Showing papers on "Sound transmission class published in 1984"

On the Absorption of Sound by Turbulence and Other Hydrodynamic Flows

Abstract: The dissipation of acoustic energy which occurs when sound generates vorticity at the boundaries of a fluid or propagates across a field of turbulence is examined. Vorticity generation occurs typically during scattering or diffraction by surfaces with corners or edges, and an understanding of the consequent attenuation is important in the design of mufflers and other devices used for suppressing acoustic and mechanical vibrations. The rate of dissipation is generally a nonlinear function of the acoustic intensity, but becomes linear and significantly greater in the presence of a mean flow.

Transient and multiple frequency sound transmission through perforated plates at high amplitude

Abstract: The transmission of complex periodic and transient acoustic signals through orifice plates at high amplitude, and in the absence of mean fluid flow, is discussed. A simple fluid dynamical model, involving a time‐varying mass end correction, is the basis of the theory. The equation of motion for the air in the orifice is solved numerically in the time domain. For a specific instance, an analytical solution in the frequency domain is possible. Good agreement is noted between experimental and theoretical results in both time and frequency domains.

Prediction of Structure Borne Sound Transmission Using Statistical Energy Analysis

Abstract: Statistical Energy Analysis (SEA) is applied to analyze structure-borne sound transmission in complex structures.The system equation describing the energy flow in the structure is derived by the network formulation, and for saving the computational time, approximated formulae for SEA parameters are found.Measured and calculated results are fairly good agreed for 3D-plate structures, including a scale model of ship structure.Furthermore, the acousto-structural coupling problem is investigated, experimentally and theoretically, for both cases without and with additional absorbing treatment. From results, the measures for reducing the response in the receiving element and the effect of the treatment are shown.

Propeller aircraft interior noise model utilization study and validation

Abstract: Utilization and validation of a computer program designed for aircraft interior noise prediction is considered. The program, entitled PAIN (an acronym for Propeller Aircraft Interior Noise), permits (in theory) predictions of sound levels inside propeller driven aircraft arising from sidewall transmission. The objective of the work reported was to determine the practicality of making predictions for various airplanes and the extent of the program's capabilities. The ultimate purpose was to discern the quality of predictions for tonal levels inside an aircraft occurring at the propeller blade passage frequency and its harmonics. The effort involved three tasks: (1) program validation through comparisons of predictions with scale-model test results; (2) development of utilization schemes for large (full scale) fuselages; and (3) validation through comparisons of predictions with measurements taken in flight tests on a turboprop aircraft. Findings should enable future users of the program to efficiently undertake and correctly interpret predictions.

Arctic acoustic propagation model with ice scattering

Abstract: : An underwater sound propagation program has been adapted to Arctic use. The program enables computation of the coherent sound field with normal modes and the incoherent surface scattered field by integrating over ray paths from the surface to the source and receiver. For Arctic use, ice scattering and ice loss functions have been developed by comparing computed losses with Arctic propagation loss data. The sensitivity of the computed losses to the form of the scattering function is determined for one frequency. A difference in ice loss between summer and winter is hypothesized, but the data are insufficient to check the hypothesis.

Low-frequency sound absorption measurements in air

Abstract: Thirty sets of sound absorption measurements in air at a pressure of 1 atmosphere are presented at temperatures from 10 C to 50 C, relative humidities from 0 to 100 percent, and frequencies from 10 to 2500 Hz. The measurements were conducted by the method of free decay in a resonant tube having a length of 18.261 m and bore diameter of 0.152 m. Background measurements in a gas consisting of 89.5 percent N2 and 10.5 percent Ar, a mixture which has the same sound velocity as air, permitted the wall and structural losses of the tube to be separated from the constituent absorption, consisting of classical rotational and vibrational absorption, in the air samples. The data were used to evaluate the vibrational relaxation frequencies of N2 and/or O2 for each of the 30 sets of meteorological parameters. Over the full range of humidity, the measured relaxation frequencies of N2 in air lie between those specified by ANSI Standard S1.26-1978 and those measured earlier in binary N2H2O mixtures. The measured relaxation frequencies could be determined only at very low values of humidity, reveal a significant trend away from the ANSI standard, in agreement with a prior investigation.

Remotely controllable arrangement for adjusting the balance in the sound transmission part of an arrangement for reproducing a stereo sound event

Abstract: In an arrangement for stereo reproduction of a sound event with an arrangement for automatic adjustment of the balance for the instantaneous listening location, a sound transmission part (2) of the arrangement contains a test sound source (12), which can be switched in a test sound operating mode into the sound channels (L, R) instead of the useful stereo sound source upstream of the signal inputs (9, 10) of the balance adjuster arrangement (8). The associated remote control transmitter (1) additionally contains a balance control arrangement (30) with a sound receiver arrangement (31) for receiving the test sounds at the listening location, a selection device (32) which forwards the received test sound signals to the two reception channels (36, 37) associated with the test sound signals and assigned to the sound channels of the sound transmission part, a measuring circuit (33) which generates output signals proportional to the volume at the listening location and a comparator arrangement (34) which, if the output signals on the reception channels are not identical, produces a corresponding adjustment command (BL or BR) to the adjustment inputs (15) of the balance adjuster arrangement. With an arrangement of this type, even an unskilled listener can at any time easily achieve perfect balance adjustment for a stereo transmission at his listening location.

Shear-layer correction after Amiet under consideration of additional temperature gradient. Working diagrams for correction of signals

Abstract: Amiet's correction scheme for sound wave transmission through shear-layers is extended to incorporate the additional effects of different temperatures in the flow-field in the surrounding medium at rest. Within a parameter-regime typical for acoustic measurements in wind tunnels amplitude- and angle-correction is calculated and plotted systematically to provide a data base for the test engineer.

Foreign matter detector for core metal of steering wheel

Abstract: PURPOSE:To enable standardization for accepted and rejected products with a simple detection of foreign matters in the core by arranging the base part of a holder section for holding a steering wheel core and the base part of a sound transmission plate to turn freely, a detector section on the sound transmission plate and a display section connected thereto. CONSTITUTION:An inspector hangs a steering wheel core metal 9 on hook-shaped parts at two points of a holder section 4 and when a hand is released, the steering wheel core metal 9 is displaced vertically from the hook-shaped holder section 4 by own gravity while the lower end thereof 9 always gets into contact with the lower end of a sound transmission plate 5 as the sound transmission plate 5 tilts slightly on the side opposite to the side where a support 2 exists. Under such a condition, when the holder section 4 is swung on the mount shaft 3 with the core metal 9, foreign matters, if any, gather to the bottom of the core metal 9 and hit the inner side wall of the hollow core metal 9, causing an abnormal sound. When there is none of the abnormal matters, no abnormal sound. When there is none of the abnormal matters, no abnormal sound is caused. The presence and magnitude of abnormal sounds are transmitted to the detector section 6 and a display meter section 7 through the sound transmission plate 5 whereby the presence or the like of the foreign matters is indicated on the display meter section 7 to detect.

Comparison of laboratory and field sound insulation measurements of party walls and facade elements

Abstract: In the present work, eight party walls and facade elements have been measured in laboratory and field conditions. Lab measurements were carried out in a horizontal chamber, with flanking transmission, that basically fulfills the requirements of DIN 52210/2 standard. Field tests were performed in real dwellings, with typical furnishings and linings. The installation of samples was carefully controlled, in order to reproduce similar mountings in both situations. Velocity measurements were made during field tests in order to define the principal paths of sound transmission. Leaks were avoided in each case. The overall variability of tests was determined from the study of random sources of error. For this purpose, two operators made three replications under the same environmental conditions, with the same instrumentation for each measuring sample. To the contrary, both operators did each set of replicates, at long intervals of time with different equipment. Finally, a correlation between lab–field results was found. The fitted straight line shows that field results are systematically lower than lab results, and the resulting differences tend to rise with increasing insulation values.

Nonlinear propagation in a depth-dependent ocean

Abstract: : The propagation of finite-amplitude sound in a depth-dependent ocean has been studied analytically and numerically, using a model based on weak-shock theory and the high frequency ray approximation. Results are presented for the equivalent propagation distance, in a uniform ocean, which reproduces the nonlinear distortion in the real situation. Numerical results for typical ocean properties are collapsed by means of an asymptotic theory, for ray paths along which the sound speed increases or decreases monotonically. Results are also shown for rays which form caustics.

Development of Computer Programs Using the Method of Images to Predict the Sound Field in a Wedge Overlaying a Fast Fluid and Comparison with Laboratory Experiments.

Abstract: : Two computer programs using the method of images to determine the pressure amplitude and phase distribution in a wedge shaped medium overlaying a fast fluid bottom were studied. WEDGE used a source at infinity and was constrained to upslope, on axis predictions, while CROSS SLOPE, using a source at finite distance, made predictions anywhere within the medium. Comparison of the two programs suggest that an infinite source is not approached until the source exceeds six hundred dump distances from the apex. CROSS SLOPE prediction of pressure amplitude were in agreement with experimental data obtained in the upslope direction, and with sound field similar to that described by the theory of Buckingham but of much richer variety. Additional keywords: thesis; Sound propagation; Shallow water; Fortran; charts. (Author)

Sound fields near building facades

Abstract: Measurement of sound transmission through the exterior facade of a building requires a determination of the incident sound power. Direct measurement of the sound field near the relevant surface seems preferable to the use of a `calibrated source' because of variability in outdoor propagation associated with ground reflections and atmospheric conditions. The interpretation of sound pressure level measurements in this environment is, however, complicated by the interference between incident sound waves and those reflected from building surfaces. This paper presents experimental results and a simple predictive model

The theoretical response of a vertical line array to wind-generated noise in shallow water

Abstract: : In this NATO-furnished report a wave-theory model for the propagation of noise from a surface source layer was used to investigate the directional response of a vertical array of hydrophones to wind noise in shallow water The model assumes an infinite layer of sources radiating sound with pressure directionality of the form COS (superscript m sub alpha), where m or = 1 and alpha is an angle measured from the downward vertical The field incident on the array is inhomogeneous and directional responses have been calculated from the (non-Toeplitz) spatial correlation matrix for various bottom types, sound speed profiles, and values of m up to 3 Results show that both components of the noise field - the discrete normal modes and the continuous spectrum - can contribute significantly to the total noise level and to the array response Shallow-water noise levels are found to exceed those of an idealized, infinitely-deep ocean by approximately the amount contributed by the discrete modes Furthermore, the discrete mode arrivals give high-array responses in near-horizontal steered directions Thus the directional response pattern produced can be of considerably different form from that predicted by a simple correlation model for ideal conditions The extent of these differences in both noise level and array response is strongly dependent on bottom type and on the value of the parameter m, and slightly dependent on sound-speed profile

General aviation aircraft interior noise problem: Some suggested solutions

Abstract: Laboratory investigation of sound transmission through panels and the use of modern data analysis techniques applied to actual aircraft is used to determine methods to reduce general aviation interior noise. The experimental noise reduction characteristics of stiffened flat and curved panels with damping treatment are discussed. The experimental results of double-wall panels used in the general aviation industry are given. The effects of skin panel material, fiberglass insulation and trim panel material on the noise reduction characteristics of double-wall panels are investigated. With few modifications, the classical sound transmission theory can be used to design the interior noise control treatment of aircraft. Acoustic intensity and analysis procedures are included.

Laser microphone device

Abstract: PURPOSE:To obtain an electric signal having high fidelity and a small amount of noise by detecting the change of the refractive index of air due to sound transmission with the diffraction intensity of laser light passing through said air and converting the change of said refractive index into an electric signal. CONSTITUTION:An air layer 2 vibrates in response to a sound wave 3 which propagates into the layer 2 from a sound source toward an arrow mark. The laser light of an angular frequency omega sent from a laser source 4 passing through a region of the layer 2 where the refractive index varies with an angular frequency OMEGA receives a phase modulation during the change of the refractive index of the layer 2. Thus a side band wave is produced in a range of omega+ or -nOMEGA (n: integers of 1, 2, 3...) on the basis of omega. In this case, the diffraction intensity of the laser light changes approximately in proportion to the change of the refractive index. Therefore the change of the output of the laser light 5 is detected by a photoelectric transducer 7 through a slit 6 pierced on the optical axis and delivered in the form of an electric signal. These electric signals are amplified by an amplifier 8 to reproduce a sound. This laser microphone device uses no diaphragm at all, and therefore an electric signal having high fidelity and a small amount of noise is obtained.

Two dimensional nonlinear analysis of sound transmission through a near-sonic throat flow

Abstract: A two-dimensional nonlinear theory of sound transmission through a nonuniform duct carrying a near-sonic throat flow is described. The mean flow in the duct is treated according to a generalized quasi-one dimensional model, and the analysis of the unsteady perturbations is carried out using the Method of Matched Asymptotic Expansions. The linearized acoustic field in the subsonic regions of the duct is approximated by a Wave Envelope model which is matched asymptotically with a nonlinear inner solution valid in the near-sonic throat region. Numerical results are presented to illustrate the predictions of the theory. It is found that, in general, shock waves develop in the acoustic field during transmission through the near-sonic flow. Unlike previous one-dimensional theories, the current study shows that dispersion can play a major role in the propagation process.

Frequency multiplex multichannel audio signal transmission system with intensity-modulated infrared radiation, especially for reproducing sound recordings on film copies apart from the original language, simultaneously in various other languages

Abstract: Multi-channel - in sound transmission frequency multi plex mode using intensity modulated infrared radiation, in particular to enable the transfer of sounds at Wied film prints, voice or singing performances other than the original language in gleichzei tig more other language versions. In this invention is a device for wireless transmission of multiple audio signals by means of Inf rarotstrahlung (7) (8) (9) (10) to a plurality of small, very simply constructed receivers (11), the holder having a Wahlsc (20) can be set to the reception of the desired sound signal and listened to with headphones. When used in the field of cinema film copy might additionally cause sound tracks with zugeor dneten simultaneous translation of language in addition to the original sound track, these sampled via an adapter at the same time, the transmitter (2) supplied uhrt and from this via the antennas (3 - 6) radiated into the cinema become. Also, the device arrangement in accordance with A / Patent 36 22 32 as a device for reproduction of the subsequent synchronous translation of the language of film prints could be optimally expanded in combina tion with the subject invention. Another application of this invention provide the voice and vocal theater. From the original performance of the piece a female tape is made, which receives the encoded translation operations. Simultaneous band is mehrspurig as embodied and is auft from the master tape which is in synchronism with the performance AVGE, connected by its coding gradually text application to text applications, this circuit are organized according to aufkop FOURTH encoding the prompter by pressing a button before or could also correct. Each track of the tape is therefore associated with a simultaneous limited hours th language whose recording signal by the transmitter (2) via the antennas (3 - 6) and radiated by the receivers (11) is received, depending on the frequency selection who can.