Audio Engineering

Measurement 71

For example, suppose that within the same critical band we have two tones each at 70
phons. Using Eq. (2-53),

PT 



10 10 10

73

(^70107010)
log()
phons.
An interesting experiment in this regard is to start with two equal level signals 10 Hz
apart at 1000 Hz and gradually separate them in frequency while maintaining their phon
level.
They will increase in apparent loudness as they separate. This is one of the reasons a
distorted system sounds louder than an undistorted system at equal power levels. One
fi nal factor worthy of storage in your own mental “ read-only memory ” is that in the 1000-
Hz region most listeners judge a change in level of 10 dB as twice or half the loudness of
the original tone.
Figure 2.18 is a chart of frequency and dynamic range for various musical instruments
and the upper and lower frequency range of the average young adult.
120
100
80
60
40
20
0
− (^10) 50 100 300 500 1k 3k 5k 10k 20k
Sound pressure level (dB)
Frequency (Hz)
Loudness
level (phons)
100
120
110
90
80
70
60
50
40
30
20
Maudinimumible 10
Figure 2.17 : Equal loudness contours.