摘要:

The Composer's Music Box is an electro‐acoustic tone generator producing single tones. It is played in much the same way as a musical score is written. It has a pitch range of about an octave and an intensity range of about 40 db. Electrical circuits provide nearly constant tone structure independent of the fundamental frequency, and provide considerable variation in attack and decay times.

ISSN:0001-4966    

DOI:10.1121/1.1906500

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

If we assume that in the evolution of the mammalian ear nature has made the best possible use of physical and acoustic principles, we are led further to assume (1) that the middle ear provides maximal sensitivity combined with optimal quality and (2) that the middle ear is so adjusted as to minimize noise pick‐up from the speaker's body during talking. In terms consistent with these assumptions, it is possible to explain: why mammals have two vocal cords; why a bony rod lies on the eardrum; why the point of rotation of this bony rod is at the edge of the eardrum; why the mass of the ossicles appears so exaggerated; why the eardrum is conical in shape; why the membrane of the footplate of the stapes is so small; why the footplate of the stapes has an elliptical form; why a joint is necessary between the stapes and the incus; and why an animal with thin head bones has a bulla.

ISSN:0001-4966    

DOI:10.1121/1.1906501

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

An experimental technique was developed to measure, for intact middle and inner ears, the volume displacement of the fluid in the cochlea produced by a given sound pressure on the eardrum. In order to determine whether it is possible to immobilize the stapes by increasing the static pressure in the cochlea, the transmission characteristics of the eardrum‐to‐round‐window system were measured with the ear under the maximum static pressure that can be produced in the cochlea without bursting the blood vessels. Since no important change in transmission was observed, it was concluded that immobilization of the stapes cannot be produced by an increase in static pressure in the cochlea.With the same technique the mechanical impedance of the movements of the stapes footplate, the round window, and the fluid in the cochlea were measured singly and combined as in the normal ear. Once the elastic properties of the cochlear partition were known, it was possible to construct an ear model that exhibited patterns of vibration similar to those found in the cochlear partition of the human ear. By changing the shape, the size, and the fluid viscosity in this ear model the relative importance of the different parts of the inner ear were studied.These experiments made it plain that the pattern of vibration of the cochlear partition is determined primarily by the volume elasticity of the membrane and the fluid close to the membrane. Length, height, shape, and diameter of the cochlear canal do not influence the vibration pattern. A mathematical description of the hydrodynamic properties of the inner ear must take into consideration this independence of the physical dimensions of the cochlear canal.

ISSN:0001-4966    

DOI:10.1121/1.1906502

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

In order to determine the way in which mechanical analysis of frequency occurs in the cochlea, a technique was developed for preparing anatomical specimens. This technique made it possible to measure the amplitude of vibrations along the cochlear partition when the stapes was driven with pure tones. It made it possible, further, to determine how the amplitude of vibration at any given place on the cochlear partition varies with the frequency. The relation of amplitude of vibration at a given place to frequency gives a curve very similar to a resonance curve. We can then calculate the logarithmic decrement characterizing the vibrations of the cochlear partition. This log decrement is almost independent of frequency and has a value ofd= 1.3. The decay time of the vibrations of the cochlear partition was observed directly with a microscope, and the values obtained in this way agreed with those derived from the resonance curves. All the measurements have been made on preparations of the human ear.

ISSN:0001-4966    

DOI:10.1121/1.1906503

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Continuous recorded speech passages were presented against a background of white noise and against a quiet background. The effect of the noise on the loudness of speech was determined by having listeners adjust the level of speech heard in quiet to sound equal in loudness to an assigned average level of speech presented against selected levels of background noise. In general, it was found that (1) low noise levels produce a proportionately lower depression in the loudness level of speech than higher noise levels, (2) as a first approximation, however, the effect of noise on the loudness of speech is a function of the speech‐to‐noise ratio rather than of the level of the speech alone or of the noise alone, and (3) under none of the experimental conditions did white noise actuallyincreasethe loudness of speech (the “Egan effect”).The assumption that a given level of noise subtracts aconstantnumber of loudness units from speech (regardless of the level of the speech) was found to be fairly adequate in describing the experimental results.

ISSN:0001-4966    

DOI:10.1121/1.1906504

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Some 40 or more years ago, there was evidence of interest among scientists in the sounds of mosquitoes. Despite very crude acoustical apparatus, significant conclusions had been reached by the early investigators. Although very little was done in the next three decades despite the growth in the field of acoustics, interest has recently been renewed because of the world‐wide need to check the spread of mosquito‐borne tropical diseases. Recent experiments have confirmed many early findings and have provided valuable new data.Mosquito sounds are distinctive; gross differences occur that are readily detected both by listening and by wave analysis. All fundamental sounds occur in the center of the sonic range (200–1000 e.p.s.); all are rich in harmonics. All sounds are warble‐modulated, some at a single low rate in the order of 5 c.p.s., others at a double rate with the same lower rate and a higher rate in the order 5 times the lower. In some tones, some harmonics are completely interrupted while the fundamental remains undisturbed. Warble amplitudes are quite large; 20 percent is not unusual. The fundamental pitch often drifts; in one case, for example, there was a 25 percent increase in as little as 0.05 sec. Male sounds seem higher pitched than female; sound spectrograms show this to be due more to the difference in harmonic emphasis than to the difference in fundamental pitch. Generally speaking, mosquitoes do not generate or respond to sine‐wave tones.Mosquito sounds are low in energy level; the total sound power output of a female Anopheles albimanus whose sound was used to bait a mosquito‐killing trap in Cuba was in the order of 10−13watt. With this low power level it is difficult to obtain recordings with the high signal‐to‐noise ratios customary in high quality commercial recording because of the relatively high noise levels. Despite this handicap, it has been possible to reduce the noise due to microphonics, hum induction, vibration, and airborne and other disturbances to the point where recordings with 40‐db signal‐to‐noise ratio are made frequently.

ISSN:0001-4966    

DOI:10.1121/1.1906505

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906506

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906507

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.2142328

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP