10. Acoustic Models of Sound Production
449
rather than to produce the sound. It becomes obvious the whale's lungs
cannot provide the nearly 10 bar of pressure differential needed to provide
such a volume displacement while remaining near the surface. The whale
would be required to provide a slight differential pressure through muscular compression of its lungs in order to keep the laryngeal sac inflated preferentially during a dive and the whale would need to provide muscle control
over the oscillating valve. It seems possible the type "B" call is only produced during ascent, thus eliminating the need for the whale to provide positive differential pressure with its lungs as would be needed during descent.
If air were to escape from the system during sound production, such losses
would limit a whale's total call production between breathing periods,
making the observed call series impossible. It is generally believed that no
air escapes from baleen whales during sound production (Conner 1994,
p. 80), although whalers do report occasional "blow wakes," believed to
correspond to air expulsions, from submerged B. musculus while being
pursued with active sonar (Haines 1974).
The larger pliant membrane in Figure 10.17 will be completely collapsed
at a depth where the total air volume under pressure is just sufficient to fill
the smaller pliant and rigid volumes:
(7)
where Zc is the dive depth in m, P is the water pressure, and Po is pressure
at the surface, V L is the surface lung volume, p is the water density =
1,025kglm3, g is the acceleration due to gravity = 9.8m1s
2 , and V n is the
volume of the combined nasal passages and laryngeal sac.
As the system in Figure 10.22 is submerged, the volume flow rate of
air that passes the oscillating valve can be calculated as follows with m n
defined as
(8)
as the mass of air on the narial side (including laryngeal sac) of the oscillating valve corresponding to the arytenoid cartilages, V n is the volume of
air on the narial side, and Pn is the air density on the narial side. There must
be a fluctuating pressure in the laryngeal sac and nasal passages, but for the
purpose of calculating the change in the density of the air due to changes
in depth we assume the pressure on the narial side of the valve, is on
average, equal to the hydrostatic pressure in the seawater. The volume of
the air decreases with increasing pressure as the air is compressed during
descent. The density of air in the lungs increases linearly with depth as does
the pressure in the lung, PL:
Po = PL
Po p(z)
(9)
449
rather than to produce the sound. It becomes obvious the whale's lungs
cannot provide the nearly 10 bar of pressure differential needed to provide
such a volume displacement while remaining near the surface. The whale
would be required to provide a slight differential pressure through muscular compression of its lungs in order to keep the laryngeal sac inflated preferentially during a dive and the whale would need to provide muscle control
over the oscillating valve. It seems possible the type "B" call is only produced during ascent, thus eliminating the need for the whale to provide positive differential pressure with its lungs as would be needed during descent.
If air were to escape from the system during sound production, such losses
would limit a whale's total call production between breathing periods,
making the observed call series impossible. It is generally believed that no
air escapes from baleen whales during sound production (Conner 1994,
p. 80), although whalers do report occasional "blow wakes," believed to
correspond to air expulsions, from submerged B. musculus while being
pursued with active sonar (Haines 1974).
The larger pliant membrane in Figure 10.17 will be completely collapsed
at a depth where the total air volume under pressure is just sufficient to fill
the smaller pliant and rigid volumes:
(7)
where Zc is the dive depth in m, P is the water pressure, and Po is pressure
at the surface, V L is the surface lung volume, p is the water density =
1,025kglm3, g is the acceleration due to gravity = 9.8m1s
2 , and V n is the
volume of the combined nasal passages and laryngeal sac.
As the system in Figure 10.22 is submerged, the volume flow rate of
air that passes the oscillating valve can be calculated as follows with m n
defined as
(8)
as the mass of air on the narial side (including laryngeal sac) of the oscillating valve corresponding to the arytenoid cartilages, V n is the volume of
air on the narial side, and Pn is the air density on the narial side. There must
be a fluctuating pressure in the laryngeal sac and nasal passages, but for the
purpose of calculating the change in the density of the air due to changes
in depth we assume the pressure on the narial side of the valve, is on
average, equal to the hydrostatic pressure in the seawater. The volume of
the air decreases with increasing pressure as the air is compressed during
descent. The density of air in the lungs increases linearly with depth as does
the pressure in the lung, PL:
Po = PL
Po p(z)
(9)