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Flashcards in Acoustics Deck (25)
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1

Sound

An auditory disturbance in a medium caused by a vibrating source

The disturbance must be capable of causing vibrations in a receiver

The receiver can be the auditory system

2

Prerequisites for Sound Production

A source of energy (lungs)

A vibrating source that will generate an audible pressure wave (vocal folds)

A medium of transmission (air)

3

Hearing Loss Levels

Normal Hearing Levels = -10 dB and 25 dB
Mild Hearing Loss = 26dB to 40 dB
Moderate Hearing Loss = 41 dB to 55 dB
Moderately-Severe Hearing Loss = 56 dB – 70 dB
Severe Hearing Loss = 71 dB – 90 dB
Profound Hearing Loss = 91 and greater

4

Hearing Loss and Language

Hearing loss > 60 dB limits perception of sound – child generally not able to produce normal oral language without intervention

Issues with pitch, loudness and resonance common in persons with HL > 60dB

> 90 dB – profoundly deaf and will not develop speech and language skills without educational and therapeutic intervention

5

The Role of Hearing in Language Development

Hearing is the most efficient way to develop spoken communication and literacy.

When we talk about hearing we talk about auditory brain development.

Technology is really a brain-access tool.

Stimulation of the auditory brain will permit it to develop. If the auditory brain is not stimulated, that area will be taken over by other skills, primarily visual.

Children need to hear 46 million words by age 4.

20,000 hours of listening is the basis for reading.

Children with hearing loss need three times the exposure to learn new words and concepts.

6

Simple Harmonic Motion

Pure tones

Periodic vibratory movement in which the vibratory body moves directly from one point of maximum displacement to the other point of maximum displacement

The forces of elasticity and inertia are simultaneously at work; As elasticity increases/inertia decreases and vice versa

Produces a sine wave – graph of simple harmonic motion

7

Inertia

Tendency for motion or lack of motion to continue

8

Elasticity

the restoring force that causes an elastic medium to bounce back when stretched or displaced

9

Periodic Tone

Sound waves in which the pattern of vibration, however complex, repeats itself exactly over time

Simple – One component frequency – a pure tone
Complex – Two or more component frequencies that are harmonically related: a fundamental frequency plus harmonics – A complex tone

10

Velocity

speed in a certain direction

Light travels faster than sound

A faint sound travels as fast as a loud one as long as temperature remains the same

Sound travels faster on a hot day vs. a cold day

11

Maximum velocity

reached each time the swing seat passes over its original resting place

12

Damping

decrease in the amplitude of displacement over time

the decrease in motion after force has been removed which will return the movement to the rest point

13

Complex Tone

Sound having more than one sine wave component

Periodic
Aperiodic

14

Aperiodic Tone

Sound wave in which the vibration is random and displays no repeatable pattern

Simple – Does not exist
Complex – Two or more component frequencies not harmonically related: no fundamental frequency, no harmonics - NOISE

15

Harmonic

An oscillation whose frequency is an integral multiple of the fundamental frequency

Example – violin
String is 100 Hz
Each half vibrates at 200 Hz
Each third at 300 Hz
And so on

Each tone generated by the complex vibration is called a harmonic

16

Waveform

a graphic representation of a vibratory event showing amplitude versus time

17

Frequency

is the number of vibratory cycles per second – measured in Hertz (Hz)

Healthy human listeners can detect vibrations as low as 20 Hz and as high as 20,000 Hz

Subsonic - Vibrations too low to be heard
Ultrasonic – vibrations too high to be heard

Frequencies most important for detection of the speech signal – 100 – 5000 Hz

18

Frequency

Number of completed vibratory cycles per second

Expressed in Hertz (Hz)

Period – time taken to complete each cycle

Healthy human listeners can detect vibrations as low as 20 Hz and as high as 20,000 Hz

Subsonic - Vibrations too low to be heard
Ultrasonic – vibrations too high to be heard

Frequencies most important for detection of the speech signal – 100 – 5000 Hz

19

Frequency

Number of completed cycles per second

Expressed in Hertz (Hz)

Period – time taken to complete each cycle

20

Wavelength

The length of a sound wave is the distance in space that one cycle occupies

21

Wavelength

The length of a sound wave is the distance in space that one cycle occupies

depends on the frequency of the vibration and the velocity of sound wave propagation in the medium (high frequency sounds occupy less space than low frequency sounds)

The medium through which sound travels – solids, liquids, gases

22

Resonance

Vibratory response to an applied force

23

Resonator

Something that is set into vibration by the action of another vibration

Does not initiate sound

Vibrates in sympathy to sounds created externally to them

The larger the vocal tract/cavity, the lower the frequencies to which they will resonate

The smaller the vocal tract/cavity, the higher the frequencies to which they will resonate

24

Acoustic Resonators

contain air

A body of air will resonate in response to sound containing frequencies

Musical instrument
Vocal tract
Ear canal

25

Clinical Applications of Acoustic Knowledge

Normal vocal fold vibration is periodic; aperiodicity may reflect vocal pathology

Acoustic analysis may reveal characteristics of speech that are not perceived auditorily

Audiology – uses pure tones to assess hearing acuity