摘要:

The cochlear microphonics and the auditory action potentials of guinea pigs, under anaesthesia, were recorded with differential electrodes. The ears were exposed to pure tones of frequencies 185, 545, 2000, or 8500 cps at intensities sufficient to cause severe acoustic trauma within one to six minutes. The cochleas were immediately fixed and subsequently studied microscopically. Good correlations were obtained between the immediate depression of electrical activity and the severity of anatomical injury. Electrical depression at any given position of electrodes in the cochlea was substantially constant regardless of the frequency of the test tone. Action potentials disappeared before the cochlear microphonic. Exposures above 145 db, measured at the animal's eardrum with a probe‐tube microphone, for more than half a minute regularly caused severe anatomical injury to the organ of Corti, often including gross rupture. Rupture begins at certain well‐defined points in the organ of Corti. The external hair cells are the most susceptible structures, but in the middle turns of the cochlea rupture may follow closely. The injury was greatest in the apical turns from 185 and 545 cps and in the basal turn for 8500 cps.

ISSN:0001-4966    

DOI:10.1121/1.1917594

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Criteria are presented to guide the specification writer in setting limits on airborne noise in shipboard spaces of U. S. Navy vessels. Limits are given for three objectionable effects of airborne noise: (1) permanent hearing loss, (2) interference with speech communication, (3) discomfort. The limit for any specific ship space depends on which, if any, of these effects can be tolerated without interfering with the function of the space. Limits for hearing loss and discomfort are expressed in terms of octave‐band spectra. The hearing‐loss‐avoidance limit is that suggested by Hardy. The comfort limit is based on criteria of Lippert and Miller. The limits for interference with speech are expressed in terms of the “speech‐interference level,” i.e., the arithmetic average of the levels in the 4 octave bands covering 300 to 4800 cps, following the scheme of Bolt, Beranek, and Newman. Maximum permissible speech‐interference levels are tabulated as a function of the distance to the speaker, the voice level, and the acoustic absorption in the space. For typical ship spaces, tentative noise‐level limits are suggested, based on present usage of the spaces.

ISSN:0001-4966    

DOI:10.1121/1.1917600

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

In determining the efficiency of a transducer it is desirable to know whether some of the electrical energy is expended in a pumping action at the transducer surface, as distinguished from the hydrodynamic flow due to absorption of energy in the medium. The force due to the total unidirectional flow from a plane‐wave transducer in water, acting upon a thin membrane placed at various distances, can be measured, together with the intensity of radiation passing through the membrane. The transducer is also suspended in the water in such a way that the total force reacting upon it can be observed. From these data and the losses in crystal and mounting, one can calculate how much of the applied energy goes into radiation. Experimental results are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917605

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Experiments have been conducted to determine the dependence of aural recognition of pulsed signals on the pulse length, signal‐to‐noise ratio, and the bandwidth of the filter through which the signal and noise were passed. The pulse lengths used ranged from one‐fourth second to four seconds, and the filter bandwidths ranged from one‐fourth cycle to one thousand cycles and were centered at eight hundred cycles. Signals randomly spaced in the noise background were presented to eight trained subjects. Least‐square estimates of the signal‐to‐noise ratios required for fifty percent signal recognition were made, and their values were plotted as a function of pulse length and filter band width.

ISSN:0001-4966    

DOI:10.1121/1.1917617

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The travel time of sound across a fixed gap between diaphragms of transmitting and receiving transducers is recorded each 1/500 second. From this the interdiaphragm velocity is computed. It is a function of both temperature and wind. Spurious travel time changes introduced by phase shifts in the receiver are minimized by using a 500‐cps intelligence signal amplitude modulating a 10‐kc carrier. Experimental errors when operating in air with interdiaphragm distances of 3 feet are less than 2 percent in the temperature range from 70° to 200°F, but the application of the instrument is not restricted to this range. A circuit for recording velocity directly on a paper tape is described. Although designed primarily for air, the unit is readily adaptable to other media. It should also be of special interest to the micrometeorologist.

ISSN:0001-4966    

DOI:10.1121/1.1917620

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

It has been shown by Thuras, Jenkins, and O'Neil that the theoretical magnitude of the extraneous frequencies, generated in air by very intense sounds, are obtained from an approximate solution of the exact differential equation of wave propagation in air. The solution shows that the pressure of the extraneous harmonic frequencies generated in air increases with (1) the frequency of the fundamental, (2) the magnitude of the fundamental pressure, and (3) the distance from the source. Taking into consideration the loss at the side walls of the tube in which the plane wave is propagated, we may write the ratio of the pressure of the generated second harmonic to that of the fundamental pressure asP2/P1 = KP0XR, whereK = (√/4) (γ+1/γP0) (ω/c),P0is the rms pressure of the fundamental atX= 0,Xis the distance from the source,Ris the loss factor1 minus; (α2X/2), α2is the loss per unit distance in the second harmonic pressure. It was found that the loss along the tube was essentially that at the side walls of the tube. This was expressed by Beranek asα equals; 3.18 × 10−5 (f12/r) nepers/cm, wherefis the frequency andris the radius of the tube. Thuras, Jenkins, and O'Neil found the absolute magnitude of the generated tones in the tube, of all measured values, to be about 3 db lower than the theoretical values. In this restudy of the problem, done under a Naval Research contract at U.C.L.A., it was found that the measured values of the generated second harmonic pressure were in good agreement with the theoretical values.

ISSN:0001-4966    

DOI:10.1121/1.1917627

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The present paper presents the preliminary results of a program of study which has been started to study sounds of aerodynamic origin. The spectra of noise generated in a miniature blow down subsonic tunnel are compared with the results of a survey on wind‐tunnel noise. The comparison indicates a substantial similarity between the spectra obtained and a tentative figure for the efficiency of noise conversion has been indicated.

ISSN:0001-4966    

DOI:10.1121/1.1917634

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP