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Sound pressure distribution and power flow within the gerbil ear canal from
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10.1121/1.2769625
/content/asa/journal/jasa/122/4/10.1121/1.2769625
http://aip.metastore.ingenta.com/content/asa/journal/jasa/122/4/10.1121/1.2769625
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Theoretical standing waves in a uniform cylindrical tube. (A) Spatial variations in sound pressure magnitude (top) and phase (bottom) at a given frequency for different values of , the ratio of the amplitude of a sound wave reflected from the termination to the incident sound wave amplitude. (B) Computed broadband sound pressure spectra at different locations for . If changes slowly with frequency, the spectra are equivalent to the spatial sound pressure distribution—see lower horizontal scale in wave number .

Image of FIG. 2.
FIG. 2.

Schematic section through a gerbil head showing preparation methods and measurement trajectories. (A) Coronal section. The external ear and soft tissue were removed, the lateral wall of the bony ear canal (EC) opening was trimmed back, and a brass tube sound coupler was placed at the opening of the bony ear canal. A reflector was placed on the stapes posterior crus, and the laser vibrometer beam was shined through one or more holes in the middle ear wall toward the reflector. (B) Details of the coronal EC section showing EC sound pressure measurement trajectories. The microphone probe tube (MEEI) or fiber-optic microphone (Princeton and Columbia) was introduced through a notch in the coupler wall and advanced in steps toward the umbo “” along an approximately longitudinal trajectory “L.” was also measured with the fiber-optic microphone along an medio-axial trajectory through the middle-ear wall “MA” toward the umbo. (C) Section perpendicular to the coronal section in panel (B). was also measured along a transverse trajectory across the ear canal over the umbo approximately from the tympanic ring.

Image of FIG. 3.
FIG. 3.

Section through the calibration coupler used (A) for microphone calibrations and (B) as an “artificial ear.” The sound delivery tube was i.d. Tygon with a long brass section that fit into the acrylic body of the calibration coupler ( diameter in front of the reference microphone). For the “artificial ear calibration,” the setup in (A) was used, the probe tube was replaced with a plug as in (B), and the brass tube was withdrawn about from the position shown.

Image of FIG. 4.
FIG. 4.

Sensitivity and frequency response of the probe-tube microphone (MEEI, solid curve) and miniature fiber optic microphone (Princeton and Columbia, dashed curve). Top: Magnitude; bottom: phase relative to sound pressure condensation.

Image of FIG. 14.
FIG. 14.

Ratio of sound pressure measured at the terminating microphone of the artificial ear to measured near the umbo in four gerbil ears. The length of the artificial ear was adjusted to mimic the length of the gerbil bony ear canal. Data are not shown below because leaks between the probe tube and the ear canal influence the results. Top: Magnitude; bottom: phase. The artificial ear calibration overestimates at low frequencies and underestimates between 40 and .

Image of FIG. 5.
FIG. 5.

Variations in ear canal sound pressure measured in steps along trajectory L [see Fig. 2(b)] in ear 0402R with the probe tube microphone (MEEI) in response to a chirp stimulus. Shown is , the ratio of in various locations along the trajectory to near the umbo. (A) at six locations, plotted on a logarithmic frequency scale. Variations in are small below . Top: Magnitude ratio in decibels; bottom: phase difference. (B) in the six locations, shown individually on a linear frequency scale. Left: Magnitude ratios in decibels; right: phase differences. Arrows indicate frequencies of notches and frequencies where crosses 0.25 or . (C) The curves from (B) superposed, plotted on a linear frequency scale. Top: Magnitude ratio in decibels; bottom: phase difference.

Image of FIG. 6.
FIG. 6.

Variations in ear canal sound pressure measured in steps along trajectory L [see Fig. 2(b)] in ear ESO3 just post-mortem with the miniature fiber optic microphone (Columbia) in response to a series of tones. Shown is at six locations, computed as in Fig. 5 and plotted on a linear frequency scale. Top: Magnitude ratio in decibels; bottom: phase difference. Variations in with position and frequency are similar to those in Fig. 5.

Image of FIG. 7.
FIG. 7.

near the opening of the bony ear canal in five ears measured at MEEI and Columbia. Top: Magnitude ratio in decibels; bottom: phase difference.

Image of FIG. 8.
FIG. 8.

Variations in ear canal sound pressure measured in steps along a medio-axial trajectory “MA” [see Fig. 2(b)] in ear ESO2 with the miniature fiber optic microphone (Princeton) in response to a series of tones. Shown is at five locations, computed as in Fig. 5 and plotted on a linear frequency scale. Top: Magnitude ratio in decibels; bottom: phase difference. Variations in with position and frequency resemble those in Figs. 5 and 6 at locations 1.5 and from the umbo.

Image of FIG. 9.
FIG. 9.

Variations in ear canal sound pressure measured in steps along an transverse trajectory from the tympanic ring [see Fig. 2(c)] in ear 0305L (just post-mortem) with the probe-tube microphone (MEEI) in response to a chirp stimulus. Shown is at three locations, computed as in Fig. 5 and plotted on a linear frequency scale. Variations in are small below . Top: Magnitude ratio in decibels; bottom: phase difference.

Image of FIG. 10.
FIG. 10.

Variations in sound pressure measured axially in steps within an artificial ear with the probe-tube microphone (at MEEI) in response to a chirp stimulus. The artificial ear was terminated with a condenser microphone. (A) , the ratio of at six locations to near the termination, shown individually on a linear frequency scale. Left: Magnitude ratios in decibels; right: phase differences. Arrows indicate frequencies of notches and frequencies where crosses 0.25 or . (B) The curves from (A) superposed, plotted on a linear frequency scale. Top: Magnitude ratio in decibels; bottom: phase difference.

Image of FIG. 11.
FIG. 11.

Standing wave patterns at frequencies of notches in sound pressure spectra, constructed from sound pressure spectra measured at various locations. Because the MEEI data were taken with a chirp (broadband) stimulus, the frequencies at which notch minimums occurred could be identified reliably. (A) Standing wave patterns in ear 0402R computed from at various EC locations, from Fig. 5(c). (B) Standing wave patterns in the artificial ear computed from at various locations, from Fig. 10(b). Top: Magnitude at frequencies of magnitude notches; bottom: Phase at frequencies of magnitude notches.

Image of FIG. 12.
FIG. 12.

Comparison of the frequencies of sound pressure magnitude notches at measurement locations to the theoretical -wave notch frequencies and locations in a rigidly terminated uniform tube (thick gray line). (A) In the artificial ear terminated by a reference microphone, spacing—closed symbols. (B) In five ear canals.

Image of FIG. 13.
FIG. 13.

Power reflectance computed from standing wave patterns in the artificial ear and in several gerbil ear canals. Shown are: in the artificial ear (thick solid line and closed symbols), computed from standing wave patterns of Fig. 11(b); in ear 0402R (thick solid line, open symbols), computed from standing wave patterns of Fig. 11(a); in other MEEI ears (thin dashed lines and open symbols), computed in a similar fashion; and computed from the mean middle-ear input impedance between and in 5 gerbil ears (gray line, from Ravicz et al., 1996).

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/content/asa/journal/jasa/122/4/10.1121/1.2769625
2007-10-01
2014-04-18
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Sound pressure distribution and power flow within the gerbil ear canal from 100Hzto80kHz
http://aip.metastore.ingenta.com/content/asa/journal/jasa/122/4/10.1121/1.2769625
10.1121/1.2769625
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