Noise Pollution: What is Sound?
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Noise Pollution: What is Sound? Noise can simply be thought of as unwanted sound, or sound that is too loud. Both of these properties are qualitative and depend upon the observer and their situation. Noise pollution is the build-up of noise. So the question is, What is sound? A “sound wave” is a disturbance which moves through the air. It is not that much different from a wave that you see on the water. The difference being that instead of water that moves up and down (oscillates), it is air. This is why you can’t “see” sound. Sound also travels much faster than a water wave. As the graph shows, the period, T, is the time it takes for a particle in the air to move 1 cycle. In other words, if the particle “starts” at the top, it takes T seconds for it to move down and back up again. The frequency is the inverse of period, and is measured in Hertz, or Hz. An important thing to note about sound is that very few things produce “pure tones.” Tuning forks, used by musicians produce pure tones, or a single frequency. Most sound that is produced is made up of all sorts of different sound waves with different frequencies. High frequencies, such as those at 8000Hz, have high pitch sounds like a high squeal. Low frequencies, like the bass in a song, have frequencies around 250Hz. Furthermore, many sounds are not only made up of different frequencies, but each frequency has its own amplitude (loudness). The variation of a sounds’ frequency is called the “spectrum” of the sound.
Noise Pollution and Human Hearing
The human hearing system consists of the head, two ears and the brain. It is a complex system
that can analyze sound frequencies and directions.
Primary parts of the ear include:
Pinna: acts as an acoustic barrier for sound coming from behind
Earcanal: the duct/tube that conducts sound to the eardrum
Eardrum: membrane that translates acoustic waves (ie sound) into mechanical energy
Cochlea: transmits energy into electrical nerve impulses that are sent to the brain and interpreted
as sound!
An average, young human with undamaged hearing is capable of perceiving sounds in the
frequency range of about 20 – 20000Hz.
The decibel (dB) is a measurement of sound, independent of frequency. This does not take into
account human’s sensitivity to different frequencies. For example, humans are much less
sensitive to 100dB of a 100Hz sound compared to a 100dB of 2000Hz sound. The 2000Hz
sound seems much louder to use. To compensate for this, there is a “weighted” decibel scale
called A-weighting, or dBA. When using this scale, 100dBA of 100Hz seems the same to
humans as 100dBA of 2000Hz.Noise Pollution Affecting Our Environment
Noise pollution affects our environment in several ways. Not only can it be annoying for people,
but it can have drastic effects on our basic enjoyment of life. As well, noise pollution can have
devastating effects on wildlife.
Noise is most often defined as unwanted sound, and for humans this can lead to many effects
including:
• Annoyance
• Startle
• Activity interference
• Sleep interruption
• Speech interruption
Productivity is also affected by noise pollution. A study examined children exposed to airport
noise and found that their reading ability and long-term memory was impaired. People working
in noisy office environments have also been found to be less cognitively motivated and have
higher stress levels. (Scott, 2007)
Noise pollution can also lead to the reduction in wildlife populations. There are at least four
ways in which animals are adversely affected by noise pollution (Cornman):
• Hearing loss, resulting from noise levels of 85 dB or greater
• Masking, which is the ability to hear important environmental cues and signals
• Non-auditory physiological effects, such as increased heart rate and respiration
(breathing)
• Behavioral effects, which may result in abandonment of territory by lost reproduction
There are numerous real-life examples of noise impacting wildlife (Fact Sheet). Certain bird
species are flushed from nests in response to noise, their eggs are broken and young are exposed
to injury and predators. Young mammals have been trampled as adults attempt to flee from
aircraft. Mortality rates (ie death rates) of caribou calfs exposed to overflights from aircraft were
significantly higher than those calfs that were not exposed to overflights.Noise Pollution Regulations
Noise can simply be thought of as unwanted sound, or sound that is too loud. Both of these
properties are qualitative and depend upon the observer and their situation. Noise pollution is the
build-up of noise. The Vancouver Noise By-Law tells us what sound levels we can have in
Vancouver. The allowable sound levels (continuous and non-continuous) in activity and quiet
zones are set out below:
RECEIVER
Continuous Non-Continuous
Quiet Activity Quiet / Activity
Day Night Day Night Day Night
Quiet
55 45 60 55 75 70
SOURCE
Activity
60 55 70 65 75 70
Municipal by-laws typically focus on 8 different sources of noise pollution:
1. vocal sounds made by animals owned by residents
2. sounds made my combustions engines
3. Sounds made by vehicles when their tires squeal
4. Sounds made by vehicle horns
5. Sounds made by vehicles which results in banging, clanking, and squeaking (ie pulling a
trailer)
6. Sounds created by construction activity
7. Shouting or voice amplication
8. Burglar or security system alarms
Various Municipal Noise Limits and Times are shown in the table below:
Continuous Noise Non-Continuous Power
Activity zone Quiet zone Equip
Day Nite
Day Nite Day Nite Daytime
Burnaby 65 60 55 45 80 75 87
Delta 65 65
Langley 65 60 55 45 87
New West 60 55 55 45 80 75 87
N. Van 60 55 55 45 80 75 77
Port
65 60 55 45 80 75
Moody
Richmond 65 60 55 45 80 75 82
Vancouver 70 55 55 45 75 70 77
Activity zone: includes industrial, commercial, etc
Quiet zone: generally residential and public areasNoise Pollution and the Workplace
Noise can simply be thought of as unwanted sound, or sound that is too loud. Both of these
properties are qualitative and depend upon the observer and their situation. Noise pollution is the
build-up of noise. We have some statistics on noise pollution from WorkSafe BC which are old,
but still tell a story:
• Claims for hearing-loss related compensation claims cost tax payers over $11/year
• 500,000 people are adversely affected by noise to some extent
• 150,000 workers are subjected to dangerous noise levels
• 80% of companies do not respect the existing laws on health and safety at work
Canada has health regulations on how much noise or sound workers can be exposed to. The
regulations are quite in-depth, and below is a table showing how much sound an employee can
hear in a 24 hour period. This level depends on two things: how loud the sound is, and how long
they hear it for.
A-weighted sound pressure level Max. duration of exposure in hrs, per Max. duration of exposure in
(dBA) 24hr period min, per 24hr period
80 40 (theoretical) n/a
85 16
90 4.0 240
95 1.3 78
100 0.40 24
105 0.13 7.8
110 0.04 2.4
115 0.013 0.8 (47s)
120 0.004 0.24 (14s)
Workers are protected against noise by using hearing protection. There are many types of
hearing protectors available for use. Differences between them depend upon how well they
cancel out noise (attenuate noise), how comfortable they are, and if they are reusable or
disposable. Page 2 of this handout shows pictures of various hearing protectors.
Different protectors also vary by what frequencies they block the best. Some are better at lower
frequencies (125 to 250 Hz), some are better at mid-frequences (500 – 2000 Hz) and some are
better at higher frequencies (4000 – 8000 Hz).
Center Frequency, Hz
125 250 500 1000 2000 4000 8000
Foam Earplugs 20-35 20-35 25-40 25-40 30-40 40-45 35-45
Molded Earplugs
5-20 5-20 10-25 10-25 20-30 25-40 25-40
Earmuffs 5-20 10-25 15-30 25-40 30-40 30-40 25-40
Active noise reduction
headset 15-25 15-30 20-45 25-40 30-40 30-40 25-40You can also read
