sound. sound moves in 3 dimensions sound basics sound – a wave of energy created by vibrating...

Sound

Sound Moves in 3 Dimensions

Sound Basics• Sound – A wave of energy created by

vibrating objects that travels through a medium

• Origin – vibrating object– Ex. Vocal chords, strings and sound board of

cello, diaphragm of speaker

• “Sound” is heard when the human ear detects changes in air pressure

• Perception of sound is a matter of both physics and physiology

SOUND IS A MECHANICAL WAVE

• A Mechanical Wave: sound waves travel through air by way of particle interactions

• Mechanical waves require a medium through which to travel

• Cannot travel through a vacuum

• Sound is a longitudinal waveWatch one dot

Sound is a longitudinal wave which travels through the air through a series of compressions and rarefactions.

SOUND IS A PRESSURE WAVES

• Ex. A vibrating string– As the string vibrates outward, it displaces air, creating a high

pressure region– As the string vibrates in the opposite direction, it creates a low

pressure region• The particles of the sound wave collect in “compressions” (high

pressure areas) and “rarefactions” (low pressure areas)

Sound travels through different media.

We hear sound which usually travels through air. Sound travels through other media as well, such as water and various solids.

Sound travels different speeds in different media. Sound typically travels faster in a solid than a liquid and faster in a liquid than a gas.

The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound.

• Show FoP Sim

What is vibrating?

• Human voice?

• Drum?

• Trumpet?

• Violin?

• Motorcyle?

Human Hearing

• The human ear is incredibly sensitive.

• Can perceive sound that makes the eardrum vibrate only 1/10 the diameter of an atom. (10-11 m)

Perception of Sound

Sound Characteristic

Perception

Frequency Pitch

Intensity

(Amplitude2)

Loudness

(Volume)

Sound Intensity

• Waves transmit energy; sound waves transmit acoustic energy

• Intensity (I) is the measure of the how much energy passes through an area in a unit of time

• E

PtIA A

= = Units:

2

Wattsm

What determines if we hear a sound?

Frequency

human range is from 20 Hz to 20,000 Hz

Intensity (loudness)

human range is 1 x 10-12 W/m2

What are some ranges of hearing for other animals?

dogs – 50,000 Hz

bats – 100,000 Hz

Intensity Level in DecibelsSince the values of intensity are so small it is convenient to use a logarithmic scale of decibels

12o 2

10log where I 1 10o

I Wx

I m

Loudness• Loudness is not the same as Intensity of

sound. The Intensity of a sound that causes pain is 1013 times the Intensity of the softest sound that can be heard.

• We don’t perceive this range of intensity.

• The ear/nervous system responds to sound such that intensity must increase by 10 to sound twice as loud.

Perception of Sound

y= log10 (x) 10y = x

• First some log practice: Solve each of the following for the unknown variable.

• y = log (1000) _________ y = log (10-5) _________• y = log (0.005) _________ y = log (0.00001) _________• -3 = log (x) _________ 4.5 = log (x) _________• 4 = log (x/10-12) _________ 6 = log (x/10-12) _________• 5 = 10 log (x/10-12) _________ 8 = 10 log (x/10-12) _________• y = 10 log (10-4/10-12) _________• y = 10 log (2 x 10-5/10-12) _________

Decibel Level

1) more than 120 dB

2) 120 dB

3) between 60 dB and 120 dB

4) 60 dB

5) less than 60 dB

When Mary talks, she creates an intensity level of 60 dB at your location. Alice talks with the same volume, also giving 60 dB at your location. If both Mary and Alice talk simultaneously from the same spot, what would be the new intensity level that you hear?

Loudness in Decibels

How is frequency related to pitch?

The pitch of a sound wave is directly related to frequency. A high-pitched sound has a high frequency (a screaming girl). A low-pitched sound has a low frequency (a fog-horn).

A healthy human ear can hear frequencies in the range of 20 Hz to 20,000 Hz. Humans cannot hear below 20 Hz. Sounds below this frequency are termed infrasonic.

Sounds above 20,000 Hz are termed ultrasonic. Some animals, such as dogs, can hear frequencies in this range in which humans cannot hear.

Loudness (perception of intensity) depends on frequency (pitch)

How is frequency related to pitch?

The pitch of a sound wave is directly related to frequency. A high-pitched sound has a high frequency (a screaming girl). A low-pitched sound has a low frequency (a fog-horn).

A healthy human ear can hear frequencies in the range of 20 Hz to 20,000 Hz. Humans cannot hear below 20 Hz. Sounds below this frequency are termed infrasonic.

Sounds above 20,000 Hz are termed ultrasonic. Some animals, such as dogs, can hear frequencies in this range in which humans cannot hear.

Loudness (perception of intensity) depends on frequency (pitch)