People use sound all the time. We rely on sounds to communicate. Unexpected noises may warn us of danger. The sounds we hear tell us a lot about our surroundings.
What is sound?
Sound is a vibration or wave of air molecules caused by the motion of an object. The wave is a compression wave where the density of the molecules is higher. This wave travels through the air at a speed dependent on the temperature. A sound wave contains energy, which in turn means it can make things move. However, if the wave strikes something solid, the wave will bounce back -- an echo
Sound waves can travel through most types of matter. We are most familiar with sound moving through air, but it can move through other gases, as well as liquids and solids. In fact, the density of the universe was so great during its first 300,000 years that sound waves were able to ripple throughout it.
How the ears work?
Ear connects sound waves and pass information about them to the brain. The bigger the ears the more sound energy they can connect. The inner ear mechanism also helps maintain balance and the orientation of the head. We tend to think that sounds we can hear are the only sounds that exist. But a dog or horse's ears may pick up when we hear nothing though ear are sensitive, but they cannot hear all the sounds that come through the air. Our ears have a limited ability to detect sounds. A typical person can hear sounds from about 20Hz to 20,000Hz.Sound with frequencies lower than 20Hz do not simulate the ear; so we are unaware of them. Yet they do exist and some animals may be able to detect them.
What is Noise?
In common use, the word noise means any unwanted sound. In both analog and digital electronics, noise is an unwanted perturbation to a wanted signal.
Noise perception is subjective; one person's maximum-volume music listening pleasure might be another's unbearable noise. Factors such as the magnitude, characteristics, duration, and time of occurrence may affect one's subjective impression of the noise.
How Loud is Too Loud
Noise is measured in dBA, which is a decibel scale modified to take into account the sensitivity of human ears to different pitches of sound. It is a logarithmic scale, which means that an increase or decrease of 3 dBA represents a doubling or halving of intensity, the energy it contains. So, for example, 73 dBA is twice as intense as 70 dBA. However, due to the way we hear sounds; a person with normal hearing will only think a sound has doubled in loudness when it is ten times more intense. For example: 80dBA will only sound twice as loud as 70dBA despite actually having ten times as much energy.
An average conversation will reach around 60 dBA while a busy street can peak at 80 to 90 dBA. Generally, exposures to sound levels below 80dBA are unlikely to cause any hearing damage. Prolonged exposure to sounds over 80 dBA can damage your hearing and the risk increases as the sound level increases. So at 140 dBA noise causes immediate injury to almost any unprotected ear.
As a general guide, if you have to shout to make yourself heard by someone two
meters away the noise level could be dangerous. Although there are laws about acceptable levels of noise in different situations, it is impossible to set an objective noise level that is safe for all. However, no two people will have an identical tolerance to noise. Research suggests that a genetic predisposition towards hearing loss is an important factor.
How Does Noise Damage Hearing
Repeated exposure to excessive noise can kill the hair cells and damage the hearing nerve making them unable to work properly and resulting in a permanent hearing loss. This is called a ‘sensorineural’ hearing loss. Someone with noise-induced hearing loss will first notice a difficulty hearing the high-pitched sounds that are important in being able to hear people talk. So although some sounds will remain reasonably clear - like people’s actual voices - the words they are saying will be distorted. For example, you may be watching a TV programme and be able to hear that the characters are talking, but what they are saying will be hard to understand. Naturally, this makes trying to understand a single person in a noisy background or with other people speaking very difficult and frustrating.
However, it is possible to recognize signs of hearing damage quite early. If you have difficulty hearing people or you suffer tinnitus on leaving a noisy environment, your hearing may well be damaged. Repeated exposure to noise at a high level can leave you with a permanent hearing loss or tinnitus.
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