Showing papers on "Sound power published in 2001"

A method of improving the audibility of sound from a loudspeaker located close to an ear

Abstract: A method of improving the audibility of sound from a loudspeaker (1) located close to an ear (2) comprises detecting ambient sounds arriving from other sound sources using a transducer (3) which provides corresponding ambient sound signals, inverting the polarity of said signals, and passing the said ambient sound signals through a filter (4) having a transfer function which compensates for the spectral acoustic modification of sounds travelling from the loudspeaker to the ear caused by the proximity of the ear to the loudspeaker, and/or the proximity of the transducer to the head, and combining the filtered ambient sound signals with the signals being fed to the loudspeaker to reduce the audibility of said ambient sounds.

Electromagnetic vibration and noise assessment for surface mounted PM machines

Abstract: Analysis of electromagnetic vibration and acoustic noise assessment and methods to minimize resultant sound power level for low noise motor design is presented in this paper. The linear model of the exciting force wave is derived to evaluate the exciting force and to optimize the design of stator winding, rotor PM shape and rotor PM skew angle for minimization of sound power level for low noise motor design. Mode number and frequency of the exciting force wave, natural vibration frequency, maximum vibration velocity and maximum vibration displacement of main vibration source are introduced to evaluate machine vibration. Resultant sound power levels for the cylindrical sound wave and the plane sound wave models are introduced to analyze the acoustic noise assessment of both axial and radial flux PM machines respectively. Finally, electromagnetic vibration and acoustic noise assessment of both radial and axial flux surface mounted motor structures are completed and illustrated in the paper.

Temporal Integration of Sound Pressure Determines Thresholds of Auditory-Nerve Fibers

Abstract: Current propositions of the quantity of sound driving the central auditory system, specifically around threshold, are diverse and at variance with one another. They include sound pressure, sound power, or intensity, which are proportional to the square of pressure, and energy, i.e., the integral of sound power over time. Here we show that the relevant sound quantity and the nature of the threshold can be obtained from the timing of the first spike of auditory-nerve (AN) fibers after the onset of a stimulus. We reason that the first spike is triggered when the stimulus reaches threshold and occurs with fixed delay thereafter. By probing cat AN fibers with characteristic frequency tones of different sound pressure levels and rise times, we show that the differences in relative timing of the first spike (including latencies >100 msec of fibers with low spontaneous rates) can be well accounted for by essentially linear integration of pressure over time. The inclusion of a constant pressure loss or gain to the integrator improves the fit of the model and also accounts for most of the variation of spontaneous rates across fibers. In addition, there are tight correlations among delay, threshold, and spontaneous rate. First-spike timing cannot be explained by models based on a fixed pressure threshold, a fixed power or intensity threshold, or an energy threshold. This suggests that AN fiber thresholds are best measured in units of pressure by time. Possible mechanisms of pressure integration by the inner hair cell–AN fiber complex are discussed.

Experimental Study and Simulation of Rocket Engine Freejet Noise

Abstract: On behalf of CNES and in the framework of studies concerning the acoustic environment of Ariane 5 launcher at lift-off, ONERA has adapted to the near sound field simulation a NASA's jet noise model of the 1970's. In order to validate this model, tests have been carried out with static rockets of various sizes. Several improvements appear to be necessary for a precise simulation of the acoustic measurements: in particular, the characteristic length of the model must be reduced and the fully expanded jet data must be used instead of the jet exhaust data. It is shown that the acoustic efficiency, for a given Mach number, is not dependent on the rocket size, and may be estimated from a semi-empirical formula found in the literature. The model changes are checked with other jets of various characteristics. On the basis of experiments and following an approach deduced from an earlier study, the spatial characteristics of the sound field and more particularly the sound power peak location are related to the supersonic length of the flow, which appears to be the adequate reference length for a future jet noise model.

Sound source probing system

Abstract: In order to specify and display the source of noise in a factory, or the like, accurately even in the outdoors, two pairs of microphones (M1, M3; M2, M4) are disposed, respectively, on the X axis and Y axis while spaced apart by a distance L. Direction of a sound source is estimated based on the difference of arriving time of output signals from the pair of microphones (M1, M3) and the difference of arriving time of output signals from the pair of microphones (M2, M4). Furthermore, the image in the vicinity of an estimated sound source is picked up by means of a camera (11) and the estimated position of sound source is indicated on an image displayed on the display (23) of a personal computer (20).

Active vibroacoustic control with multiple local feedback loops

Abstract: The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed under each sensor. With ideal force actuators, the plant response is passive for such an arrangement of collocated actuator/sensor pairs and so decentralized (local) feedback is guaranteed stable. This property is shown to extend to collocated velocity sensors and piezoceramic actuators over the bandwidth of interest and so multiple local feedback loops are also predicted to be stable. The performance of such a system is simulated in controlling the vibration and sound transmission through a thin plate, excited by an acoustic plane wave, with a 4 x 4 array of such actuator/sensor pairs, which are connected together with 16 local feedback control loops. Using force actuators, significant frequency-averaged reductions up to 1kHz in both the kinetic energy (28dB) and transmitted sound power (18dB) can be obtained with an appropriate feedback gain in each loop. These reductions are not so great with piezoelectric actuators (12dB and 9dB respectively) but their use allows the controller to be fully integrated in the structure.

Turbine blade/vane interaction noise: acoustic mode analysis using in-duct sensor rakes

Abstract: The sound field in the outlet duct of a high speed low-pressure turbine was studied to deepen the understanding of the sound generating mechanisms in a three-stage turbine. Special interest was given to the influence of the exit guide vanes (EGV) downstream of the turbine on the noise generation. Six radial rakes carrying ten Kulite-sensor probes each were mounted downstream of the EGVs in the cylindrical duct section of the turbine exit. The rakes were positioned at different azimuthal angles and staggered axially in pairs to avoid probe wake interference. The rakes were traversed azimuthally over 180 degrees in steps of 1.5 degrees to give a total of 240x30 measurement points. All sensor signals were acquired simultaneously with a sampling frequency of 22 kHz and stored digitally for later analysis in the frequency range 0-8.5 kHz. Measurements were made at operating conditions from 63% to 99% rotor design speed. Special attention was given to the blade passing frequencies (BPF) of the three turbine rotors. The chosen experimental setup permits decomposition of the sound field into azimuthal and radial modes. With this information, the sound power transmitted upstream as well as downstream can be calculated for frequencies up to 6 kHz. The results of the mode analysis provide a detailed view on the sound generation mechanisms and interaction processes between the various blade and vane rows. According to Tyler & Sofrin, the noise sources can be separated in rotor/statorand rotor/stator/EGV-interactions with associated azimuthal modes.

Fluid density measurement using acoustic pressures for industrial sensing applications

Abstract: The density of at least one fluid in a pipe 12 is determined using a pair of effective sound speeds a 1eff and a 2eff of the fluid/pipe system. The pair of effective system sound speed measurements are taken at two sensing regions X 1 , X 2 along the pipe wherein each of the sensing regions comprises a different system cross sectional compliance. The pair of effective system sound speeds a 1eff and a 2eff are provided to signal processing logic 60, which determines the density of the fluid 13 flowing in the pipe 12. The effective system sound speeds a 1eff and a 2eff may be provided by a pair of sound speed meters positioned at sensing regions X 1 , X 2 wherein the sound speed meters utilize a spatial array of acoustic pressure sensors placed at predetermined axial locations along the pipe 12. The acoustic pressure sensors provide acoustic pressure signals which are utilized to determine the effective system speed of sound a 1eff and a 2eff of the fluid (or mixture)/pipe system. One technique uses acoustic spatial array signal processing techniques with the direction of propagation of the acoustic signals along the longitudinal axis of the pipe 12. However, numerous spatial array-processing techniques may be employed to determine the effective system speed of sounds a 1eff and a 2eff . The effective system sound speeds a 1eff and a 2eff measured utilize one-dimensional planar acoustic waves that are lower in frequency (and longer wavelength) signals than those used for ultrasonic flow meters, and thus incorporates pipe compliance with fluid compliance and further is more tolerant to inhomogeneities in the flow. In addition, no external source is required and thus may operate using passive listening. The invention will work with arbitrary sound speed meter spacing and with as few as two sound speed meters. The density meter may also be combined with an instrument, an opto-electronic converter and a controller in an industrial process control system.

Active Control of the Flow-Induced Noise Transmitted Through a Panel

Abstract: Active control of sound transmitted through an elastic panel when excited by a turbulent boundary layer is investigated. The motivation is the control within an aircraft cabin of the flow-induced noise due to the wall-pressure fluctuations over the fuselage. The excitation is random and so the plate velocity and the radiated sound pressure must be described by spectral densities. These quantities can be obtained from an analysis of the response of the system to a harmonic deterministic excitation and a statistical model for the turbulent boundary layer. Criteria are discussed under which the cross-modal coupling of the structural modes can be neglected when excited by a turbulent boundary layer. When considering subsonic turbulent flows, parametric studies show that each structural mode radiates sound independently. Hence, a suitable strategy for the active structural acoustic control of the sound power transmitted through the panel would be independent feedback control of each structural mode of the system in the low-frequency domain. The performance of this active control strategy is compared to that obtained by controlling the radiation modes of the panel for different numbers of control channels.

Electroacoustic waveguide transducing

Abstract: An acoustic waveguide system, having source of acoustic radiation and a source of opposing acoustic radiation. An acoustic waveguide has an open end and an interior. A first acoustic driver having a first radiating surface and a second radiating surface is arranged and constructed so that the first radiating surface radiates sound waves into free air and the second radiating surface radiates sound waves into the acoustic waveguide so that sound waves are radiated at the open end. A source of opposing sound waves in the acoustic waveguide opposes a predetermined spectral component of the sound waves radiated into the acoustic waveguide to reduce the acoustic radiation of the predetermined spectral component from the acoustic waveguide.

Road surface determination device and system

Abstract: PROBLEM TO BE SOLVED: To precisely detect a road surface condition with a practical sampling frequency. SOLUTION: An acceleration sensor 10 and a sound pressure sensor 12 are arranged inside a tire. A waveform comparison circuit 18E determines a road surface according to an acceleration reference waveform and a waveform of an acceleration signal. A waveform comparison circuit 20E determines the road surface according to a sound pressure reference waveform and a waveform of a sound pressure signal. A power spectrum comparison circuit 18F determines the road surface according to comparison between an acceleration reference power spectrum and an acceleration power spectrum obtained from the acceleration signal. A power spectrum comparison circuit 20F determines the road surface according to comparison between a sound pressure reference power spectrum and a sound power spectrum obtained from the sound pressure signal. A road surface determination circuit 22 determines the road surface according to a majority of the surface determination results. COPYRIGHT: (C)2003,JPO

Apparatus and method for generating additional sound on the basis of sound signal

Abstract: Sound signal indicative of a human voice or musical tone is input, and the pitch of the input sound signal is detected. Then, a scale note pitch is determined which is nearest to the detected pitch of the input sound signal. In the meantime, a scale note pitch of an additional sound or harmony sound to be added to the input sound is specified in accordance with a harmony mode selected by a user. The scale note pitch of the additional sound to be generated is modified in accordance with a difference between the determined scale note pitch and the detected pitch of the input sound signal. Because the additional sound is generated with the modified pitch, it can appropriately follow a variation in the pitch of the input sound to be in harmony with the input sound, rather than exactly agreeing with the scale note pitch. As another example, reference scale note pitch data may be supplied, instead of the scale note pitch nearest to the detected pitch of the input sound signal being determined in the above-mentioned manner.

Vibration excited sound absorber

Abstract: A vibration excited sound absorber (2) for reducing the sound radiation from a vibrating surface (3). Each sound absorber (2) has a radiating element (4) which is connected to the vibrating surface (3) by a coupling means (30). The vibrating surface (3) is partially covered with one or more devices. The dynamic response of the sound absorber (2) is tuned so that the volume velocity of the radiating element (4) is substantially equal in amplitude but opposite in phase relative to the volume velocity of the surrounding exposed vibrating surface (3). The net volume velocity of the surface is thereby reduced.

System for integrating mid-range and high-frequency acoustic sources in multi-way loudspeakers

Abstract: This invention provides a radiation boundary integrator (“RBI”) for integrating sound radiation from mid-range and high-frequency sources in multi-way loudspeakers. The RBI is a substantially solid boundary that is placed over the mid-range speakers to provide smooth, wave-guiding side walls to control the angular radiation of the high-frequency sound waves emanating from the high-frequency sound sources. To allow the mid-range frequency sound waves generated from mid-range sound sources to pass through the RBI, the RBI is designed with openings. To further prevent the possibility of having high-frequency sound radiate through the openings in the RBI, the RBI may be designed with porous material in the openings of the RBI. The porous material would be transparent to the mid-range sound radiation, but would prevent the high-frequency sound radiation from being disturbed by the openings in the RBI. As such, the RBI provides an outer or front surface area that forms an acoustical barrier to high frequencies radiating across the front surface, yet is acoustically transparent to mid-range frequencies radiating through openings in the RBI. The RBI may also serve as a volume displacement device to compression-load the mid-range sound sources by contouring the back side of the RBI to the shape of the mid-range sound sources thus reducing the space between the RBI and the mid-range sound sources and loading the mid-range sound sources to generate greater mid-range sound energy.

Sonic water level measuring method and system there for

Abstract: A sonic water level measuring method and system for mounting a wave-guide tube for measuring a water level in a reservoir, a river, etc. generating sonic pulses at the upper of the wave-guide tube, measuring transit times that it takes for the sonic pulses to transit from an original point to a water surface through air medium and transit back to the original point after being reflected on the water surface and multiplying the transit times by a sound velocity to compute a water level is configured to measure the sound velocity using the times that it takes for the sonic pulse to transit in two intervals in order to exactly measure the sound velocity that is changed according to the changing of an air temperature, pressure and component in the wave-guide tube and then measure the water level considering an arithmetical average value of the sound velocities measured as a sound velocity in the wave-guide tube.

Active control of fan tone noise from aircraft engines

Abstract: The noise reduction potential of different active noise control (ANC) configurations and control algorithms for the application to aircraft engines were studied. The work was done within the framework of the Brite/Euram research project RANNTAC (Reduction of Aircraft Noise by Nacelle Treatment and Active Control). ANC was applied to a fan model of 0.47m-diamete r in the SNECMA test facility in Villaroche, France. Loudspeakers mounted flush with the inner wall of the inlet duct were used as secondary acoustic sources. CNRS and EADS implemented various algorithms for active control using microphones as error sensors which are mounted (1) in the inlet duct and (2) in the free field upstream of the fan intake. DLR performed an acoustic mode analysis of the sound field in the inlet duct for the cases with and without ANC. For this purpose DLR designed and constructed a special duct section with 96 ports for wall-flush mounting of precision microphones and developed an appropriate analysis technique. Decomposition of the sound field into azimuthal and radial mode components provided detailed information on the effectiveness of the various active noise control techniques used. The sound power reductions achieved with ANC in the upstream far field were documented by microphoneantenna measurements conducted by SNECMA and served for further validation of the experimental findings.

Picked-up-sound recording method and apparatus

Abstract: Sound picked up by a microphone of a first sound field is reproduced by a speaker of a second sound field, and a sound picked up by a microphone of the second sound field is reproduced by the speaker of the first sound field. Sound pressure detection section detects a sound pressure of a sound present in the second (or first) sound field picked up by the microphone of the second (or first) sound field, other than a sound reproduced by the speaker of the first (or second) sound field. Other sound pressure detection section detects a sound pressure with which the sound picked up by the microphone of the second (or first) sound field and reproduced by the speaker of the first (or second) sound field is picked up by the microphone of the first (or second) sound field. Sound-pressure-difference detection section adjusts a gain of an automatic gain adjustment section in such a manner that the two detected sound pressures assume a predetermined relationship. Thus, any sound picked up in one of the first and second sound fields can be reproduced in the other sound field with an enhanced sense of unity and connection between the two sound fields.

Acoustic power flux in a waveguide

Abstract: The acoustic power flux that occurs in an ideal waveguide in the presence of two modes propagating in it is considered. Singular points of the saddle and vortex types are found for modes of different numbers. The regions lying near the vortex-type points and characterized by the inverse direction of the power flux (i.e., from the receiver to the source) are determined. When a low-number mode propagates together with a higher-number one, the regions, where the power flux noticeably deviates from the general propagation direction, occupy a considerable part of the longitudinal section area of the waveguide.

A new approach to the measurement of transverse vibration and acoustic radiation of automotive belts using laser Doppler vibrometry and acoustic intensity techniques

Abstract: This work aims at utilizing state-of-the-art and powerful measurement techniques to develop a tool for estimating the acoustic radiation of synchronous belts during the design stage. One of the main objects of this work is that of reducing the large number of tests currently employed. Effective measurement technologies, such as laser and acoustic intensity measurement techniques, are employed to support the entire development of the predicting tool, from the analysis of the noise and vibration phenomena to the validation of the numerical models. The proposed method can also be applied successfully to the analysis of noise generating mechanisms, especially belt vibration responses. In a previous work, it has been shown that the noise radiated at meshing frequency by a belt drive, simply composed of two pulleys and driven by an electric motor, can be estimated using vibration measurements, taken by a scanning laser Doppler vibrometer, as inputs for a boundary element model. The same approach is here extended to a more complex test bench, with an internal combustion engine cylinder head giving additional excitation. The test bench has been designed and realized in order to reduce the noise radiation due to interfering sources (electric motor, cooling system etc) and to make it possible to measure the noise contribution from the belt drive only. Reference noise measurements have been performed by acoustic intensity techniques. The sound power values obtained from these measurements have been compared to those obtained from the boundary element model. The techniques employed in this work have been shown to be able to analyse resonance and meshing phenomena on a real belt drive geometry, as had not been done before, based on the literature survey reported.

Fluid density measurement in pipes using acoustic pressures

Abstract: The density of at least one fluid in a pipe is determined using a pair of effective sound speeds a 1eff and a 2eff of the fluid/pipe system. The pair of effective sound speed measurements is taken at two sensing regions along the pipe wherein each of the sensing regions has a different cross sectional area compliance. The pair of effective sound speeds a 1eff and a 2eff is provided to signal processing logic 60, which determines the density of the fluid flowing in the pipe. The effective sound speeds a 1eff and a 2eff may be provided by a pair of sound speed meters positioned at the sensing regions wherein the sound speed meters utilize a spatial array of acoustic pressure sensors placed at predetermined axial locations along the pipe. The acoustic pressure sensors measure one-dimensional planar acoustic waves that are lower in frequency (and longer wavelength) signals than those used for ultrasonic flow meters, and thus is more tolerant to inhomogeneities in the flow. In addition, no external acoustic source is required and the meters may operate using passive listening.

Sound fields in a rectangular enclosure under active sound transmission control

Abstract: The present study evaluates the effectiveness of active sound transmission control inside an enclosure using a purely acoustic source under the potential energy, squared pressure, and energy density control algorithms. Full coupling between a flexible boundary wall and the interior acoustic cavity is considered. Formulas based on the impedance-mobility approach are developed for the active control of sound transmission with the energy density control algorithm. The resultant total acoustic potential energy attenuation and sound fields under the three control algorithms are compared. Global amplification of the sound level with localized quiet zones under the squared pressure control is observed. This adverse effect can be removed by using the energy density control. It is also shown that the energy density control provides a more uniform control of sound field. Better performance of global and local control of sound field using the squared pressure and energy density controls can be achieved by locating the error sensors at the peak quiet zones and the areas of peak energy density attenuation, respectively, obtained under potential energy control.

Actively-controlled sound absorption panel system using movement-controlled reflective plate

Abstract: A space 4 constituted by a sound absorption panel section 1 and active sound absorption control system section 2 between the inner and outer walls of a nacelle forming an engine intake/exhaust duct is utilized as an acoustic resonance field and as a sound absorption field by sticking a porous sound absorption material 14 onto the inside wall surface of the space. The panel section 1 defines a sound absorption space by means of surface plate 6 made of a perforated plate and wire mesh materials plate, panel construction side plate 9 and back sheet plate 13 having porous sound absorption material stuck thereon; and a movement-controlled reflective plate 8, that is capable of movement/rotation control with respect to said perforated plate, is provided within this sound absorption space. Movement of the reflective plate 8 is controlled utilizing the adaptive feed forward control method by means of the output from an active sound absorption control system section 2; thus fan noise and/or turbine noise emitted from a turbofan engine I.E. engine noise over a wide frequency range from low-frequency noise to higher harmonics of fan blade passing frequency tone is actively reduced in a manner responsive to changes of engine noise source character.

Picked-up-sound reproducing method and apparatus

Abstract: Sound picked up by a microphone of a first sound field is reproduced by a speaker of a second sound field, and a sound picked up by a microphone of the second sound field is reproduced by the speaker of the first sound field. Sound pressure detection section detects a sound pressure of a sound present in the second (or first) sound field picked up by the microphone of the second (or first) sound field, other than a sound reproduced by the speaker of the first (or second) sound field. Other sound pressure detection section detects a sound pressure with which the sound picked up by the microphone of the second (or first) sound field and reproduced by the speaker of the first (or second) sound field is picked up by the microphone of the first (or second) sound field. Sound-pressure-difference detection section adjusts a gain of an automatic gain adjustment section in such a manner that the two detected sound pressures assume a predetermined relationship. Thus, any sound picked up in one of the first and second sound fields can be reproduced in the other sound field with an enhanced sense of unity and connection between the two sound fields.