Sounds can be interpreted as music, a story, a joke, a warning or an endless array of other possible signals. Sound can often bring us great pleasure, but it can also annoy us, or those around us. People have varying tolerance levels for sounds. If the sound goes beyond the tolerance level, it is classified as noise, but this depends on the characteristics of the particular person as well as the sound. For example, a group of people might enjoy playing loud rap music at 3a.m. The same sounds might not be appreciated by their neighbours! Likewise, a crying baby needs to able to make its parents hear when it requires feeding – other members of the family might be annoyed by the same sounds.

Where does noise come from? Almost every aspect of modern life generates noise – industrial processes, construction, office work and even home and leisure activities. Industrial production and construction are rapidly increasing in many countries and this brings with it an increase in industrial or ‘occupational’ noise. If we expose ourselves to extreme noise levels, then damage to our hearing can easily occur. Ultimately this could lead to severe deafness and to exclusion and isolation from society. Therefore, it is essential that we take good care of our hearing.

Noise or sound is created by alternate compression and decompression of particles of the air. This causes the air pressure to fall and rise in the form of waves. Frequency (pitch) and intensity (loudness) are the two characteristics of sound.

Frequency

Frequency is the number of times that the air is compressed and decompressed in a second, and is measured in cycles per second, or Hertz (Hz). Low frequency produces a low pitched, bass sound. High frequency produces a high pitched, whistle sound. Human ears respond to frequencies between 20Hz and 20,000Hz. The human voice produces frequencies between 500Hz and 2,000Hz. Below 20Hz and above 20,000 Hz sound cannot be heard but it can still be harmful. The ear is most sensitive to sounds between 1000 and 4000Hz.

The infra-sounds and the ultra-sounds, although not heard by humans, produce feelings of nausea, giddiness and headache in people exposed to them. Infra-sounds are the subtlest and can occur in aeroplanes and other vehicles. Noise from heavy road vehicles can penetrate the walls of houses.

Deafness

The main effect of noise is the development of deafness, especially when you are exposed to high levels of continuous noise, for example, during working hours. This may result in ‘noise-induced occupational deafness’. There is no cure and no treatment for deafness. Damage to your hearing is permanent, and will never get better.

Occupational deafness is a gradual process of reduction of hearing ability associated with damage to the cochlea. Occupational deafness does not occur accidentally; it is a result of not reducing exposure to noise, for example, by moving out of a noisy environment or wearing hearing protection. The initial loss of hearing occurs at frequencies above those involved in speech (500-2,000Hz) and consequently considerable loss can occur before the effect becomes noticeable to you. The obvious danger is that considerable damage may have occurred to the hearing mechanism before you become aware of it, and in later life, this deafness will become worse because of the natural effects of the aging processes.

Noise and performance

Noise causes fatigue and loss of concentration and efficiency, resulting in a decrease in work output and an increase in the number of mistakes made. Work involving learning is more susceptible to disruption from noise than routine work. This could be of importance to a school leaver training on-the-job in a noisy work environment.

Speech comprehension

The comprehension of speech is affected by both the sound level of the background noise and the sound level of the voice itself. The average intensity of a human voice in a room at a distance of one metre lies within the following ranges:

Conversation   60-65dB(A)

Dictation           65-70dB(A)

Calling out        80-85dB(A)

The general background noise level must be at least 10dB(A) below these levels if the sound of the voice is to be heard clearly.

Noise generated by humans, such as voices, dropping of objects, noisy children, can be a strong irritant. Background noise, determined by the environment around you can also be an irritant. Proximity of schools, operation of street cleaning equipment or refuse collection, and traffic noise can all contribute to increased noise exposure. In 1994 it was estimated that 22% of residents in Europe (77 million people) were exposed to transportation noise of more than 65dB(A); this level is considered to be unacceptable. In general, different residential areas have different background noise and may range from ‘very quiet suburban’ to ‘very noisy residential’.

Many leisure activities have become major sources of noise and hazards to hearing. Levels in night clubs can exceed 100dB(A). Most visitors are exposed to this only for a few hours per week, but DJs, musicians, bar and security staff are working in this all the time and may be at risk of damage to their hearing.

The World Health Organisation (WHO) provides some guidance on acceptable levels of noise in the community.

Specific environment	Health effects	Target level (dB(A))
Outdoor living area	Serious annoyance, daytime and evening	55
	Moderate annoyance, daytime and evening	50
Indoor living area	Speech intelligibility and moderate annoyance, daytime and evening	35
Inside bedrooms or hospital ward rooms	Sleep disturbance, night time	30
Outside bedrooms	Sleep disturbance (window open)	45
School classrooms	Speech intelligibility, disturbance of information extraction, message communication	35
Hospital treatment rooms	Interference with rest and recovery	as low as possible
Industrial, commercial, shopping and traffic areas	Hearing impairment	70
Ceremonies, festivals and entertainment events	Hearing impairment	100
Public address	Hearing impairment	85
Music through headphones	Hearing impairment	85