Showing papers on "Sound intensity published in 1971"

Acoustical Detection of Single Cavitation Events in a Focused Field in Water at 1 MHz

Abstract: Acoustic intensities up to 1400 W/cm2 have been generated at the focus of a ceramic bowl. The rf voltage applied to the transducer has been rectified and filtered and the signals produced from cavitation events have been examined. A directional hydrophone simultaneously monitoring the focal point aided interpretation of the signals detected by the driven bowl. Low‐amplitude low‐frequency signals appeared on the driven bowl synchronously with the onset of first subharmonic emission in the water at an intensity of 13 W/cm2. The subharmonic increased rapidly with increasing sound intensity and then leveled off. Just before this occurred, the scattering properties of the focal region increased markedly and a cyclic signal, interpreted as indicating the production of clouds of microbubbles when surface oscillations set in on the cavitation bubbles, was detected on the filter circuit. Strongly radiating single cavitation events lasting for the order of milliseconds were also detected. The amplitude, duration, and rate of occurrence of these events were all one to two orders of magnitude greater in tap than in degassed water.

Effect of Temporal Summation on the Human Stapedius Reflex

Abstract: The sensitivity of the acoustic stapedius reflex as a function of stimulus duration was studied by monitoring acoustic-impedance changes at the eardrum. Our results indicate an unexpectedly pronounced duration effect. The sound intensity required for a criterion response had to be lowered by about 25 dB when the signal duration was increased from 10 to 100 msec.

Acoustically evoked potentials in midbrain auditory structures in sea lions (Pinnipedia)

Abstract: Twelve sea lions (Zalophus californianus) and one harbor seal (Phoca vitulina) were examined by recording evoked potentials in response to sound from the inferior colliculus and adjacent structures, under barbiturate or after implanting and coming out of anesthesia. Results were similar in air and under water. The averaged response evoked by a sharply rising tone consists of early, brief peaks and later, slow waves (Fig. 1). The latency of the earliest deflection is 3.5 to 4.8 ms from the moment of arrival of a sound pip at the ear. The potential increases in size with sound intensity approximately as a power function, over a dynamic range of 60–70 db (Fig. 2). Masking is qualitatively similar to that in common laboratory species. The properties of the midbrain response are strikingly different from those in porpoises, reported elsewhere. The pinniped is not so specialized for extremely short duration, fast rise time, sounds or for rapid recovery or ultrasonic frequencies (Figs. 3, 4, 7, 8). Evoked potentials fail to show response above 30–35 kHz at 100 db SPL; best frequency is about 4–6 kHz (Figs. 5, 6). Threshold by this method is about 20 db SPL in air. Frequency modulated tones are markedly more effective in some loci but less so than in porpoises under water. The receptive field is essentially total and directionality weak, in contrast with porpoises. Physiological results cannot settle the question whether echolocation is employed but they can indicate lack of high specialization for the types of sounds bats and porpoises use.

An input-output relation at the synapse between hair cells and eighth nerve fibers in goldfish

Abstract: Studies were made to clarify the nature of the coupling potentials which are produced, beside the EPSP's, in the eighth nerve fibers of goldfish in response to the sound stimulus. Analysis was made by studying semiquantitatively changes in the size of the coupling potentials, the EPSP's, and the microphonics upon changing the sound intensity; that is, an input-output relationship at the synapse between hair cells and eighth nerve fibers was studied. Results obtained are as follows:1. The coupling potentials were produced without any delay after the initiation of the microphonic deflections and their time course was similar to that of the latter. Also the amplitude of these two potentials was changed in parallel upon changing the intensity of the sound stimulus.2. EPSP's were produced with a definite delay after the initiation of the microphonics and their amplitude increased more steeply than the microphonics upon increasing the sound intensity. A 10dB increase in the sound intensity produced, in the exponential range, from 4- to 20-fold increase in the EPSP size.3. The coupling potentials, like the microphonics, showed a greater resistance to cooling and anoxia.4. It was concluded that the coupling potentials are quite different in nature from the EPSP's. While the EPSP's were generated in response to a released transmitter, the coupling potentials seem to have been produced in a more direct relationship with the microphonics.

Experimental Investigation for Detection of Sound-Pressure Level by a Microphone in an Airstream

Abstract: Investigations were made to find a physical concept for evaluating the pressure level of sound that exists in an airflow by means of a wind screen or probe microphone. In order to provide a sound pressure in the airflow, sound of a known pressure level, which is assumed to be of higher level than the aerodynamically generated noise, was radiated into a duct from an external sound source. The output level of the microphone was measured for various differences between the sound‐pressure level produced by the external sound source and the pressure fluctuation level of turbulence in the airflow. Results obtained agree with the superposed level of output by sound pressure and output produced by pressure fluctuation of turbulence. A new concept for characterizing microphone response to wind‐flow fluctuation is presented. This characteristic is defined by the difference between the magnitude of the pressure fluctuation of turbulence and the output level of the microphone produced by the turbulence‐fluctuated pre...

Reduction of gas turbine engine noise annoyance by modulation

Abstract: Method and apparatus for reducing the audible or annoying sound i.e., the noise emanating from a gas turbine engine are described. The sound energy is modulated by imposing on it a higher frequency sound source, which may be of either higher or lower intensity. In one form, the modulation is achieved by producing a higher frequency sound source with an ultrasonic siren. The higher frequency sound energy and the sound energy generated by the gas turbine engine interact so that the original tones disappear and two new tones appear, the new tones being at frequencies which occur at the sum and at the difference of the frequencies of the original tones.

Relation between the Normalized Impact Sound Level and Sound Transmission Loss

Abstract: An expression relating the normalized impact sound level (Ln) and the sound transmission loss (TL) of a floor is derived. It takes into account both the resonant and the forced response of the floor, thus extending the utility of the formulas derived previously by Heckl and Rathe into the frequency range below the critical frequency. This relation between normalized impact sound level and sound transmission loss permits an experimental evaluation of the potential TL of a floor partition in the presence of certain types of flanking.

Response contingent auditory reinforcement in the rat

Abstract: The acquisition and performance levels of responding for auditory intensity changes in rats are presented. A sound decrease was found to be more reinforcing than an equivalent sound increase. A preference experiment ruled out the possibility that the differences found could be accounted for by an aversion for the higher sound intensity. Several parallels between the reinforcing properties of sound and light intensity changes are drawn. The results are interpreted as showing that a change per se in the auditory modality can be reinforcing.

Detection of bubbles in tissues and blood

Abstract: Publisher Summary This chapter discusses the detection of bubbles in tissues and blood. An interface between a gas and either a liquid or a solid is a very good reflector of sound because of the great difference in acoustic impedance across the boundary. Pulsed ultrasonic energy has previously been used to image internal body structures using sonar-like systems. Most Doppler systems work at an unspecified sound intensity, often just under a level that would produce periosteal pain or burns. A sound wave applied to a bubble result in the production of some second harmonic, that is, some sound of twice the original frequency is returned along with that at the basic frequency. From long-term saturation dives, it may be possible to tell if altered blood flow patterns while asleep and awake during decompression demand periodically changed schedules.

Absorption of Finite-Amplitude Waves

Abstract: Normally in acoustics one is concerned with sound waves of small amplitude in the sense that the perturbations elicited by these waves in the equilibrium state of the medium are small. The propagation of such waves is described in terms of approximate equations derived by linearization of the hydrodynamic equations and equation of state. This, the so-called linear-acoustical approximation, proves inadequate for the case of sound waves of large intensity, which are being encountered on a growing scale in present-day engineering.

Sound Pressure in Water from Source in Air

Abstract: Sound pressure in the water under a point source overhead in air is shown by theory and experiment to propagate as from a virtual source situated (c1/c2) times the actual source height above the water and emitting unit‐distance sound pressure that is (2c1/c2) times the actual unit‐distance sound pressure, where c1 and c2 are the speeds of sound in air and water, respectively.

The Effect of Rotating Vanes on the Sound Field in Reverberation Chambers at Single Frequencies

Abstract: Results of the experimental investigation of the effect of rotating vanes on the sound field in reverberation chambers are presented. When the sound field is excited at single frequencies, the rotating vane splits the single‐line spectrum into a multiple‐line spectrum with the amplitude of the lines decreasing exponentially from the center frequency. Cumulative distributions of the sound pressure squared are presented and discussed at both the particular frequencies of the lines of the spectra and at the entire frequency band of the sound. The effect of the various shapes, positions, and speeds of the vane on the variance of the sound pressure squared, averaging: over different microphone travel paths, and autocorrelation relations of the sound field were also investigated. Practical conclusions for the sound power measurements in reverberation chambers are presented and discussed. The applicability of the existing formulas for the calculation of the variance of the sound pressure of the multitonal sound ...

Intensity Function of the Cochlea and Cortex

Abstract: Amplitude changes of the cochlear potential due to increases in sound intensity were compared in the same animals with amplitude changes in the evoked potential from the cortex. As is well known, the cochlear potential is linear over a 30–50 dB range. Above this linear region, the cochlear potential plateaus, and then it actually declines when the sound intensity is further increased. The cortical‐evoked potential behaves in a similar manner. The amplitude of the cortical‐evoked potential increases monotonically with increases in sound intensity as long as the response of the cochlea is linear. When the cochlear potential departs from linearity, the increases in the evoked potential also tend to plateau. At the point the cochlear potential decreases in response to an increase in sound, the evoked potential from the cortex also decreases. This decrease in the amplitude of the evoked potential stresses the need for careful measurement of the sound intensity and/or the cochlear potential. In several studies, units have been observed to be inhibited by loud tones. True neural inhibition can be differentiated from overdriving the cochlea only if the proper measurements are made.

Relations among loudness, loudness level, and sound pressure level

Abstract: Numerical analysis of loudness, loudness level, and sound-pressure level of pure tones of steady noise that does not exceed critical bandwidth

The Helmholtz Huygens Integral

Abstract: The sound intensity inside a given volume is determined by the power of the sound sources inside this volume and by the sound intensity that enters the volume from outside. It is apparent that the expression for the sound field will be determined by the contributions of the sources and by boundary terms, which represent whatever is reflected at the boundaries or enters through the boundaries from outside. In deriving a formal solution, Green’s formula and Gauss’ theorem are of particular importance.

Theoretical predictions of supersonic jet noise

Abstract: Analytical predictions of supersonic jet noise, considering acoustic intensity, directivity, refraction, convection and peak Strouhal number