Sound

Chapter 2

Parameters:

describe the features of a sound wave

How many parameters are there?

7

What are the 7 parameters?

period, frequency, amplitude, power, intensity, wavelength, & propagation speed

Period:

time it takes a wave to vibrate a single cycle

What unit is used to report a period?

seconds

Is a period adjustable?

No

Frequency:

the number of cycles that occur in one second

What unit is used to report frequency?

Hz

Is frequency adjustable?

No

Infrasonic or Infrasound:

below the threshold of human hearing (<20 Hz)

Ultrasonic or Ultrasound:

above the threshold of human hearing (>20,000 Hz)

What does frequency affect?

penetration & image quality

What is the relationship between frequency & period?

inversely related

As frequency increases…

period decreases

As frequency decreases…

period increases

Inversely related:

when one variable increases, the other variable decreases

What is required for sound to travel?

a medium

Compressed:

squeezed together

Rarefied:

stretched apart

Sound travels…

in a straight line

Acoustic variables:

are recordable changes occurring in the medium because of sound traveling through the medium

What are the 3 variables used to distinguish between sound waves & other types of waves?

pressure, density, & distance

A sound wave is also known as…

an acoustic wave

Pressure is measured in…

pascals (Pa)

Density is measured in…

kg/cm³ (kilograms per cubic centimeter)

Distance is measured in…

cm & mm

What are acoustic propagation properties?

the effects of the medium upon the sound wave

What are biologic effects?

effects of the sound wave upon the biologic tissue through which it passes

Transverse waves:

particles move in a direction perpendicular (at 90°) to the direction that the wave propagates

Longitudinal waves:

particles move in the same direction that the wave propagates; ex: sound

In-phase waves:

peaks (maximum values) occur at the same time & at the same location

troughs (minimum values) occur at the same time

Out-of-phase waves:

peaks & troughs occur at different times

Interference…

will affect both in & out of phase waves, but combine differently

Examples of interference:

more than one sound beam can travel through a medium

multiple beams may arrive at an identical location at exactly the same time

waves lose their individual characteristics and combine to form a single wave

Name the 2 types of interference:

constructive & deconstructive

Constructive interference:

interference of a pair of IN-phase waves that results in the formation of a single wave of greater amplitude than either of its components

Destructive interference:

interference of a pair of OUT-of-phase waves that results in the formation of a single wave of lesser amplitude than either of its components

What happens when 2 OUT-of-phase waves are of equal amplitude?

complete destructive interference occurs; meaning they will cancel each other out

What happens in the interference of waves with different frequencies?

both constructive & destructive interference may occur because sometimes the waves are in-phase, other times they are out-of-phase

What determines the speed of sound?

the medium

Sound is a form of what energy?

mechanical

What is the speed of sound through tissue?

1540 m/s (meters per second)

Sound cannot travel through a…

vacuum