摘要:

The recently opened Segerstrom Hall in Orange County, California is a 3000‐seat directed reflection sequence (DRS) hall that responds in a unique asymmetrical way to the competing demands for theater and symphony. This paper reviews the origins of this concept, the design process by which it was realized, and the model study at 1:10 scale carried out in New Zealand. Comparisons between modeled results and final results in the hall will be presented.

ISSN:0001-4966    

DOI:10.1121/1.2023695

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Considerable attention has been devoted in recent years at various technical meetings, including the 112th ASA Meeting, to the room acoustics design of the main theater of the Orange County Performing Arts Center in Costa Mesa, CA. In addition to the 3000‐seat multi‐use hall, there are four rehearsal spaces and numerous support facilities. This complex project has required a very large and thorough consulting effort in terms of sound isolation and mechanical‐systems noise and vibration control in addition to room acoustics design. This paper will discuss the overall building complex, details of specific support facilities, and many interesting aspects of the consulting process that have made this project unique.

ISSN:0001-4966    

DOI:10.1121/1.2023739

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Ultrasound irradiation, used in either continuous or pulsed mode, at a frequency of 0.75 MHz and spatial‐temporal average intensities between 60 and 1000 mW/cm2, has been shown to produce stable gas bubbles in the tissues of experimental animals [S. Daniels and G. R. ter Haar, Proc. Inst. Acoust.8, 147–154 (1986); G. R. ter Haar, S. Daniels, and K. Morton, IEEE Trans. UFFC‐33, 162–164 (1986)]. Macroscopically visible bubbles are also produced in agar gels during irradiation with ultrasound at the same frequencies and intensities used with experimental animals. The effect on the number of bubbles formed of varying ultrasonic frequency, intensity, pulse length, and duty cycle as well as ambient temperature is similar in the gels to that in animals. Many of the aspects of bubble formation in gels have been explained in a qualitative manner by a theoretical model based on growth of a cavitation nucleus by rectified diffusion. This may provide a useful theoretical basis for the explanation of bubble formation invivo. [Work supported by MRC (UK), NSF, ONR, NIH, and CRC/MRC Joint Committee program support for the Physics Department, Institute of Cancer Research.]

ISSN:0001-4966    

DOI:10.1121/1.2023783

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Human lymphocytes were exposed to an ultrasound pulsing regimen similar to that typically employed in clinical Doppler measurements of fetal blood flow, to determine whether such pulses were able to alter the frequency of sister chromatid exchanges (SCE). A 3.1‐MHz, 1.5‐cm‐diam transducer emitted 5‐ to 50‐cycle pulses in a beam that was directed vertically along the axis of a stationary tube containing the blood suspension. Hydrophone measurements within the tube showed that the beam intensity profile was maintained beyond the free field focal region, thereby ensuring maximum exposure of the contents of the tube. A significant increase in SCE frequency was observed in blood from two random donors exposed to “diagnostic” levels of ultrasound, where the SPTA intensity ranged from 1 to 4 W/cm2. However, a number of further studies on blood from a single (different) donor have failed to show any effect from ultrasound even after an exposure dwell time of 24 h. This extraordinary finding may have some relevance towards explaining some of the controversial reports of SCE induction in human lymphocytes. Research continues to try to identify the mechanisms responsible for this effect.

ISSN:0001-4966    

DOI:10.1121/1.2023832

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

In many practical engineering systems, it is important to understand the physics of interacting subsystems, some of which lend themselves to lumped representations while others are inherently distributed. The noise and vibration caused by the engine of an automobile is a good example. The engine, the source of the vibrational and acoustical energy, is a lumped system for typical operating speed. However, the engine sits atop the vehicle frame structure, which exhibits modal dynamics. Ultimately, the vibrational energy finds its way to surfaces that radiate acoustic energy to the surroundings. If one were to model this overall system, lumped and distributed dynamic effects would have to be included. Bond graphs are a concise pictorial representation of the energy storage, exchange, and dissipation mechanisms of dynamic engineering systems [R. C. Rosenberg and D.C. Karnopp,Introduction to Physical System Dynamics(McGraw‐Hill, New York, 1983)]. Considerable work has been done in developing bond graph methods for the modal dynamics of distributed systems [D. L. Margolis, “Bond graphs, normal modes, and vehicular structures,” Veh. Syst. Dynam.7(1) (1978) and D. L. Margolis, “A survey of bond graph modeling for interacting lumped and distributed systems,” J. Frankin Inst.319(1/2) (Jan. 1985)]. The virtues of bond graph modeling are many and space is short; however, once a bond graph model has been constructed, then physical state variables are dictated, and the system can be automatically simulated using a digital computer. This applies to nonlinear as well as linear systems except that the distributed aspects of the overall system must be linear. The paper will develop bond graph modeling for lumped and distributed systems, and the procedure will be demonstrated for realistic systems.

ISSN:0001-4966    

DOI:10.1121/1.2023880

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Traditional models of sensors and actuators typically represent the transducer by a series of interconnected, discrete, lumped elements. Such models are useful because the characteristic behavior of the transducer is described by ordinary differential equations. However, these models are limited to low‐frequency regimes because they contain a finite number of elements. Further, they are not easily adaptable to transducers in which the behavior is explicitly a consequence of the continuum nature of transducing element, such as acoustic horns. Presented here are generic models of transducers in which the continuous nature of the transducer is stressed. The models may be classed into two types: those which apply to transducers in which the coupling between locations occurs only through the input and output ports, and those in which there is mechanical coupling between transducer locations as well. The former case may be modeled using coupled two‐port theory, and the latter using augmented transmission lines. These techniques allow for spatially varying physical parameters, and apply regardless of the transducer type, function, and geometry.

ISSN:0001-4966    

DOI:10.1121/1.2023926

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

The generation of noise by turbulence in the tip region of a blunt‐tipped, lifting airfoil was studied. Data were collected on surface and farfield sound pressures in the NASA Ames 2.13 × 3.05 m (7 × 10 ft), subsonic wind tunnel using an NACA 0012 wing section of aspect ratio 2.67, at an angle of attack of 16 deg. The contributions of particular source regions were determined using cross‐correlation techniques on surface and farfield sound pressures. Clipping the recorded signals prior to correlation allowed the isolation of radiated sound levels up to 25 dB below the tunnel background levels within a reasonable record length. The results indicate that in the case of blunt‐tipped airfoils there is a significant noise source in addition to the separated flow under the tip vortex (on the upper wing surface) predicted by other investigators. The characteristics of these two sources of noise are presented and comparison made with existing theories and prediction schemes. [Work supported by NASA Ames Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.2023983

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

JWA has not been in compliance with the California Airport Noise Standard for many years. A variance process allows California airports to operate out‐of‐compliance and the state does not consistently or vigorously enforce the process or the regulations. A great many single‐family residences are located within the excessive noise zone near the airport. The principal method used by the county to “reduce” the noise is to condemn the properties. Restrictions on commercial jet aircraft operations are also imposed that are supposed to prevent any increase in the size of the excessive noise zone. However this is a flawed process based on inconsistent reasoning that leaves an excessive noise impact unmitigated. This is because the allowable noise limit is too high, the noise zone area is inherently inaccurate, and the noise monitoring and impact rating procedures ignore significant considerations. For example, even if all commercial jet operations were terminated, the noise impact would still be excessive due to commuter and private aircraft operations.

ISSN:0001-4966    

DOI:10.1121/1.2024028

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

By using a global theory of sound propagation in a circular duct with a dissipative material, the equivalent acoustical impedance of the cross section of the duct was calculated at low frequencies. Plane wave theory was then used to calculate the four‐pole parameters of the duct using empirical formulas of the propagation constant and specific impedance of a dissipative porous material. The insertion loss of a single chamber dissipative muffler was calculated for different geometries and dissipative materials, and the insertion loss was measured using two microphone probes and white noise. The measurements were performed with different geometries and with different porous materials. The acoustical properties of the porous materials were calculated on the basis of the measured flow resistance and the calculated acoustical properties were compared with results obtained by using a standing wave tube method. A good agreement was found between the calculated and measured insertion loss of the single chamber dissipative muffler in the frequency range below the cutoff frequency of the muffler.

ISSN:0001-4966    

DOI:10.1121/1.2024087

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP

摘要:

Whenever we are dealing with noise propagation at distances greater than 100 m from the source, there are many factors affecting the propagation. For weapons firing, a major factor affecting propagation is the tendency of terrain to diffract and deflect the sound. A computer program has been written in TurboPASCALto run on an IBM‐XT computer. The program consists of digitized terrain data for a specific area along with a predictive sound propagation model for 25‐ and 7.62‐mm guns along with the TOW anti‐tank missile. The user selects locations of firing point, target point, and observer, along with number of rounds fired, and the start and end time of firing. The computer program provides the A‐weighted day‐night average sound level at the observer's location. The significant feature ofNOISE.PASis that it computes excess attenuation caused by terrain for specific sites. Additionally,NOISE.PAStakes the tedium out of doing sound calculations, which incorporate excess attenuation caused by terrain, for weapons firing.

ISSN:0001-4966    

DOI:10.1121/1.2023549

出版商:Acoustical Society of America    

年代:1986

数据来源: AIP