Sound Explained

Many people never give sound a second thought and it’s something we take for granted. However, the science of sound is a fascinating topic, explaining interesting facts such as why animals have different hearing abilities from humans, and why our hearing changes as we age.

According to the laws of physics, sound is a vibration creating an audible wave of pressure. This is transmitted by a medium such as a liquid, gas or solid. It is defined as a wave motion in air or another media, known as a “stimulus”.

In terms of human physiology, we can hear sounds because we receive the waves and they are perceived by the brain. This is known as a “sensation” and is defined as an excitation of our hearing mechanism.

Human beings can hear sound waves that have a frequency of between 20 Hz and 20 kHz. Any sound with a frequency higher than 20 kHz is called ultrasound, while a frequency lower than 20 Hz is known as infrasound. Humans can’t hear these sounds, although animal species have different hearing ranges.

Why can animals hear sounds that we can’t?

Dogs’ hearing is more sophisticated than ours, so that when a dog whistle (a popular training aid) is used the dog will respond, even though humans can’t hear it at all.

This is because dogs can hear sounds of up to 50,000 Hz (50,000 vibrations per second) when we can’t. A dog whistle emits sounds of greater than 20,000 Hz, so the dog will respond, while it appears silent to us.

Dogs’ ears are controlled by 18 muscles, compared with human ears which have only six. Hence dogs can rotate and tilt their ears to channel the sound into their inner ear more effectively. In addition, some dog breeds’ ears are shaped so they actually amplify sounds.

A dog’s ear canal is longer than a human’s, with more muscles that enable it to fine-tune its position and localise sound – so they can hear it from farther away and more accurately. A cat’s hearing is even better than a dog’s, as felines have 30 ear muscles which adapt to differentiate between sounds.

When you’re wondering how your cat knows you’ve opened the kitchen cupboard door to get their treats out, even if they’re in the lounge, it’s because they’ve heard you and recognise the sound!

Why does our hearing deteriorate as we get older?

Our hearing deteriorates with age as a result of a change in the tiny hair cells within our inner ear – a medical condition known as presbycusis. The hair cells detect sound waves, converting them into nerve signals. The brain then interprets the signals as sound.

When the hair cells are damaged or die, hearing loss occurs. These hair cells don’t regrow and the damage is permanent. Although there isn’t a single known cause of age-related hearing loss, experts say it occurs as a result of changes to the inner ear as we grow older.

It can occur faster if you have a family history of hearing loss, as it may be in your genes, or if you were subject to loud noises when you were younger, such as loud rock concerts, or a noisy job where you didn’t have the correct hearing protection.


When does sound become noise?

Any sounds that you don’t particularly want to hear are referred to as noise and can be a nuisance. Four different types of noise are defined:

  • Continuous noise: This is any noise that emits continuously without interruption, such as from factory machinery, ventilation or heating systems.
  • Intermittent noise: This is defined as a noise level that continually increases and decreases, such as factory machinery that operates in cycles, or more rapid increases such as a train passing by, or a loud aircraft overhead.
  • Impulsive noise: The construction and demolition industry is a major cause of impulsive noise. It is a sudden burst of noise (such as an explosion or the sound of a pile driver) which can startle you.
  • Low-frequency noise: This is a type of noise that makes up our daily life, such as the low hum of power plants. It can spread for miles around if it isn’t properly reduced at source.


What is acoustics?

Acoustics is a science that focuses on the study of sound, vibration, ultrasound and infrasound. Scientists working in the field of acoustics are called acousticians, while acoustical engineers are those who work in the field of acoustic engineering.

These terms are not to be confused with audio engineers, who are involved in the recording, mixing and reproduction of sounds.

Applications of acoustics are found in just about every aspect of modern society, including architectural acoustics, aeroacoustics, electro-acoustics, environmental noise, musical acoustics, noise control, vibrations and other fields.

Sound Planning provides professional noise and vibration consultancy services. With more than 35 years’ experience in acoustic solutions, we specialise in the design and supply of noise control products and sound enclosures in a variety of sectors. We offer a complete turnkey package for all your noise control requirements.

For a quieter life, give us a call!


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