Showing papers on "Sound power published in 2011"

Environmental and Architectural Acoustics

Abstract: Fundamentals of Sound Waves and Hearing. Sound Waves. Speed of Sound. Impetence. Noise and Vibration - Measurement and Rating. Measurement of Sound/Noise. Noise Rating. Measurement of Vibration. Room Acoustics. Sound Field in a Room. Normal Modes of Vibration in Rooms. Reverberation Time. Sound Absorption - Materials and Construction. Types of Sound Absorption Mechanisms. Measurement of Absorption Coefficient and Acoustic Impetence. Characteristics of Porous Sound Absorber. Airborne Sound Insulation. Propagation and Transmission of Airborne Sound. Measurement and Rating of Airborne Sound Insulation. Mass Law for Sound Insulation of a Single Wall. Isolation of Structure-borne Noise and Vibration. Propagation and Radiation of Structure-borne Sound. Reduction of Structure-borne Noise. Measurement and Rating of Impact Sound Insulation. Noise and Vibration Control in the Environment. Basic Strategy. Determination of Required Reduction. Plan for Dealing with Noise and Vibration Sources. Acoustic Design of Rooms. Design Target. Design of Room Shape. Planning the Reverberation. Electro-acoustic systems. Function and Aim of Electro-acoustic Systems. Reinforcement Systems and Architectural Design. Prevention of Howling. Agenda. Wave Equation. Analogues in Electrical, Mechanical and Acoustic Systems and Time Constant. Fourier Transformation and Correlation Functions.

Surround sound system

Abstract: A surround sound system for reproducing a spatial sound field in a sound control region within a room having at least one sound reflective surface. The system uses multiple steerable loudspeakers located about the sound control region, each loudspeaker having a plurality of different individual directional response channels being controlled by respective speaker input signals to generate sound waves emanating from the loudspeaker with a desired overall directional response. A control unit connected drives each of the loudspeakers and has pre-configured filters based on measured acoustic transfer functions for the room for filtering the input spatial audio signals to generate the speaker input signals for all the loudspeakers to generate sound waves with co¬ ordinated overall directional responses that combine together at the sound control region in the form of either direct sound or reflected sound from the reflective surface(s) of the room to reproduce the spatial sound field.

Aeroacoustics of Pipe Systems with Closed Branches

Abstract: Flow induced pulsations in resonant pipe networks with closed branches are considered in this review paper. These pulsations, observed in many technical applications, have been identified as self-sustained aeroacoustic oscillations driven by the instability of the flow along the closed branches. The fundamental aspects of the flow induced pulsations are discussed, with particular attention to the description of the sound sources. A single mode model for the prediction of the self-sustained oscillations is presented, the "energy balance". This model consists of the evaluation of the amplitude of each acoustic mode of the system by means of a balance between the acoustic source power and the acoustic power losses. The main components of this prediction method are discussed; these are the evaluation of the acoustic behavior of a pipe network and the modeling of the sound sources and the acoustic losses. Several field and scale model examples of pipe systems displaying self-sustained oscillations are presented, in order to discuss the parameters influencing the aeroacoustic behavior of pipe networks. Finally some counter-measures for the prevention of self-sustained oscillations are reviewed and perspectives for future work are considered.

Sound reproduction device

Abstract: Provided is a sound reproduction device including a loudspeaker and a superdirective speaker The loudspeaker is configured so that a sound pressure of audible sound produced therefrom decreases as the sound travels farther away from the loudspeaker The superdirective speaker is configured so that a sound pressure of audible sound produced therefrom has a peak at a predetermined distance from the superdirective speaker, and is configured to use an ultrasonic wave as a carrier wave The loudspeaker and the superdirective speaker are positioned such that a loudspeaker sound field of the audible sound produced from the loudspeaker and a superdirective speaker sound field of the audible sound produced from the superdirective speaker overlap with each other at a position of a listener

Assessment of Time-Domain Equivalent Source Method for Acoustic Scattering

Abstract: Equivalent source methods have been developed in the frequency and time domain to provide a fast and efficient computation for acoustic scattering. Although the advantages and capabilities of the method have been demonstrated, the limitations and drawbacks of the method have not yet been explored in detail. A detailed understanding of the equivalent source method is needed to use the method in a wide range of applications with more confidence. This paper presents an assessment of the time-domain equivalent source method for the prediction of acoustic scattering. The sensitivity of the method to numerical parameters, including the number of the surface collocation points, the number and position of the equivalent sources, the time step, and the cut-off singular value, is investigated and suggestions for these parameters are given for accurate predictions. A numerical instability issue is shown and a way to stabilize the solution with a time-averaging scheme is introduced. The sound power is calculated using the equivalent source strength to demonstrate the redistribution of the sound intensity by a scattering body and the conservation of the total power. Finally, scattering of sound from a source in a short duct is tested to demonstrate the utility of the tool for a more complicated shape of the scattering surface.

Topology optimization of composite material plate with respect to sound radiation

Abstract: In this paper, topology optimization of composite material plate with respect to minimization of the sound power radiation has been studied. A new low noise design method based on topology optimization is proposed, which provides great guidance for acoustic designers. The structural vibrations are excited by external harmonic mechanical load with prescribed frequency and amplitude. The sound power is calculated using boundary element method. An extended solid isotropic material with penalization (SIMP) model is introduced for acoustic design sensitivity analysis in topology optimization, where the same penalization is applied for the stiffness and mass of the structural volume elements. Volumetric densities of stiffer material are chosen as design variables. Finally, taking a simple supported thin plate as a simulation example, the sound power radiation from structures subjected to forced vibration can be considerably reduced, leading to a reduction of 20 dB. It is shown that the optimal topology is easy to manufacture at low frequency, while as the loading frequency increases, the optimal topology shows a more and more complicated periodicity which makes it difficult to manufacture.

Comparison of sound power radiation from isolated airfoils and cascades in a turbulent flow

Abstract: An analytical model of the sound power radiated from a flat plate airfoil of infinite span in a 2D turbulent flow is presented. The effects of stagger angle on the radiated sound power are included so that the sound power radiated upstream and downstream relative to the fan axis can be predicted. Closed-form asymptotic expressions, valid at low and high frequencies, are provided for the upstream, downstream, and total sound power. A study of the effects of chord length on the total sound power at all reduced frequencies is presented. Excellent agreement for frequencies above a critical frequency is shown between the fast analytical isolated airfoil model presented in this paper and an existing, computationally demanding, cascade model, in which the unsteady loading of the cascade is computed numerically. Reasonable agreement is also observed at low frequencies for low solidity cascade configurations.

Signatures of Emerging Subsurface Structures in Acoustic Power Maps of the Sun

Abstract: We show that under certain conditions, subsurface structures in the solar interior can alter the average acoustic power observed at the photosphere above them. By using numerical simulations of wave propagation, we show that this effect is large enough for it to be potentially used for detecting emerging active regions before they appear on the surface. In our simulations, simplified subsurface structures are modeled as regions with enhanced or reduced acoustic wave speed. We investigate the dependence of the acoustic power above a subsurface region on the sign, depth, and strength of the wave-speed perturbation. Observations from the Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) prior and during the emergence of NOAA active region 10488 are used to test the use of acoustic power as a potential precursor of the emergence of magnetic flux.

Sound enhancement method, device, program and recording medium

Abstract: A sound enhancement technique that uses transfer functions a i,g of sounds that come from each of one or more positions/directions that are assumed to be sound sources arriving at each microphone to obtain a filter for a position that is a target of sound enhancement, where i denotes a direction and g denotes a distance for identifying each of the positions. Each of the transfer functions a i,g is represented by sum of a transmission characteristic of a direct sound that directly arrives from the position determined by the direction i and the distance g and a transmission characteristic of one or more reflected sounds produced by reflection of the direct sound off an reflective object. A filter that corresponds to the position that is the target of sound enhancement is applied to frequency-domain signals transformed from M picked-up sounds picked up with M microphones to obtain a frequency-domain output signal.

Numerical simulation for prediction of aerodynamic noise characteristics on a HAWT of NREL phase VI

Abstract: The purpose of this study is to numerically predict the characteristics of aerodynamic noise generated from rotating wind turbine blades according to wind speeds using commercial CFD code, FLUENT. The near-field flow around a HAWT of NREL Phase VI is simulated directly by LES, whereas the far-field aerodynamic noise for frequencies below 500 Hz is modeled using FW-H analogy. As there was no experimental noise data, we first compared aerodynamic noise analysis with experimental data. This result showed a difference of power outputs by 0.8% compared with the experimental one with 6.02 kW. Then the characteristics of aerodynamic noise were predicted at a specific location P1 according to IEC 61400-11 international standard. When the wind turbine blades rotate with time, tip-vortices occur at the tip of two blades and are generated periodically in a circle. These vortices in the vicinity of the blade tip cause intense aerodynamic noise due to the tip vortex-trailing edge interaction by local cross flows along the trailing edge. In a wind speed of 7m/s the sound intensity ratio of quadrupole to dipole at P1 location is about 21.1%, but as wind speed increases the sound intensity ratio increases up to 54.3% in the case of no-weighted correction. This means that there is a considerably close relation between the quadrupole noise by small and large scales and the increase of wind speeds. With the purpose of a rough prediction of sound power level, CFD results were compared with a simple model of previous researchers and showed a good agreement with one by Hagg of three other models.

Sound field separation with a double layer velocity transducer array (L)

Abstract: In near-field acoustic holography sound field separation techniques make it possible to distinguish between sound coming from the two sides of the array. This is useful in cases where the sources are not confined to only one side of the array, e.g., in the presence of additional sources or reflections from the other side. This paper examines a separation technique based on measurement of the particle velocity in two closely spaced parallel planes. The purpose of the technique is to recover the particle velocity radiated by a source in the presence of disturbing sound from the opposite side of the array. The technique has been examined and compared with direct velocity based reconstruction, as well as with a technique based on the measurement of the sound pressure and particle velocity. The double layer velocity method circumvents some of the drawbacks of the pressure-velocity based reconstruction, and it can successfully recover the normal velocity radiated by the source, even in the presence of strong disturbing sound.

Mathematically trivial control of sound using a parametric beam focusing source

Abstract: By exploiting a case regarded as trivial, this paper presents global active noise control using a parametric beam focusing source (PBFS). As with a dipole model, one is used for a primary sound source and the other for a control sound source, the control effect for minimizing a total acoustic power depends on the distance between the two. When the distance becomes zero, the total acoustic power becomes null, hence nothing less than a trivial case. Because of the constraints in practice, there exist difficulties in placing a control source close enough to a primary source. However, by projecting a sound beam of a parametric array loudspeaker onto the target sound source (primary source), a virtual sound source may be created on the target sound source, thereby enabling the collocation of the sources. In order to further ensure feasibility of the trivial case, a PBFS is then introduced in an effort to meet the size of the two sources. Reflected sound wave of the PBFS, which is tantamount to the virtual sound source output, aims to suppress the primary sound. Finally, a numerical analysis as well as an experiment is conducted, verifying the validity of the proposed methodology.

Apparatus for generating an enhanced downmix signal, method for generating an enhanced downmix signal and computer program

Abstract: An apparatus for generating an enhanced downmix signal on the basis of a multi-channel microphone signal comprises a spatial analyzer configured to compute a set of spatial cue parameters comprising a direction information describing a direction-of-arrival of a direct sound, a direct sound power information and a diffuse sound power information on the basis of the multi-channel microphone signal. The apparatus also comprises a filter calculator for calculating enhancement filter parameters in dependence on the direction information describing the direction-of-arrival of the direct sound, in dependence on the direct sound power information and in dependence on the diffuse sound power information. The apparatus also comprises a filter for filtering the microphone signal, or a signal derived therefrom, using the enhancement filter parameters, to obtain the enhanced downmix signal.

System and method for an acoustic monitor self-test

Abstract: A system for self-testing an acoustic monitor includes a memory that stores a reference acoustic power of a reference acoustic signal; a digital signal processor (DSP) that computes a real-time acoustic power spectrum of background noise in a frequency range of about 20 Hz to about 80 kHz; a microphone including analog signal conditioning circuitry that receives an acoustic test signal at a test frequency and sound pressure level (SPL), the SPL including an attenuation level; and a processor that compares a measured acoustic power at the test frequency with a calculated acoustic power of the acoustic test signal, the calculated acoustic power including the reference acoustic power and the attenuation level; where the acoustic monitor includes the DSP in signal communication with the microphone.

Newly identified properties of surface acoustic power

Abstract: The cause of enhanced acoustic power surrounding active regions, known as the acoustic halo, is not as yet understood. We explore the properties of the enhanced acoustic power observed near disk center from 21 to 27 January 2002, including AR 9787. We find that i) there exists a strong correlation of the enhanced high-frequency power with magnetic-field inclination, with greater power in more horizontal fields, ii) the frequency of the maximum enhancement increases along with magnetic-field strength, and iii) the oscillations contributing to the halos show modal ridges that are shifted to higher wavenumber at constant frequency in comparison to the ridges of modes in the quiet Sun.

Sound source separation device, sound source separation method and program

Abstract: With conventional source separator devices, specific frequency bands are significantly reduced in environments where dispersed static is present that does not come from a particular direction, and as a result, the dispersed static may be filtered irregularly without regard to sound source separation results, giving rise to musical noise. In an embodiment of the present invention, by computing weighting coefficients which are in a complex conjugate relation, for post-spectrum analysis output signals from microphones ( 10, 11 ), a beam former unit ( 3 ) of a sound source separator device ( 1 ) thus carries out a beam former process for attenuating each sound source signal that comes from a region wherein the general direction of a target sound source is included and a region opposite to said region, in a plane that intersects a line segment that joins the two microphones ( 10, 11 ). A weighting coefficient computation unit ( 50 ) computes a weighting coefficient on the basis of the difference between power spectrum information calculated by power calculation units ( 40, 41 ).

Technical Possibilities of Reducing the Sound Pressure Level Emitted into the Environment by a Power Transformer

Abstract: The subject presented in this paper refers to measurements and assessment of the corrected sound pressure level values (noise) occurring around a medium-power transformer. The paper presents the values of noise accompanying the operation of the power object before and after its modernization, which consisted in repeated core pressing and replacement of the cooling system. The main aim of the research work was the assessment of the influence of the repair work on the noise level emitted into the environment.

Sound source separator device, sound source separator method, and program

Abstract: With conventional source separator devices, specific frequency bands are significantly reduced in environments where dispersed static is present that does not come from a particular direction, and as a result, the dispersed static may be filtered irregularly without regard to sound source separation results, giving rise to musical noise. In an embodiment of the present invention, by computing weighting coefficients which are in a complex conjugate relation, for post-spectrum analysis output signals from microphones (10, 11), a beam former unit (3) of a sound source separator device (1) thus carries out a beam former process for attenuating each sound source signal that comes from a region wherein the general direction of a target sound source is included and a region opposite to said region, in a plane that intersects a line segment that joins the two microphones (10, 11). A weighting coefficient computation unit (50) computes a weighting coefficient on the basis of the difference between power spectrum information calculated by power calculation units (40, 41).

Acoustic transducer device

Abstract: The present invention relates to a sound converter, and, more particularly, to a sound converter which can solve a problem in that a vibration space decreases in the sound converter requiring high outputs, as the overall height of a voice coil increases.

Acoustical power amplification and damping by temperature gradients

Abstract: Ceperley proposed a concept of a traveling wave heat engine [“A pistonless Stirling engine—The traveling wave heat engine,” J. Acoust. Soc. Am. 66, 1508–1513 (1979).] that provided a starting point of thermoacoustics today. This paper verifies experimentally his idea through observation of amplification and strong damping of a plane acoustic traveling wave as it passes through axial temperature gradients. The acoustic power gain is shown to obey a universal curve specified by a dimensionless parameter ωτα; ω is the angular frequency and τα is the relaxation time for the gas to thermally equilibrate with channel walls. As an application of his idea, a three-stage acoustic power amplifier is developed, which attains the gain up to 10 with a moderate temperature ratio of 2.3.

Wading detection system for a vehicle

Abstract: A wading indicator system for a vehicle comprising: at least one sound wave pulse emitter device; at least one sound wave pulse receiver device; and a control unit. The control unit configured to measure one or more of the following variables: (i) the time of flight of a sound pulse between the at least one sound wave pulse emitter device and the at least one sound wave pulse receiver device; (ii) the amplitude of a sound pulse emitted by the at least one sound wave pulse emitter device when received by the at least one sound wave pulse receiver device; and (iii) the wavelength of a sound pulse emitted by the at least one sound wave pulse emitter device when received by the at least one sound wave pulse receiver device. Thereby the control unit is configured to determine whether at least a portion of the vehicle is immersed in water.

Method and apparatus for simultaneously controlling near sound field and far sound field

Abstract: An apparatus and method for forming a Personal Sound Zone (PSZ) at a location of a listener are provided. An apparatus for simultaneously controlling a near sound field and a far sound field may classify the near sound field and the far sound field based on a distance between an array speaker and a listener, and may control the near sound field and the far sound field and thus, it is possible to perform focusing even when the listener is located in adjacent to the array speaker. Additionally, the apparatus may generate a directive sound source using the array speaker, and at the same time, may reduce a sound pressure in a far field, thereby reducing a sound source spreading to the far field while focusing is performed at the location of the listener.