and comfort. While completely eliminating noise is impossible, taking a conscious approach to hearing protection helps minimize its harmful effects. Remember, healthy hearing is not just about physical comfort but also mental well-being and overall quality of life.