Examination of changes in output diameter to improve producing Immersive Sound Field by air jet

One factor which influences the radiation of jet noise is the interaction with the heated moving flow of a parallel twin jet. Because of the temperature and flow discontinuity between the jet and the surrounding air, the parallel jet acts as a partial barrier between the noise source and the receiver. An analytical model of jet shielding has been developed consisting of the sound field emitted from a stationary, discrete frequency point source, which impinges on a cylinder of locally parallel flow. The model is analyzed to identify the zones in which the various shielding mechanisms dominate. The effects of such parameters as jet temperature and flow speed are investigated. The analytical model is compared to experimental results for the shielding of a point noise source adjacent to a subsonic, isothermal air jet. The model estimates the trends of sound amplification and reduction by the jet in downstream azimuthal planes, showing lobe formations similar to those found experimentally. The model underestimates the shielding in the shadow zone at far downstream locations where sound diffraction is the dominant mechanism. Resolution of this discrepancy by way of modification of the shielding jet model is discussed.

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On the Noise Emanating from a Two-Dimensional Jet Above the Critical Pressure

Aeronautical Quarterly ◽

10.1017/s0001925900000822 ◽

1953 ◽

Vol 4 (2) ◽

pp. 103-122 ◽

Cited By ~ 140

Author(s):

Alan Powell

Keyword(s):

Critical Pressure ◽

Elementary Theory ◽

Sound Field ◽

Acoustic Energy ◽

Small Scale ◽

Two Dimensional ◽

Symmetric Pattern ◽

Air Jet ◽

Simplifying Assumptions ◽

Radiated Sound

SummarySchlieren photographs of a small scale approximately two-dimensional air jet in air above the critical pressure have shown the existence of an instability displaying an anti-symmetric pattern, and the associated sound field having several distinguishing characteristics, has been photographed. An elementary theory based upon the hypothesis that the acoustic energy originates from the interaction of the stream disturbances with the shock waves of the flow, and connecting the stream disturbances with the radiated sound, is suggested. This is shown to be consistent with the physical dimensions of the phenomenon and predicts a sound field in reasonable agreement with that observed after certain simplifying assumptions have been made.

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Decay of Temporary Threshold Shift in Noise

Journal of Speech and Hearing Research ◽

10.1044/jshr.1602.267 ◽

1973 ◽

Vol 16 (2) ◽

pp. 267-270 ◽

Cited By ~ 5

Author(s):

John H. Mills ◽

Seija A. Talo ◽

Gloria S. Gordon

Keyword(s):

Sound Field ◽

Threshold Shift ◽

Temporary Threshold Shift ◽

Octave Band ◽

Band Noise ◽

Lower Asymptote

Groups of monaural chinchillas trained in behavioral audiometry were exposed in a diffuse sound field to an octave-band noise centered at 4.0 k Hz. The growth of temporary threshold shift (TTS) at 5.7 k Hz from zero to an asymptote (TTS ∞ ) required about 24 hours, and the growth of TTS at 5.7 k Hz from an asymptote to a higher asymptote, about 12–24 hours. TTS ∞ can be described by the equation TTS ∞ = 1.6(SPL-A) where A = 47. These results are consistent with those previously reported in this journal by Carder and Miller and Mills and Talo. Whereas the decay of TTS ∞ to zero required about three days, the decay of TTS ∞ to a lower TTS ∞ required about three to seven days. The decay of TTS ∞ in noise, therefore, appears to require slightly more time than the decay of TTS ∞ in the quiet. However, for a given level of noise, the magnitude of TTS ∞ is the same regardless of whether the TTS asymptote is approached from zero, from a lower asymptote, or from a higher asymptote.

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Modified Earpieces and CROS for High Frequency Hearing Losses

Journal of Speech and Hearing Research ◽

10.1044/jshr.1101.204 ◽

1968 ◽

Vol 11 (1) ◽

pp. 204-218 ◽

Cited By ~ 9

Author(s):

Elizabeth Dodds ◽

Earl Harford

Keyword(s):

Hearing Loss ◽

Hearing Aids ◽

High Frequency ◽

Hearing Aid ◽

Sound Field ◽

Intensity Level ◽

Test Results ◽

High Frequency Hearing Loss ◽

Increased Sensitivity ◽

Difficult Cases

Persons with a high frequency hearing loss are difficult cases for whom to find suitable amplification. We have experienced some success with this problem in our Hearing Clinics using a specially designed earmold with a hearing aid. Thirty-five cases with high frequency hearing losses were selected from our clinical files for analysis of test results using standard, vented, and open earpieces. A statistical analysis of test results revealed that PB scores in sound field, using an average conversational intensity level (70 dB SPL), were enhanced when utilizing any one of the three earmolds. This result was due undoubtedly to increased sensitivity provided by the hearing aid. Only the open earmold used with a CROS hearing aid resulted in a significant improvement in discrimination when compared with the group’s unaided PB score under earphones or when comparing inter-earmold scores. These findings suggest that the inclusion of the open earmold with a CROS aid in the audiologist’s armamentarium should increase his flexibility in selecting hearing aids for persons with a high frequency hearing loss.

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