ISSN:0001-4966    

DOI:10.1121/1.1906863

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The total absorption for theater chairs with back and seats upholstered in mohair has been measured from 250 to 9000 cps in the Defense Research Laboratory reverberation chamber. Values are given for the chairs with (1) seats up, (2) seats down, and (3) occupied by adults.

ISSN:0001-4966    

DOI:10.1121/1.1906864

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The acoustic treatment of an excessively reverberant civic coliseum is described. Before treatment the structure, originally an aircraft hangar, had a sharply peaked reverberation time of eight seconds in the region between 600 and 800 cycles per second. Thirty‐two thousand square feet of two‐inch‐thick Fiberglas panels were suspended in horizontal V's six feet below the parabolic metal ceiling. After treatment, the reverberation time is essentially uniform from 100 cps to 800 cps, with an average value of approximately 1.2 seconds. The method of construction and the mounting of the panels is described. Sound absorption coefficients for these panels are given, and a comparison made between the value obtained from the coliseum installation and the value obtained for 72 square feet of identical panel hung in the Defense Research Laboratory polycylindrical reverberation chamber.

ISSN:0001-4966    

DOI:10.1121/1.1906865

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The transformer action of the middle ear as measured by Bekésy is shown to be the principal cause for the low acuity of hearing for low frequencies. Because of the very low mechanical impedance across the basilar membrane at low frequencies, large acoustical pressures in front of the ear drum produce appreciable acoustical pressures across the basilar membrane. For example, at 100 cps this pressure is 30 times and at 6000 cps it is 1/10 that created across the basilar membrane.

ISSN:0001-4966    

DOI:10.1121/1.1906866

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

After an ear is exposed to an intense sound, the absolute threshold for many sounds is raised, usually temporarily. The manner in which the absolute threshold recovers to its normal value after such stimulation is the subject of these experiments. It is found that recovery from such auditory fatigue is not a simple monotonic process. Rather these experiments show that under certain conditions the threshold first recovers to an approximately normal value about 1 minute after the cessation of the exposure but then rises again to a higher value that reaches a maximum at about 2 minutes after the exposure. This diphasic recovery curve, with its characteristic “bounce,” is found when the exposure involves sound pressure levels between 100 and 120 db and durations of the order of several minutes.Recovery curves are shown for the auditory thresholds of clicks, bands of noise, and pure tones. Fatiguing stimuli include bands of noise and pure tones.Two subsidiary observations are also reported. First, in many recovery curves there is evidence for a second “bounce” or rise in the threshold after stimulation. Second, after stimulation by moderate intensities the initial recovery (about 1 minute after stimulation) may demonstrate facilitation, i.e., a temporary reduction in the absolute threshold below the normal value. Qualitative observations concerning the pitch and timbre of the test stimuli and of tinnitus following stimulation are related to some of the data.

ISSN:0001-4966    

DOI:10.1121/1.1906867

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Opening and closing the mouth increases the sound pressure produced by bone conduction in the closed auditory canal by as much as six to ten decibels in the frequency range between 40 cps and 700 cps. This difference is explained by vibrations of the lower jaw relative to the skull. The resonance curve of this motion was measured and used to calculate the influence of the lower jaw motion on the sound level in the closed auditory canal. The results show that the measured frequency response of the difference in sound pressure open mouthvsclosed mouth, may be explained entirely by vibrations of the lower jaw.

ISSN:0001-4966    

DOI:10.1121/1.1906868

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

When a pure tone is mixed with a noise of uniform spectrum, its threshold is raised. At levels above threshold, its loudness and pitch are changed by the presence of the noise. Introducing abrupt changes in the slope of the noise spectrum by filtering out (rejecting) one octave changes these effects in the vicinity of this gap.The masked threshold for a pure tone varies from the value for unfiltered noise at the edges of the gap to a value approximately 25 db lower at the middle. This indicates that gapped‐noise may be used to mask out sounds outside of the gap without unduly raising the threshold of sounds in the gap.Presence of white noise.generally raises the pitch of a pure tone whose frequency is between 500 and 4000 cps. Presence of noise with the gap doesnotraise the pitch of a pure tone located in the upper half of the gap. For a tone located in the lower half of the gap, the pitch is raised more than it would be in the presence of unfiltered noise.The changes in the judged loudness of pure tones partially masked by a gapped‐noise reaffirm the importance of the tails of the excitation pattern in their effect on loudness.

ISSN:0001-4966    

DOI:10.1121/1.1906869

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Half‐loudness adjustments have been obtained from 18 observers at 10 intensity levels from 10 to 100 db. Adjustments were made with two methods. An analysis of variance of the attenuation scores necessary for half‐loudness showed: (1) Intensity accounted for a quarter of the variance. This variance indicates the extent to which the attenuation necessary for half‐loudness varies with different intensities. (2) Consistent differences between observers accounted for 35 percent of the variance, indicating that some observers consistently require much greater or less attenuation for half‐loudness than others. (3) One‐tenth of the variance was a result of the fact that the shape of the half‐loudness function with respect to intensity was different for different observers. (4) The error variance, caused by repeated adjustments by the same observer at the same intensity and with the same method, was 22 percent of the total. (5) Other variances were practically insignificant. The average half‐loudness function differs markedly from previously reported results. It is suggested that this discrepancy, as well as the large differences between individuals, is largely a result of the fact that observers have difficulty establishing the correct fractional value, and thus are extremely susceptible to indirect suggestion. A means of avoiding this problem of a nonvalid fraction is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1906870

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The most comfortable listening level and the range of comfortable listening levels for pure tones were determined for a group of normal (nonclinical) listeners in the quiet and against various levels of background noise. In general, the most comfortable listening (mcl) level contour has the general shape of the equal‐loudness contour at intermediate loudness levels—lowest intensity at the middle frequencies and highest intensity at the lower frequencies. The range of listening levels considered “comfortable” against a quiet background varies from about 20 db at the lowest frequencies to about 35 db at the middle frequencies. The variability of the mcl is larger at high frequencies than at low frequencies, and it is about the same magnitude as the variability of heterophonic equal‐loudness matches. The effect of noise is primarily to raise the lower limit of the range of comfortable listening levels and only secondarily to raise the upper limit. As a result, therangeof comfortable listening levels is decreased in noise. The possible use of the comfortable listening level test as a gross diagnostic tool in the detection of nerve‐type deafness is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1906871

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Albino mice were tested for susceptibility to audiogenic seizures in sound fields of various frequencies and intensities. An attempt to fix the ears of the mice with respect to the sound source by suspending the mice with a large spring clip which grasped the dorsal skin‐fold proved fruitless, for too few seizures were induced at any intensity. The mice were therefore tested in a small wire mesh cage suspended in front of the sound‐transducer, and the positions of their ears during the treatment were recorded. At 10 kc, at least 92 db was needed to induce seizures in mice which had no previous seizures, while only 83 db were needed for animals which had previous seizures. The most effective frequencies for the induction of seizures were between 12 and 25 kc. Below 10 kc, the effectiveness dropped off sharply and was very low at 5 kc. Studies were not made above 25 kc. The peak of the mouse's audiogram is probably near the frequencies which are most effective for induction of seizures and is thus a little lower than that of the rat and about 1.5 octaves above that of man. The ability of mice to hear at frequencies which are ultrasonic for the human ear is probably the reason for the intense reactions of mice to complex sounds which seem of moderate intensity to man.

ISSN:0001-4966    

DOI:10.1121/1.1906873

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP