1© Manhattan Press (H.K.) Ltd. Loudness, pitch and quality Intensity level and loudness Intensity...
-
date post
19-Dec-2015 -
Category
Documents
-
view
221 -
download
2
Transcript of 1© Manhattan Press (H.K.) Ltd. Loudness, pitch and quality Intensity level and loudness Intensity...
© Manhattan Press (H.K.) Ltd. 1
• Loudness, pitch and qualityLoudness, pitch and quality
• • Intensity level and loudnessIntensity level and loudness
11.2 Properties of 11.2 Properties of soundsound
© Manhattan Press (H.K.) Ltd. 2
11.2 Properties of sound (SB p. 172)
Loudness, pitch and quality
sound human ear responded: 20 Hz – 20 000 Hzultrasonics: above this rangeinfrasonics: below this range (sources: earthquakes, thunder, volcanoes, heavy vibrating machinery)
Go to
More to Know 3More to Know 3Go to
More to Know 4More to Know 4
© Manhattan Press (H.K.) Ltd. 3
11.2 Properties of sound (SB p. 173)
Loudness, pitch and quality
(a) Loudness:- subjective sensation- determined by intensity of sound, sensitivity of ear
2
2Intensity
ra
a – amplitude of soundr – distance from source
(b) Pitch:- higher frequency, higher pitch
© Manhattan Press (H.K.) Ltd. 4
11.2 Properties of sound (SB p. 173)
Loudness, pitch and quality
(c) Quality:- depends on waveform of sound
Audio-frequency generator
Piano Guitar
© Manhattan Press (H.K.) Ltd. 5
11.2 Properties of sound (SB p. 174)
Intensity level and loudness
1. Intensity in decibels
dB 10
log 10
bel 10
loglevelIntensity
12
12
I
I
10-12 W m-2: threshold of
hearing for sound of 1 000 Hz
I: sound intensity
Unit: dB
Note: Intensity level increase of 3 dB corresponds to about doubling the sound intensity.
dB log 10 levelintensity Relative1
2
II Go to
More to Know 5More to Know 5
© Manhattan Press (H.K.) Ltd. 6
11.2 Properties of sound (SB p. 175)
Intensity level and loudness
1. Intensity in decibels
Intensity W m-2 dB
Threshold of pain 106 120
Thunder 105 110
Jet engine 104 100
Vacuum cleaner 1 60
Conversation 10-2 40
Rusting leaves 10-4 20
Threshold of hearing at 1 000 Hz
10-6 0
© Manhattan Press (H.K.) Ltd. 7
11.2 Properties of sound (SB p. 175)
Intensity level and loudness
1. Intensity in decibels
Threshold of hearing- minimum intensity of sound that normal human ear can hear
Threshold of pain- sound of intensity 1 W m-2 or higher which causes pain to our ears
Go to
Common Error
© Manhattan Press (H.K.) Ltd. 8
11.2 Properties of sound (SB p. 175)
Intensity level and loudness
2. Loudness of sound
- Human ear responds to sound over 120 dB- Ear is not equally sensitive to all frequencies
Go to
Example 2Example 2
Go to
Example 3Example 3
© Manhattan Press (H.K.) Ltd. 10
Ultrasonics in nature
Although ultrasonics is out of the audible range of human beings, it can be heard by some animals. For example, bats and dolphins use ultrasonics of frequencies 20 kHz and 150 kHz respectively for communicating.
Return to
TextText
11.2 Properties of sound (SB p. 172)
© Manhattan Press (H.K.) Ltd. 11
Infrasonics in nature
Some animals such as elephants, rhinos and whales can hear infrasonics. It is believed that this ability helps them to have an early signal about earthquake and other weather disturbances. Return to
TextText
11.2 Properties of sound (SB p. 173)
© Manhattan Press (H.K.) Ltd. 12
Audible intensity range
Different people have different ranges of audible frequencies. The range usually decreases with age.
Return to
TextText
11.2 Properties of sound (SB p. 174)
© Manhattan Press (H.K.) Ltd. 13
11.2 Properties of sound (SB p. 175)
A sound of 0 dB does not mean that there is no sound anymore. It is the minimum sound that the human ears can detect and is equivalent to the threshold of hearing.
Return to
TextText
© Manhattan Press (H.K.) Ltd. 14
Q: Q: A small source of sound emits energy uniformly in all directions. For a particular frequency, the intensity of sound at a distance of 1.0 m from the source is 1.0 × 10−5 W m−2, and corresponds to an amplitude of oscillation of the air molecules of 70 m. Assuming sound is propagated without any loss of energy, find(a) the intensity of sound,(b) the amplitude of oscillation of the air molecules at a distance of 5.0 m from the source. Solution
11.2 Properties of sound (SB p. 176)
© Manhattan Press (H.K.) Ltd. 15
Solution:Solution:
m 14
7010011004
4 1004 3701001
)(Intensity (b)
m W 1004100105
01
05
01
101.0 :
21
2 5.0
1 m, 5.0 When
1011101.0 m, 1.0 When
1 )(Intensity (a)
25
72
27
25
2
2752
2
2
2
5
2
25
2
a..a
..................a.
...................aI
...
.I
.
.I
...............Ir
...............
rr
I
Return to
TextText
11.2 Properties of sound (SB p. 176)
© Manhattan Press (H.K.) Ltd. 16
Q: Q: A ship’s siren vibrates with displacement y where y = A sin200t(a) This sound causes the diaphragm of an eardrum of an observer 400 m away to vibrate. If the speed of sound is 340 m s−1, calculate
(i) the frequency of the sound,(ii) the number of wavelengths of this sound
between the siren and the eardrum,(iii) the phase difference between the vibrations
of the siren and the eardrum,(iv) the maximum energy of the eardrum if its
mass is 1.00 × 10−5 kg and the amplitude of its vibration is
1.00 × 10−8 m.(b) If the value of the speed and distance given were reliable only to 3 significant figures, comment on the confidence that could be placed in your answers to (a)(iii).
Solution
11.2 Properties of sound (SB p. 177)
© Manhattan Press (H.K.) Ltd. 17
Solution:Solution:
11.2 Properties of sound (SB p. 177)
(a) (i) Comparing the equation y = A sin200t with the wave equation y = A sint = A sin2ft
2ft = 200t Frequency (∴ f ) = 100 Hz
(b) If the value of the speed and distance were reliable to 3 significant figures, then the answer to (a)(ii) would be 118 and the phase difference in (a)(iii) would be zero.
J 100210001100210001212
21
21
eardrum ofenergy maximum efore ther motion, harmonic simplein vibratingis eardrum The (iv)
rad 1.220.6 eardrum theandsiren theof s vibrationebetween th difference Phase (iii)
61173.4400eardrum theandsiren ebetween th hs wavelengtofNumber
m 43100340h Wavelengt(ii)
168252222
...afmam
.
.fv
Return to
TextText