SOUND WAVES

SOUND WAVES

Sound can propagate through a medium such as air, water and solids as longitudinal waves and also as a transverse wave in solids (see Longitudinal and transverse waves, below). The sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium. As the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure, velocity, and displacement of the medium vary in time. At an instant in time, the pressure, velocity, and displacement vary in space. Note that the particles of the medium do not travel with the sound wave. This is intuitively obvious for a solid, and the same is true for liquids and gases (that is, the vibrations of particles in the gas or liquid transport the vibrations, while the average position of the particles over time does not change). During propagation, waves can be reflected, refracted, or attenuated by the medium.

The behavior of sound propagation is generally affected by three things:

*A complex relationship between the density and pressure of the medium. This relationship, affected by temperature, determines the speed of sound within the medium.

*Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction. If the sound and wind are moving in opposite directions, the speed of the sound wave will be decreased by the speed of the wind.

*The viscosity of the medium. Medium viscosity determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

When sound is moving through a medium that does not have constant physical properties, it may be refracted (either dispersed or focused).

Spherical compression (longitudinal) wavesThe mechanical vibrations that can be interpreted as sound can travel through all forms of matter: gases, liquids, solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through a vacuum.

SOUND AND IT’S MEDIUM

Sound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. ... Sound travels about four times faster and farther in water than it does in air.

FACTORS AFFECTING THE SPEED OF SOUND

Air density affects it. Temperature, pressure, humidity and gas mixture can each affect the density. In liquid: The speed of sound is affected by density and viscosity. These in turn are affected by temperature, pressure, composition and currents (as with wind).

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CHARACTERISTICS AND PROPERTIES OF SOUND

Six Basic Properties of Sound

*Frequency/Pitch.

*Amplitude/Loudness.

*Spectrum/Timbre.

*Duration.

*Envelope.

*Location.

A sound can be characterized by the following three quantities: (i) Pitch. Pitch is the frequency of a sound as perceived by human ear. A high frequency gives rise to a high pitch note and a low frequency produces a low pitch note.

Sound waves are often simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties:

*Frequency, or its inverse, wavelength.

*Amplitude, sound pressure or Intensity.

*Speed of sound.

*Direction.

PARTS AND FUNCTION OF HUMAN EAR

Pinna: The pinna is the outer, visible part of the human ear. Its curves and folds are specially designed to gather sound from the environment and funnel it into our ears. People with pinnas that have been damaged can still hear, but typically do not hear as well as people with intact pinnas.

Ear Canal   : The ear canal is the opening through which sound waves enter the middle ear. It serves to further focus and concentrate the vibrations collected by the pinna, ensuring that the vibrations will be clear and strong enough to be amplified and turned into nerve impulses.

The ear canal is only 2-3 centimeters deep – a little bit less than one inch. About an inch inside ear canal, the tympanic membrane, or the “eardrum” is found.

This is why it’s important not to stick anything into your ears; damage to the delicate tympanic membrane can result in impaired hearing!

Tympanic Membrane: The tympanic membrane, or “ear drum” is a thin, tightly-stretched membrane that separates the outer from the middle ear. Just like the membrane of an actual drum, the tympanic membrane vibrates in response to the sounds that are funneled to it by the pinna and ear canal.

The outside of the tympanic membrane faces the ear canal. Its inner surface faces the malleus, incus, and stapes, which act to further focus and amplify the vibrations that the tympanic membrane receives.

Ossicles: The malleus, incus, and stapes are three tiny, remarkable bones. As a group they are sometimes called “ossicles,” from the root word “osseo” for “bone.” The ossicles are are labeled in the diagram below:

They are precisely shaped to vibrate in response to the movements of the tympanic membrane – and to transmit and focus those vibrations so that they become even clearer.

These bones contact the eardrum, or tympanic membrane, on the outside of the middle ear. They then transmit its vibrations through their specially-shaped bone structures and ultimately into the oval window.

Oval Window: The oval window is a small membrane which lies at the border between the middle and inner ears. Just as the tympanic membrane receives vibrations from the ear canal, the oval window receives vibrations from the malleus, incus, and stapes.

Cochlea: The cochlea is filled with fluid, and “hair cells” that are extremely sensitive to vibration. The cochlea, and the auditory nerve which carries signals from the cochlea to the brain

Semicircular Canals: The semicircular canals are similar to the cochlea in that they are bony canals which are filled with fluid and lined with hair cells. However, the hair cells in the semicircular canals are used for a different purpose from those in the cochlea. Instead of being turned into the sensation of sound, the signals from these hair cells are turned into information about movement and balance.