What Is Sound And How Do Humans Detect It?

Things around us produce sound when they are either moving or shaking. We call this shaking movement vibration [1]. Think of the strings of a violin, or a car passing by. Even your voice is the result of movements and vibrations. This movement is the reason that sound is also a form of energy, similar to electricity or heat, for example.

The human ear is made up of three different parts, the outer ear, the middle ear, and the inner ear (Figure 1). When something vibrates, air molecules travel through the air as sound waves. Sound waves are detected by our ears, which convert the waves into electrical pulses that travel to our brains. Sound arriving at the outer ear causes vibration of a small piece of skin-like tissue called the tympanic membrane (also known as the eardrum). The tympanic membrane is connected to a set of three small bones, the ossicles, that make up the middle ear. These bones allow vibrations in the eardrum to act on a tiny organ in the inner ear called the cochlea. The changing pressure in the cochlea caused by these vibrations is then sent to the brain in the form of nerve signals.

Our brains figure out what these nerve signals mean. We can distinguish between the various parts of a sound, such as the pitch (how high or low the sound is) and the intensity (how loud or quiet the sound is). We are most likely to notice sounds that change in intensity and pitch. A siren is a good example of a sound that has been designed with this in mind, to get our attention.

When Does Sound Turn Into Noise?

The simplest definition of noise is any sound that we do not want to hear, often sounds we find annoying or disturbing. This definition makes it immediately clear that noise is a somewhat individual judgment, and one that depends on context. For example, your favorite music might sound lovely to you, but might feel like noise to someone else. Even if the other person normally likes the same bands as you, they might perceive your music as noise if you play it very loudly late at night when they are trying to sleep!

Scientists divide noise into three main groups, or categories. These categories make it easier to identify which types of noise affect us the most (Figure 2). Continuous noise is the type of noise that occurs without interruption, such as the noise produced by machinery, a fan running non-stop, or a gently crackling fire. As the intensity and pitch of sound remain basically the same, our brains tend to adapt and become less sensitive to continuous noise. As we will discuss later, this type of noise may sometimes be beneficial. Intermittent noise often includes fast changes in the noise level, such as an aircraft or a single vehicle driving by in a normally quiet area. This change in noise level tends to trigger the brain and can potentially disturb or even annoy us [2]. Impulsive noise is characterized by a sharp and sudden increase in noise level, such as that caused by fireworks or an explosion. Experiments have shown that this type of noise can cause us the greatest annoyance [2].

Noise Pollution And Our Health

If we do not want to see something, we can close our eyes. But unfortunately, we cannot close our ears! This makes it difficult to protect ourselves from unwanted sounds. People living in large cities are bombarded with noise from road traffic, passing aircraft, sirens, construction, and general human activity. Unwanted sounds like these are often called noise pollution. Through many years of research, scientists have learned that long-term exposure to noise can make us unwell. It can increase our stress levels and reduce our ability to concentrate and communicate. Noise disturbance also affects how well we sleep, which can lead to more serious problems such as heart failure or stroke [3].

To attempt to address these problems, scientists and engineers have come up with recommended noise targets for different types of buildings, including our homes, hospitals, schools, and workspaces. With the help of these targets, acoustic engineers aim to design buildings that are pleasant to be in. Their acoustic design protects us from too much harmful noise.

Although our buildings are generally designed to protect us from external noise, what about noise that is actually generated indoors? When does this indoor noise become a serious issue?

Noise In Hospitals

Hospitals are typically occupied by the most vulnerable groups of people, such as the elderly, sick people, or people with physical disabilities. These groups are often less able to cope with stress than healthy people are. Evidence suggests that people recover better in a peaceful and relaxing atmosphere, so it would be natural to assume that hospital buildings are good at ensuring noise is kept to a minimum [4]. However, sound scientists have discovered that the noise generated from everyday activities in hospitals far exceeds recommended levels. General patient noise, visitor and staff conversations, medical equipment, alarms, televisions, trolleys, phones, and doors all create a highly noisy environment that is difficult to control.

Despite the attempts of many hospitals to reduce noise levels with “quiet please” signs, patients are often exposed to various types of noises at random hours, including at night. In some cases, the noise levels in some hospital rooms are similar to very loud music through headphones and are almost loud enough to damage patients’ hearing! As a result of these disruptions, 40% of hospital patients in the United Kingdom have reported that they found it difficult to sleep, which made them feel annoyed and stressed [5]. This means that noise in hospitals can make people who are already sick even sicker, which means they take longer to recover. However, this does not need to be the case. There are methods that can be used to reduce unnecessary noise in hospitals and protect patients’ health.

What Can Be Done?

Noise can be controlled in three main ways. We can control noise at its source—the place it comes from. Or we can control the noise as it travels—on its path (through the air, for example). Finally, we can control noise where it is received by our ears (Figure 3). Although controlling noise at its source is often considered to be the most desirable, it may not always be possible.

When we think about the problem of noisy hospitals, there are several possible approaches that could be used to protect patients from noise. To control noise at the source level, hospitals could provide training to staff to keep noise low, and they could inform patients and visitors of the importance of being quiet. Hospitals could also avoid unnecessary noise by ensuring hospital equipment, such as trolleys, beds, and doors, is kept in good condition. To control noise at the path level, hospitals could use sound-absorbing panels in patient rooms. They could also use loudspeakers in the ceiling to produce constant background noise, similar to the continuous noise discussed earlier. This type of noise can help patients to be less disturbed by other noise sources. This process is often called sound masking [5]. Finally, to control noise at the receiver level, hospitals could give patients earplugs to help minimize disturbance and allow them to sleep further away from noisier areas, such as reception.

Conclusion

Our ability to hear allows us to communicate with one another, to listen to our favorite music, and to protect ourselves from danger. But too much noise pollution is very harmful for our health. Many patients in our hospitals find it hard to sleep because of high noise levels, which can increase the length of time it takes for them to recover. While there are ways to help reduce the impact of noise in our world, there is a lot more to be done to deal with the issue. We hope that, as our world and technology develop, new ways of controlling noise will be invented to help us protect ourselves and others from the harmful effects of noise pollution.

Glossary

Vibration: ↑ A periodic motion back and forth or from side to side.

Pitch: ↑ Allows to judge sounds as “high” and “low.”

Intensity: ↑ The energy carried in sound waves.

Continuous Noise: ↑ Remains constant and stable over a given time period.

Intermittent Noise: ↑ Stops and starts rapidly.

Impulsive Noise: ↑ Rapid and loud noise of short duration 7.

Noise Pollution: ↑ Regular experience of noise levels that can be harmful for humans or other living organisms.

Sound Masking: ↑ Is the generation of certain sounds to cover or partially cover other sounds

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.