Reflex loudspeaker animation

What is Sound[edit | edit source]

Sound is produced when materials vibrate. Energy in sound waves can be transmitted from one substance to another. The air molecules are pressed together when the vibrating object moves forward and pushes against them. Compression, is when molecules are pressed together. Rarefaction, where molecules are spread out. And one compression and one rarefaction together make up wavelength.

Sound travel faster through liquids than through gases, and even faster through solids. The closer the molecules are in a substance the faster sound travel through that substance. The speed of sound is independent of its frequency.

  • Sounds travels in longitudinal waves.
  • Sound waves have frequency; the pitch of the sounds goes up or down.
  • The amplitude of a sound determines it’s volume.
  • Tone is a measure of the quality of a sound wave.

How Does Sound Travel?[edit | edit source]

Sound travels through the air in the form of vibrations. These vibrations cause particles of air to compress together and this causes the air around them to move in such a way that they are driven in waves away from the source.

The way that sound travels is an oft discussed topic in basic science for younger children. Many kids can easily identify a source of sound and understand how the ear detects it, but struggle to understand the process in between.

Air molecules cause vibration from a drum when it is banged

Just like light, sound travels in waves caused by air molecules that vibrate. If a drum is banged the air molecules around the drum vibrate, and these vibrations cause air molecules slightly further away to shake in turn. The process repeats until the vibrations lessen and the sounds begin to dissipate.

A simple toy slinky is an excellent tool for demonstrating how sound waves work to budding scientists. Stretching a slinky across a desk and pushing one end rapidly illustrates the compression that causes air particles to bunch together as the wave is sent along the spring. The parts of the spring representing air molecules do not move and simply vibrate, while the wave noticeably bounces back towards the end that was pushed, representing an echo.

The Doppler Effect is an increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other. The effect causes the sudden change in pitch noticeable in a passing siren, as well as the redshift, is seen by astronomers. Astronomers use Doppler shifts to calculate precisely how fast stars and other astronomical objects move toward or away from Earth. For example, the spectral lines emitted by hydrogen gas in distant galaxies is often observed to be considerably redshifted.

The Doppler effect can be described as the effect produced by a moving source of waves in which there is an apparent upward shift in frequency for observers towards whom the source is approaching and an apparent downward shift in frequency for observers from whom the source is receding. It is important to note that the effect does not result because of an actual change in the frequency of the source.
The Doppler effect can be observed for any type of wave – water wave, sound wave, light wave, etc. We are most familiar with the Doppler effect because of our experiences with sound waves. Perhaps you recall an instance in which a police car or emergency vehicle was traveling towards you on the highway. As the car approached with its siren blasting, the pitch of the siren sound (a measure of the siren’s frequency) was high; and then suddenly after the car passed by, the pitch of the siren sound was low. That was the Doppler effect – an apparent shift in frequency for a sound wave produced by a moving source.

Suppose that there is a happy bug in the center of a circular water puddle. The bug is periodically shaking its legs in order to produce disturbances that travel through the water. If these disturbances originate at a point, then they would travel outward from that point in all directions. Since each disturbance is traveling in the same medium, they would all travel in every direction at the same speed. These circles would reach the edges of the water puddle at the same frequency. An observer at point A (the left edge of the puddle) would observe the disturbances to strike the puddle’s edge at the same frequency that would be observed by an observer at point B (at the right edge of the puddle). In fact, the frequency at which disturbances reach the edge of the puddle would be the same as the frequency at which the bug produces the disturbances. If the bug produces disturbances at a frequency of 2 per second, then each observer would observe them approaching at a frequency of 2 per second.

Sonic Boom

A sonic boom is a sound linked with the shock waves created by an object traveling through the air faster than the speed of sound. Sonic booms produce massive amounts of sound energy, sounding much like an explosion. The crack of a supersonic bullet passing overhead is an example of a sonic boom in miniature.

If a boat travels faster than the waves can spread through water, then the waves “can’t get out of the way” of the boat fast enough, and they form a wake. A wake is a larger single wave. It is formed out of all the little waves that would have spread ahead of the boat but could not.

When an airplane travels through the air, it produces sound waves. If the plane is traveling slower than the speed of sound (the speed of sound varies, but 700 mph is typical through the air), then sound waves can broadcast ahead of the plane. If the plane breaks the sound barrier and flies faster than the speed of sound, it produces a sonic boom when it flies past. The boom is the “wake” of the plane’s sound waves. All of the sound waves that would have normally broadcasted ahead of the plane are combined together so at first, you hear nothing, and then you hear the boom they create.

It is just like being on the shore of a smooth lake when a boat speeds past. There is no disturbance in the water as the boat comes by, but eventually, a large wave from the wake rolls onto the shore. When a plane flies past at supersonic speeds the exact same thing happens, but instead of the large wake wave, you get a sonic boom.

Sympathetic and Forced Vibrations

  • Sympathetic Vibrations: All objects have a natural frequency of vibrations. Therefore, sound waves form one object vibrating at the natural frequency of a second object can cause the second object to vibrate without physically touching.
  • Forced Vibrations: One vibrating object causing another object to vibrate because they are in physical contact.

Speed of Sound

The speed of sound depends on the medium that the waves pass through, and is a fundamental property of the material. The first significant effort towards the measure of the speed of sound was made by Newton. He believed that the speed of sound in a particular substance was equal to the square root of the pressure acting on it (STP) divided by its density.

  • The speed of sound at sea level is equivalent to 340.29 m/s, in dry air at 20 C the speed of sound is 343 m/s, 2.9 in kilometers and 4.69 in miles.
  • The speed varies depending on the atmospheric conditions the most important factor is the temperature.

Perception of Sound

A distinct use of the term sound from its use in physics is that in physiology and psychology, where the term refers to the subject of perception by the brain. The field of psychoacoustics is dedicated to such studies. Historically the word “sound” referred exclusively to an effect in the mind. This meant (at least in 1947) the correct response to the question: “if a tree falls in the forest with no one to hear it fall, does it make a sound?” was “no”. However, owing to contemporary usage, definitions of sound as a physical effect are prevalent in most dictionaries. Consequently, the answer to the same question (see above) is now “yes, a tree falling in the forest with no one to hear it fall does make a sound”.
The physical reception of sound in any hearing organism is limited to a range of frequencies. Humans normally hear sound frequencies between approximately 20 Hz and 20,000 Hz (20 kHz). The upper limit decreases with age. Sometimes sound refers to only those vibrations with frequencies that are within the hearing range for humans or sometimes it relates to a particular animal. Other species have different ranges of hearing. For example, dogs can perceive vibrations higher than 20 kHz but are deaf below 40 Hz.

Characteristics of Sound

Sound differ from each other in pitch, intensity, and quality.
Pitch refers to the highness and lowness of sound as one can hear them.
Frequency is the number of vibrations per second, pitch varies with frequency

  • Sound is produced when any object vibrates
  • Pitch is how low or high a sound seems
  • Sounds that are higher in frequency than humans can hear are called ultrasonic sounds.
  • Intensity is how loud or soft a sound is
  • Amplitude can make sounds louder by moving more air
  • Doppler effect are waves compressed in the direction of movement and lengthen it
  • Ultrasound are sound waves beyond the range of human hearing can only be heard with a machine.
  • Rarefaction is where molecules are spread out
  • Compression is where molecules are spread together
  • Sound measurement is measured by decibels
  • Concerning tones, the fundamental tone is the lowest frequency and the overtone are the other high-frequency tones

Detecting objects with Sound[edit | edit source]

  • Sonar: Sound Navigation and Ranging
  • Sound Waves are sent out and the reflected waves are analyzed.
  • Ultrasound: Similar to SONAR except the sound waves are beyond the range of human hearing.

Travel through Time by Riding the Sound. By Dr. Emad Kayyam
  • Electrostatic microphones: are frequently used for measurement since they are easily downsized, have flat frequency responses over a wide frequency range, and provide markedly high stability.

NIHL can also be caused by extremely loud bursts of sound, such as gunshots or explosions, which can rupture the eardrum or damage the bones in the middle ear. This kind of NIHL can be immediate and permanent. Loud noise exposure can also cause tinnitus—a ringing, buzzing, or roaring in the ears or head.

  • Damage the organ designed to detect it.
  • Sense of hearing can be damaged by exposure to very loud sounds
  • Depends on how near, how loud, how long, and how often the ear is subjected to the sound.

What is music, is it just noise or is it art? Not everyone enjoys the same music or the same noise but what this two things do have in common is that both are sound. Some think that noise is just an unpleasant sound while other might say that to them it is “music to their ears”. Due to the fact that today we have electronica devises we are able to put sound in almost anything. What is amazing is that the base of music is typically classified in three groups which are stringed, wind, and percussion instruments. These three groups are the traditional tools of music and there is no sign of them being replaced by any new technology.

Stringed Instruments: Basically it is when the vibration of strings are transferred to a sounding borad then into the air. Some examples of stringed instruments are violin, cello, guitar, harp, and even piano there are many more but this are the most common.

Woodwind Instruments: This are used more like when a stream of air is blown across a hole near one end of the instrument and the column of air inside the instrument vibrates. Some examples of woodwind instruments are piccolo, and flute. There is air blown into a mouthpiece which is called a reed then that reed vibrates which then make the column vibrate making in make a sound.

Percussion Instruments: Castanets, wood block, bells, and chimes are classified as percussion. Reason for that is when work is done by striking the surface to produce sound. These instruments are usually made out of solid material which would be wood and mental. This instruments vibrate when struck by hand or mallet or another object in this case.

Brass Instruments

Many of the world’s most important genres, including jazz and orchestral music, wouldn’t be possible without the use of brass instruments. Whether you’re new to the world of brass instruments or have some understanding, this helpful guide will explain the differences between the many different types of brass instruments.

Some of these brass instruments are the trumpet, cornet, buggle, French horn, tuba and trombone. All this instruments got their name because they are made of brass. The column of air inside the instrument is made to vibrate by pressing the lips against a metal mouthpiece and vibrating the lips while blowing into the mouthpiece. With most brass instruments, the enght of the air column is changed by pressing and releasing valves, which add or delete segments of tubing the air flows through. Some of this brass instruments have no valves to change the lenght of the vibrating air column.

Electronic Musical Instruments

Electronic musical instruments are very different from conventional musical instruments. They use electronics to produce vibrations in loudspeakers. Electronic instrument, any musical instrument that produces or modifies sounds by electric, and usually electronic, means. The electronic element in such music is determined by the composer, and the sounds themselves are made or changed electronically. Instruments such as the electric guitar that generate sound by acoustic or mechanical means but that amplify the sound electrically or electronically are also considered electronic instruments. Their construction and resulting sound, however, are usually relatively similar to those of their nonelectronic counterparts.


Anatomy, physiology and hygiene (1890) (14761262691)

All human beings have a “voice box” that is known as larynx which has two thin, strong bands of tissue stretched over it. We also have folds or as we commonly know them vocal cords. Men tend to have thicker vocal cords than women. Air passes through your vocal cords while you breathe. Furthermore, vocal cords have muscles attached to them which allow you to tighten them. When doing this, and force air past them, this causes the cords to vibrate like the way a rubber band vibrate in a stream of air, and sound is created.

A perfect example is when a person hums when you place a finger in you throat while humming you can feel the vibrations. Men usually have lower voices than women there is also a wide variety of higher, and lower voices. Sound quality of the voice is affected by many factors like air passages in the throat,mouth, and nose. The position and shape of lips, tongue, and teeth, and the shape and condition of sinus cavities which function as resonating chambers.

Classroom Experiments With Sound[edit | edit source]

There are many classroom experiments that can be done which involve sound. Here are some videos and activities teachers can use to help children learn more about sound and also educate them about sound experiments that seem interesting and fun to do in a class setting. It can also help students understand how sound is created.

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