Page 91 - The Master Handbook Of Acoustics
P. 91
66 CHAPTER THREE
20
Related-sound pressure level - dB 5 5 0
15
10
10
15
0.1 0.2 0.5 1 2 5 10 20
Frequency - kHz
FIGURE 3-15
A measured example of the sound pressure (transfer function) at the opening of the ear
canal corresponding to sound arriving from a point immediately in front of the subject.
The shapes of such transfer functions vary with the horizontal and vertical angles at
2
which the sound arrives at the pinna. (After Mehrgardt and Mellert. )
20
Related-sound pressure level - dB 5
15
10
5
0
10
0.2
0.1
2
1
0.5
Frequency - kHz 5 10 20
FIGURE 3-16
The transfer function of Fig. 3-15 at the opening of the ear canal is altered to this shape
at the eardrum after being combined with the transfer function of the ear canal. In
other words, a sound arriving at the opening of the ear canal from a source directly in
front of the observer (Fig. 3-15) looks like Fig. 3-16 at the eardrum because it has been
combined with the characteristics of the ear canal itself (Fig. 3-3). The brain has no
trouble subtracting the fixed influence of the ear canal from every changing arriving
sound.
