Phys 1240: Sound and Music
LAST: decibels
TODAY: decibels and hearing
NEXT: sound and hearing
READ: 6.6 (mostly, try to make
sense of Fig 6.12!)
CAPA 5 due tonight.
Exam 2 is next Thursday.
5.2.3b
There are two instruments, a trumpet and
a flute. The trumpet produces a sound
with100x more intensity than that of the
flute.
The SIL (decibel level) for the trumpet
is…compared to the flute.
a) 2 dB greater
b) 10 dB greater
c) 20 dB greater
d) 100 dB greater
e) Other/Not enough information/???
Decibels as "relative SIL’s"
Difference in
SIL
0 dB
Ratio of
intensities
1
10 dB
10
20 dB
100
30 dB
1,000
50 dB
100,000
=105
100 dB
1010
5.2.5
If a sound is 0 dB, is any energy
transferred?
a) Yes
b) No
c) ??
Diff in SIL
Intensity ratio
0 dB
1
1 dB
2 dB
3 dB
…
10 dB
…
10
(etc - see Table 5.1 in text)
Diff in SIL
Intensity ratio
0 dB
1
1 dB
1.26 (call it 1.3)
2 dB
1.6
3 dB
2
…
10 dB
…
10
(etc - see Table 5.1 in text)
5.2.4b
A trumpet produces a sound 2x more
intense than the flute.
Compared to the SIL (“decibel level”) of
the flute, the decibel level of the trumpet
is…
A) 1.6 dB louder
B) 2 dB louder
C) 3 dB louder
D) 20 dB louder
E) You can’t answer unless I tell you
how many dB the flute is!
5.2.4bii
A flute plays at 60 dB.
A trumpet produces a sound 2x more
intense than the flute.
The decibel level of the trumpet is…
A) 120 dB
B) 2 dB
C) 80 dB
D) 62 dB
E) 63 dB
5.2.4b
A trumpet is 20x more intense than a
flute.
How many decibels louder is the
trumpet?
A) 3 dB higher
B) 12 dB higher
C) 13 dB higher
D) 20 dB higher
E) 23 dB higher
5.2.4c
A trumpet is 22 dB more than the flute.
The ratio of intensities,
I(trumpet)/I(flute), is…
A)
B)
C)
D)
E)
16
22
about 30
160
200
5.2.4d
A violin is playing at 55 dB. If you add a
second violin, what happens to the SIL?
A) Stays the same, still 55 dB
B) Goes to 57 dB
C) Goes to 58 dB
D) Goes to 75 dB
E) Goes to 110 dB
5.2.4e
A violin is playing at 60 dB. What
happens to the SIL if there are 20
violins playing?
A) Goes to 73 dB
B) Goes to 76 dB
C) Goes to 80 dB
D) Goes to 120 dB
E) Goes to much more than 120 dB