Background Information

Can You Keep That Noise Down?

Part 1– Terms Used In the Study of Sound

Part 2– Behaviors and Measure of Sound

Part 3–History

Part 4–Uses

Part 5–Soundproofing

Part 6–Effects of Sound

 

Part 1– Terms Used In the Study of Sound

Rarefaction is a region in a sound wave in which the density of the sound medium is less than normal.

Resonance frequency is the frequency at which an object would vibrate naturally if disturbed.

Sound medium is a substance in which sound waves travel. Air, for example, is a sound medium.

Sound quality, also called timbre, is a characteristic of musical sounds. Sound quality distinguishes between notes of the same frequency and intensity that are produced by different musical instruments.

Ultrasound is sound with frequencies above the range of human hearing—that is, above 20,000 hertz.

Wavelength is the distance between any point on a wave and the corresponding point on the next wave.

Acoustics is the science of sound and of its effects on people.

Condensation is a region in a sound wave in which the sound medium is denser than normal.

Decibel (dB) is the unit used to measure the intensity of a sound. A 3,000-hertz tone of 0 dB is the softest sound that a normal human ear can hear.

Frequency of a sound is the number of sound waves that pass a given point each second.

Hertz is the unit used to measure frequency of sound waves. One hertz equals one cycle (vibration, or sound wave) per second.

Intensity of a sound is a measure of the power of its waves.

Loudness refers to how strong a sound seems when we hear it.

Noise is a sound that is unpleasant, annoying, and distracting.

Pitch is the degree of highness or lowness of a sound as we hear it.

Source: The World Book Encyclopedia

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Part 2– Behaviors and Measure of Sound

Sound originates in the vibration of an object. The vibrations make the area around it vibrate also, producing waves which our body translates then as sound. The area in which the sound waves travel is called the sound medium. Because there is no sound medium in space, there is no sound in space. Sound waves travel much like water waves, but in three dimensions. Scientists measure sound in frequency and pitch, wavelength, intensity and loudness and quality. This experiment focuses on the intensity of a sound. The intensity of a sound is a measure of the power of its sound waves. This is measured in decibels. Decibels use a logarithmic scale. For example, 50 dB represents 10 times as much power as 40 dB. Normal conversation is 60 dB, while a large orchestra is 98 dB. Intensity is different than loudness because the pitch of a sound determines how loud it is, unlike intensity , which measures the power of a sound.

 

Part 3–History

One of the earliest researchers of sound was Pythagoras, a Greek philosopher and mathematician, who experimented on the vibration of strings in the 500‘s B.C. Around 400 B.C., a Grecian named Archytas observed faster motion results in high pitched sounds. The Greek philosopher Aristotle suggested that the movement of air carries sound to our ears. Another major discovery of sound wasn’t until the 1600’s when Galileo showed that frequency of sound waves determines the pitch. Many more scientists experimented with sound from then on until Thomas Edison, in 1877, invented a phonograph which could replay a sound. Stereophonic phonographs and discs appeared in 1958 and audio compact discs were introduced in Japan and Europe in 1982.

A recent discovery in acoustics occurred in 2000 when active noise cancellation (ANC) and active structural-acoustic control (ASAC) were actively used. With ANC a speaker produces sound waves that interfere destructively with the waves of unwanted sound. In ASAC, a device called an actuator applies force to an object whose vibration is producing an unwanted sound. This changes the vibration, changing the sound.

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Part 4–Uses

Ultrasound is sound with frequencies above the range of human hearing. Technicians use ultrasound to clean delicate instruments, manufacturers use it to deflect flaws in metals and other materials and physicians use ultrasound to diagnose brain tumours, gallstones and other disorders.

Sonar works when sound waves travel until they reach an object. The sound waves then travel back to their original location. By the speed of the sound waves returning, scientists and geologists can tell how far an area is away from them, such as fishing boats detecting schools of fish.

 

Part 5–Soundproofing

There are two types of silencing sound: through passive absorption and through sound barriers. Passive absorption is when sound passes through an absorptive material, such as fibreglass. Sound is forced to change directions whenever encountering another fibre. Absorbent material work best when there is a reflective material behind them. For a barrier to soundproof, the barrier must have enough mass to stop the energy of the sound waves.

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Part 6–Effects of Sound

Too much exposure to loud noises can cause temporary or permanent hearing loss. Constant noise, even not extremely loud, can cause fatigue, headaches, irritability and tension. For example, if being exposed to an area surrounded with noise from 75 - 84 decibels minor hearing loss may develop, while at 125 decibels a person will feel pain and discomfort, which at 160 decibels a person will have a ruptured ear drum. Saskatchewan Labour Occupation Health and Safety sets regulations for organizations which have loud noises to ensure the lowest possible noise levels in the building and to ensure ear protection is provided to employees. Noise levels must be posted if they are over 80 decibels. Saskatchewan Labour suggests that workers who are exposed to daily average noise levels of 85 decibels and over wear muffs, ear caps or pre-moulded plugs. However, hearing protection improperly fitted may only reduce noise entering the ear by three decibels. Not all noise reduction of hearing protection is properly rated. However, the best noise reduction is through soundproofing the building or work area.

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