Sound VS. Noise

01/03/2020

https://docs.google.com/presentation/d/1w4jDyFM0pq4Xc1hhyIoyrW5kMO676MYZ5Bqyzz9Kn-Y/edit?usp=sharing

Slide 1

Noise vs. Sound

Slide 2

Initial thought:

What is the difference between noise and sound?
How does this relate to music?
How does this relate to the environment we live in everyday?

Slide 3

What is sound?

Acc. to the Canadian Centre for Occupational Health & Safety, "Sound is what we hear."
More technically,

"Sound is a form of energy that is transmitted by pressure variations which the human ear can detect. When one plays a musical instrument, say a guitar, the vibrating chords set air particles into vibration and generate pressure waves in the air. A person nearby may then hear the sound of the guitar when the pressure waves are perceived by the ear. Sound can also travel through other media, such as water or steel.

Slide 4

"Sound is produced by vibrating objects and reaches the listener's ears as waves in the air or other media. When an object vibrates, it causes slight changes in air pressure. These air pressure changes travel as waves through the air and produce sound. To illustrate, imagine striking a drum surface with a stick. The drum surface vibrates back and forth. As it moves forward, it pushes the air in contact with the surface. This creates a positive (higher) pressure by compressing the air. When the surface moves in the opposite direction, it creates a negative (lower) pressure by decompressing the air. Thus, as the drum surface vibrates, it creates alternating regions of higher and lower air pressure. These pressure variations travel through the air as sound waves"

Slide 5

Slide 6

"Table 1 lists the approximate velocity of sound in air and other media. In gases, the higher the velocity of sound, the higher the pitch will be (Remember the "Mickey Mouse" sound when people talk after inhaling helium gas?)."

Table 1
Estimated Speed of Sound in Common Materials

Medium

Sound
Velocity
(ft/s)

m/s

Air, dry (0°C and 760 mm Hg)

1,100

330

Wood (soft - along the fibre)

11,100

3,400

Water (15°C)

4,700

1,400

Concrete

10,200

3,100

Steel

16,000

5,000

Lead

3,700

1,200

Glass

18,500

5,500

Hydrogen (0°C and 760 mm Hg)

4,100

1,260

Slide 7

"The hearing mechanism of the ear senses the sound waves and converts them into information which it relays to the brain. The brain interprets the information as sound. Even very loud sounds produce pressure fluctuations which are extremely small (1 in 10,000) compared to ambient air pressure (i.e., atmospheric pressure). The hearing mechanism in the ear is sensitive enough to detect even small pressure waves. It is also very delicate: this is why loud sound may damage hearing."

Slide 8

"What is noise?

Sound is what we hear. Noise is unwanted sound. The difference between sound and noise depends upon the listener and the circumstances. Rock music can be pleasurable sound to one person and an annoying noise to another. In either case, it can be hazardous to a person's hearing if the sound is loud and if he or she is exposed long and often enough."

Slide 9

Questions: (to the class)

What are different sounds you enjoy?
Which do you despise? Why?
What feelings are attached to those sounds?

Slide 10

"What are some properties of noise that can be measured?

The properties of noise which are important in the workplace are:
frequency
sound pressure
sound power
time distribution"

Slide 11

"What are pitch and frequency?

Frequency is the rate at which the source produces sound waves, i.e. complete cycles of high and low pressure regions. In other words, frequency is the number of times per second that a vibrating body completes one cycle of motion. The unit for frequency is the hertz (Hz = 1 cycle per second: Figure 1 shows one cycle from an air compression to a minimum pressure and back to a maximum pressure).
The Harvard Dictionary of Music defines the pitch as a "stretch of sound whose frequency is clear and stable enough to be heard as not noise". The Oxford Dictionary defines pitch as "the quality of a sound governed by the rate of vibrations producing it; the degree of highness or lowness of a tone." Since the pitch is determined mostly by frequency, it is usually identified with it. The pitch depends also, in a lower degree, on the sound level and on the physiology of the auditory system.
Low pitched or bass sounds have low frequencies. High-pitched or treble sounds have high frequencies. A healthy, young person can hear sounds with frequencies from roughly 20 to 20,000 Hz. The sound of human speech is mainly in the range 300 to 3,000 Hz."

Slide 12

"What is sound pressure?

Sound pressure is the amount of air pressure fluctuation a noise source creates. We "hear" or perceive sound pressure as loudness. If the drum in our example (Figure 1) is hit very lightly, the surface moves only a very short distance and produces weak pressure fluctuations and a faint sound. If the drum is hit harder, its surface moves farther from its rest position. As a result, the pressure increase is greater. To the listener, the sound is louder.
Sound pressure also depends on the environment in which the source is located and the listener's distance from the source. The sound produced by the drum is louder two metres from the drum if it is in a small bathroom, than if it is struck in the middle of a football field. Generally, the farther one moves from the drum, the quieter it sounds. Also if there are hard surfaces that can reflect the sound (e.g., walls in a room), the sound will feel louder than if you heard the same sound, from the same distance, in a wide-open field.
Sound pressure is usually expressed in units called pascals (Pa). A healthy, young person can hear sound pressures as low as 0.00002 Pa. A normal conversation produces a sound pressure of 0.02 Pa. A gasoline-powered lawn mower produces about 1 Pa. The sound is painfully loud at levels around 20 Pa. Thus the common sounds we hear have sound pressure over a wide range (0.00002 Pa - 20 Pa)."

Slide 13

"What is a sound pressure level?

It is difficult to work with the broad range of common sounds pressures (0.00002 Pa - 20 Pa). To overcome this difficulty we use decibel (dB, or tenth (deci) of a Bel)). The decibel or dB scale is more convenient because it compresses the scale of numbers into a manageable range.
The decibel is named after Alexander Graham Bell, the Canadian pioneer of the telephone who took great personal interest in the problems of deaf people.
Sound pressure converted to the decibel scale is called sound pressure level (Lp). Appendix A gives a detailed explanation of decibels and sound pressure levels. Figure 2 compares sound pressures in pascals and sound pressure levels in decibels (dB). The zero of the decibel scale (0 dB) is the sound pressure of 0.00002 Pa. This means that 0.00002 Pa is the reference sound pressure to which all other sound pressures are compared on the dB scale. This is the reason the decibels of sound are often indicated as dB re 0.00002 Pa."

Slide 14

Slide 15

"What kinds of noise are there?

Noise can be continuous, variable, intermittent or impulsive depending on how it changes over time. Continuous noise is noise which remains constant and stable over a given time period. The noise of boilers in a power house is relatively constant and can therefore be classified as continuous.
Most manufacturing noise is variable or intermittent. Different operations or different noise sources cause the sound changes over time. Noise is intermittent if there is a mix of relatively quiet and noisy periods. Impulse or impact noise is a very short burst of loud noise which lasts for less than one second. Gun fire or the noise produced by punch presses are examples of such noise."

Slide 16

"What are A-weighted decibels?

The sensitivity of the human ear to sound depends on the frequency or pitch of the sound. People hear some frequencies better than others. If a person hears two sounds of the same sound pressure but different frequencies, one sound may appear louder than the other. This occurs because people hear high frequency noise much better than low frequency noise.
Noise measurement readings can be adjusted to correspond to this peculiarity of human hearing. An A-weighting filter which is built into the sound measuring instrument de-emphasizes low frequencies or pitches. Decibels measured using a sound meter equipped with this filter are A-weighted and are called dB(A). Legislation on workplace noise normally gives exposure limits in dB(A). Table 2 lists examples of typical noise levels.
A-weighting serves two important purposes:
gives a single number measure of noise level by integrating sound levels at all frequencies
gives a scale for noise level as experienced or perceived by the human ear"

Slide 17

Table 2
Typical Noise Levels

Noise Source

dB(A)

pneumatic chipper at 1 metre

115

hand-held circular saw at 1 metre

115

textile loom

103

newspaper press

power lawn mower at 1 metre

diesel truck 50 km per hour at 20 metres

passenger car 60 km per hour at 20 metres

conversation at 1 metre

quiet room

Slide 18

"Why is noise an important workplace hazard?

Noise is one of the most common occupational health hazards. In heavy industrial and manufacturing environments, as well as in farms, cafeterias, permanent hearing loss is the main health concern. Annoyance, stress and interference with speech communication are the main concerns in noisy offices, schools and computer rooms.
To prevent adverse outcomes of noise exposure, noise levels should be reduced to acceptable levels. The best method of noise reduction is to use engineering modifications to the noise source itself, or to the workplace environment. Where technology cannot adequately control the problem, personal hearing protection (such as ear muffs or plugs) can be used. Personal protection, however, should be considered as an interim measure while other means of reducing workplace noise are being explored and implemented.
As a first step in dealing with noise, workplaces need to identify areas or operations where excessive exposure to noise occurs."

Slide 19

"How can I tell if my workplace is too loud?

If you answer yes to any of the following questions, the workplace may have a noise problem.
Do people have to raise their voices?
Do people who work in noisy environments have ringing in their ears at the end of a shift?
Do they find when they return home from work that they have to increase the volume on their car radio higher than they did when they went to work?
Does a person who has worked in a noisy workplace for years have problems understanding conversations at parties, or restaurants, or in crowds where there are many voices and "competing" noises?
If there is a noise problem in a workplace, then a noise assessment or survey should be undertaken to determine the sources of noise, the amount of noise, who is exposed and for how long."

Slide 20

99% Invisible - podcast (00:25-03:30)

Slide 21

Foghorns in the San Francisco Bay

Slide 22

San Francisco Air Raid Siren

Slide 23

Bibliography

99pi. "Sound and Health: Cities." 99% Invisible, 16 May 2019, 99percentinvisible.org/episode/sound-and-health-cities/.

Andrés, Lisi. "Barcelona Symphony Orchestra." OBC, 28 Sept. 2017, www.obc.es/en/26024.

Bharadwaja H, Sameera. "How Do We Perceive Sound?" Quora, 25 Feb. 2015, www.quora.com/How-do-we-perceive-sound.

Canadian Centre for Occupational Health. "Noise - Basic Information." Canadian Centre for Occupational Health and Safety, 26 Nov. 2019, www.ccohs.ca/oshanswers/phys_agents/noise_basic.html.

Environmental Protection Department. The Government of the Hong Kong SAR. . "Sound And Noise: Index." Sound and Noise, unknown, www.epd.gov.hk/epd/noise_education/web/ENG_EPD_HTML/m1/index.html.

"Noise." Wikipedia, Wikimedia Foundation, 17 Dec. 2019, en.wikipedia.org/wiki/Noise.

"Golden Gate Fogged in with Fog Horns." YouTube, YouTube, 18 Mar. 2011, www.youtube.com/watch?v=iSHmAXMA_hQ&t=95s.

Olemarskan. "San Francisco Air Raid Siren." YouTube, YouTube, 16 May 2017, www.youtube.com/watch?v=RZbcnpdy9UE.