As an introduction to this question some basic facts about noise.
Basic noise facts
Noise is typically defined as ‘unwanted sound’. The unit for sound is the Decibel which is a value calculated with logarithms from the pressure to get a scale from 0 to 120 dB where 0 dB is the hearing threshold for a young person with healthy hearing and 120 dB is the pain threshold.
We can state that noise is a type of energy created by vibrations. When an object vibrates it causes moment in air particles. The particles will bump into each other and will generate sound waves, they are ongoing until they run out of energy.
High and low tones are perceived by our hearing due to fast and slow vibrations.
Sound needs a medium to travel and the speed of sound is around 340 meter per second. Examples of typical noise levels:
Due to the nature of the calculation of Decibels we cannot just add them together.
3 dB + 3 dB = 6 dB
10 dB + 10 dB is not 20 dB but 13 dB
The Decibel (sound pressure level) for sound in air is relative to 20 micro pascals (μPa) = 2×10−5 Pa, the quietest sound a human can hear.
The human hearing system
The human hearing system is capable of hearing sounds between 20 Hz and 20000 Hz. Below 20 Hz is called infra sound and above 20000 Hz is called ultrasounds. Both infra- and ultrasound is not audible for us. Elephants however can hear frequencies as low as 14 Hz and bats can hear frequencies up to 80000 Hz.
A special noise weighting for the human perception has been introduced in the 1930’s and called the A-weighted Decibel, dB(A). This was introduced to align the noise levels with the sensitivity and physical shape of the human hearing system.
Basic human hearing system
When sound waves enter the ear, they travel up the ear canal and hit the ear drum, the ear drum will vibrate and the three smallest bones in the human body will transfer these vibrations to the fluid in our inner ear’s sensory organ the cochlea. The sensory hair cells will vibrate which will send nerve impulses to the brain, the brain will translate these impulses for us and we perceive sound!
Dangers of noise
Noise from certain music can be a very pleasurable sound for one person and a horrific noise for another. From this fact we can see that noise is not only an absolute value but also strongly depending on the receiver’s mindset.
However, there are some clear absolute values concerning the danger levels of noise.
- Generally accepted as safe is spending 8 hours per day in an environment not exceeding 80 dB(A)
- NOT safe would be to spend 1 hour in a disco with levels at 100 dB(A) which are easily exceed nowadays
Apart from the obvious hearing loss there are many other issues that can arise from exposure to (too) high noise levels such as:
- Heart disease
- Annoyance – stress
- Immune system – psychosomatic
The positive side to remember is that Noise Induced hearing loss is 100% preventable!!
Governments (especially in Europe) know the actual cost of high noise exposure and they concluded that protecting their citizens from high noise exposure (during working hours, recreation as well as during sleep) is far more effective than dealing with the costs of citizens enduring high noise related illnesses, demotivation, sleep disturbance etc.
They are investing in quiet schools (optimal learning environment), quiet hospitals (patients recover a lot faster in quiet wards), implement city planning to create quite zones.
Of course, they also have strong noise regulations that are being enforced.
Acoustical societies worldwide help to create awareness and leverage noise legislations with governments.
Noise in Asia
I have been living in Asia for the last 15 years and of course I noticed it’s noisy. Noise regulations (if exist at all) are very lenient and mostly not enforced. I’m very happy to see that Acoustical Societies are coming up in Asian countries and can convince governments to invest in setting up proper noise regulations and enforcing them. I’m very happy to be able to contribute to a quieter world by creating more awareness for the dangers of noise!