acoustics 1 - sound as energy

8/20/2019 Acoustics 1 - Sound as Energy

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Acoustics acoustics n. 1. (used with a sing. verb)

The scientific study of sound, especially of its generation, transmission, and reception.


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The Physics of Sound

Soundwaves in air (compression/rarefaction)

Frequency and Amplitude

Speed of sound

Wavelength

Reverberation and Echo


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What is Sound?


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Plop

Sound is an energy that

travels periodically through a

medium. When a sound is

made the ripples it makes in

air are similar to the wavescreated when water is

disturbed, and so we use the

term sound wave. However…


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Sound moves away from a sound source (in this case, a piano) with

equal energy in every direction.

Sound energy is

OMNIDIRECTIONAL.


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A sound wave is a visual

representation of what

is really an outwardly

pulsating sound bubble.


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The COMPRESSION and RAREFACTION of air molecules.

Sound waves propagate through air. Air is a mixture of gases: oxygen and

nitrogen, which consists of atoms; and carbon dioxide, which is made up ofmolecules. When there is a disturbance of these particles (from a sound

source) a chain reaction is caused, whereby the atoms and molecules collide

through vibrations and oscillations.


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When Pitching Forks vibrate they

create regular periods of high and

low pressure. These are known as the

compressions and rarefactions of the air

molecules, and will produce a‘frequency’.


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Frequency

One compression with one rarefaction is called a

cycle. The number of these cycles (completed

compressions and rarefactions) that occur within

one second is called frequency. Frequencies are

measured in Hertz.


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Our frequency spectrum (the perfect human hearing range from the

lowest pitch to the highest) is 20 Hertz (Hz) to 20,000 Hertz (20KHz).

This range diminishes over time.


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Musical notes are set to

specific frequencies. Concert

pitch A being 440 Hz. An Anote played an octave higher

is 880 Hz.


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Speed of Sound


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Each frequency has its own WAVELENGTH. High frequencies are more easily

absorbed than low frequencies.


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= wavelength

f = frequency v = velocity (speed of

sound)

V (344m/s)

f


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344 Hertz

344 metres0 metres distance

What is the wavelength of 344Hz?

0 seconds time 1 second


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688 Hertz

344 metres0 metres distance

What is the wavelength of 688 Hz?

0 seconds time 1 second


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The Ear

acoustics 1 - sound as energy

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