10. Acoustic Models of Sound Production
441
two peculiarities of the model may have contributed to lowering the computed directivity indexes. First, the incomplete air sac model may have
lowered the computed indexes at all frequencies. Second, because point
sources emit uniformly in all directions, one expects the use of point sources
in these simulations to have lowered the computed directivity indexes by
amounts that depend on the frequency and assumed geometry of the signal
generator. For these reasons, the demonstrated focal characteristics of the
forehead tissues are expected to be conservative.
The forehead tissue structures of the common dolphin are representative
of members of the odontocete family Delphinidae having an intermediateto-moderate value of soft tissue asymmetry (Cranford 1992). It is expected
that similar if not identical mechanisms operate in all delphinids exhibiting
intermediate-to-moderate soft tissue asymmetry (including T. truncatus). It
is also reasonable to suggest that similar mechanisms may operate in all
odontocetes that possess forehead tissue morphologies resembling those of
the common dolphin.
The techniques utilized here to investigate the biosonar system of D.
delphis are applicable to many other marine mammal species. Investigation
of odontocete species with better studied biosonar emission fields (i.e., T.
truncatus, Delphinapterus leucus, Pseudorca crasidens) would serve to test
the generality of the emission mechanisms discussed above. In addition to
sound emission, the same techniques may be used to model hearing. Aroyan
(1996) simulated individual right and left ear receptivity patterns and tissue
reception pathways in the common dolphin using techniques that are widely
applicable to other marine mammals. Extensions of the method for modeling the acoustical parameters of biological tissues from X-ray cr data
presented in Section 2.2 may enable a host of bioacoustic applications.
Finally, the power of combined propagation and extrapolation techniques
has yet to be exploited in several areas of physical acoustics.
5. On the Physics of Sound Production in the
Blue Whale
Blue whales (B. musculus) produce loud low-frequency underwater sounds,
providing a practical tool to study whale distribution and movements
(Thompson and Friedl 1982; McDonald et al. 1995; Stafford 1995). The
blue whale is not only the largest animal alive, but is also the loudest,
making it an excellent choice for sound production mechanism study. Previous publications on the physics of the baleen whale sound production
mechanism have concentrated on bubble resonance (Harris 1964; Barham
1973), a phenomena where a given air volume at a given depth will resonate
to produce sound efficiently at an acoustic frequency that can be calculated.
We propose that a Helmholtz resonance better fits the observations in
that, unlike bubble resonance, Helmholtz resonance provides efficient
441
two peculiarities of the model may have contributed to lowering the computed directivity indexes. First, the incomplete air sac model may have
lowered the computed indexes at all frequencies. Second, because point
sources emit uniformly in all directions, one expects the use of point sources
in these simulations to have lowered the computed directivity indexes by
amounts that depend on the frequency and assumed geometry of the signal
generator. For these reasons, the demonstrated focal characteristics of the
forehead tissues are expected to be conservative.
The forehead tissue structures of the common dolphin are representative
of members of the odontocete family Delphinidae having an intermediateto-moderate value of soft tissue asymmetry (Cranford 1992). It is expected
that similar if not identical mechanisms operate in all delphinids exhibiting
intermediate-to-moderate soft tissue asymmetry (including T. truncatus). It
is also reasonable to suggest that similar mechanisms may operate in all
odontocetes that possess forehead tissue morphologies resembling those of
the common dolphin.
The techniques utilized here to investigate the biosonar system of D.
delphis are applicable to many other marine mammal species. Investigation
of odontocete species with better studied biosonar emission fields (i.e., T.
truncatus, Delphinapterus leucus, Pseudorca crasidens) would serve to test
the generality of the emission mechanisms discussed above. In addition to
sound emission, the same techniques may be used to model hearing. Aroyan
(1996) simulated individual right and left ear receptivity patterns and tissue
reception pathways in the common dolphin using techniques that are widely
applicable to other marine mammals. Extensions of the method for modeling the acoustical parameters of biological tissues from X-ray cr data
presented in Section 2.2 may enable a host of bioacoustic applications.
Finally, the power of combined propagation and extrapolation techniques
has yet to be exploited in several areas of physical acoustics.
5. On the Physics of Sound Production in the
Blue Whale
Blue whales (B. musculus) produce loud low-frequency underwater sounds,
providing a practical tool to study whale distribution and movements
(Thompson and Friedl 1982; McDonald et al. 1995; Stafford 1995). The
blue whale is not only the largest animal alive, but is also the loudest,
making it an excellent choice for sound production mechanism study. Previous publications on the physics of the baleen whale sound production
mechanism have concentrated on bubble resonance (Harris 1964; Barham
1973), a phenomena where a given air volume at a given depth will resonate
to produce sound efficiently at an acoustic frequency that can be calculated.
We propose that a Helmholtz resonance better fits the observations in
that, unlike bubble resonance, Helmholtz resonance provides efficient