摘要:

The acoustic properties of representative diving‐mask cavities were measured, using a high‐impedance sound source. Curves of impedance presented to the lips and of microphone transmission, relative to those of free space, were obtained. Both nonabsorbent cavities and cavities with standing‐wave absorption adaptable to a marine environment were investigated.

ISSN:0001-4966    

DOI:10.1121/1.1912608

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

As work progressed from the physical measurements reported in Part I [J. Acoust. Soc. Amer.50, 1–9 (1971)] to psychoacoustic testing, the gradient microphone proved not merely to perform somewhat better than the pressure microphone in diving‐mask cavities, but to be essentially insensitive to cavity acoustics. With the gradient microphone, no optimum cavity dimensions were found, and standing‐wave absorption within the cavity became unnecessary. These results were confirmed by sonograms and by response measurements with an artificial vocal tract.

ISSN:0001-4966    

DOI:10.1121/1.1912607

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

It is pointed out that a sinusoid satisfies Salmon's criterion for a good horn shape. Calculations have been made of the throat impedance of sinusoidal horns of various dimensions, including the case of a single globe terminating in a cusp. Depending on the relative dimensions at the mouth and throat, the device may be used as an impedance transformer. Experimental determinations of directivity of an underwater horn have been made and were found to compare favorably with conical horns. Finally, it is demonstrated that several musical instruments employ sinusoidal cavities, the bell of the English horn being discussed in particular.

ISSN:0001-4966    

DOI:10.1121/1.1912609

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Airport community noise exposure to jet aircraft takeoff and landing activity at Los Angeles International Airport (LAX) has been extensively measured and documented. However, the noise instrusion problems due to overflights of jet aircraft in the approach and departure air routes over the communities of the Los Angeles metropolitan area have largely been ignored. Preliminary measurements indicate that in at least 10 peripheral residential communities (at distances up to 15 miles from LAX) the noise levels caused by jet aircraft overflights exceed 20 dB(A) above the average ambient‐noise levels. There are four major approach and departure corridors to LAX with a total number of 500 commercial jet aircraft overflights each 24 hours. Many communities are thus subjected to about 100 overflights during the peak traffic periods (about three hours duration). As a result, hundreds of thousands of individuals are subjected to a significant noise annoyance every two minutes for sustained periods. In most of these instances, the noise levels exceed the municipal codes on allowable residential noise disturbances. However, these noise ordinances are not enforced against the air carriers. It is estimated that if the aircraft operators were fined accordingly, the total of such fines in the Los Angeles area would be a billion dollars per year.

ISSN:0001-4966    

DOI:10.1121/1.1912610

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

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 pressure, if aerodynamically generated noise is negligible. It provides a lower limit of sound pressure which can be detected by a microphone in an airflow. Moreover, the detection of noise generated by a grille in a duct is discussed by taking account of the characteristics of the microphone response to wind‐flow fluctuation.

ISSN:0001-4966    

DOI:10.1121/1.1912611

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1912612

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The past decade has witnessed the blossoming of many large, all‐encompassing structural analysis programs. We have now reached the stage where most self‐respecting organizations are using one or more such programs. An enormous amount of effort has been spent on developing these programs. It is, perhaps, time to reflect on the degree to which the original objectives have been achieved. Has the effort expended been justified, and what changes in objectives might now appear desirable? What is the position of the smaller organization with more limited resources? The paper attempts to resolve these questions and to advance suggestions as to what our future objectives should be.

ISSN:0001-4966    

DOI:10.1121/1.1912613

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Contemporary urban planning and building design for single and multiple dwellings to be located in areas of high level noise are only now beginning to account for the planning, legal, and architectural constraints that perpetrate inadequate isolation from exterior noise at every price level. Current exterior construction and glazing techniques provide little basic isolation. Conventional penetration of the exterior for air conditioning intakes, vents, kitchen and bathroom exhausts, and attic vents would, in any case, destroy the effectiveness of a well‐designed exterior. To add to the designers problems, modern urban planning has, to date, been more concerned with social and civil engineering aspects of site evaluation. Working toward correcting this situation some planning, architectural, and engineering activity is under way. Several major airport regions and highway projects have been evaluated on a noise basis as part of the planning. Among architectural ideas that have been developed are wall systems. These include cavity walls of medium density block, fenestration designs for a high‐rise as well as single‐family housing using a minimum of exposed glass for maximum light, and roof designs that optimize acoustical isolation in thermally appropriate exterior systems. Finally, control of inadvertant penetrations of the building combined with operable closures that really close, can, along with the other measures cited, improve interior isolation 15 and possibly 20–25 dB over conventional building design.

ISSN:0001-4966    

DOI:10.1121/1.1977746

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

This paper describes a series of acoustical isolation designs affecting the building shell and its required penetrations for office occupancy, from jet runways where aircraft under takeoff conditions pass within 150 ft of subject building. Outside sound‐pressure levels on building roof together with inside sound‐pressure levels will be presented for the completed structure.

ISSN:0001-4966    

DOI:10.1121/1.1977748

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The difference threshold for intensity of tactile stimuli was measured using a 2IFC procedure. Two types of tactile stimuli were delivered to the right index fingers of Ss: (1) taps, approximately 10 msec in duration, and (2) 200‐msec bursts of sinusoidal vibration, 160 Hz. Difference thresholds were measured at stimulus intensities of 14, 21, 28, and 35 dB SL. Difference thresholds for taps were higher at lower intensities than the difference thresholds measured at the same intensity for the bursts of vibration. Difference thresholds were also measured for taps and bursts in the presence of extraneous vibration. The difference thresholds were elevated when signal intensities were low and the extraneous vibration was strong. The extraneous vibration raised the difference threshold for bursts more than for taps. These results may be compared to results obtained by Raab and Taub [J. Acoust. Soc. Amer.46, 965–968 (1970)] with auditory stimuli in which the presence of noise under some conditions caused a reduction in the difference threshold for clicks.

ISSN:0001-4966    

DOI:10.1121/1.1977754

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP