Showing papers on "Sound power published in 1993"

Radiation modes and the active control of sound power

Abstract: Two formulations for calculating the total acoustic power radiated by a structure are compared; in terms of the amplitudes of the structural modes and in terms of the velocities of an array of elemental radiators on the surface of the structure. In both cases, the sound radiation due to the vibration of one structural mode or element is dependent on the vibration of other structural modes or elements. Either of these formulations can be used to describe the sound power radiation in terms of a set of velocity distributions on the structure whose sound power radiation is independent of the amplitudes of the other velocity distributions. These velocity distributions are termed ‘‘radiation modes.’’ Examples of the shapes and radiation efficiencies of these radiation modes are discussed in the cases of a baffled beam and a baffled panel. The implications of this formulation for the active control of sound radiation from structures are discussed. In particular, the radiation mode formulation can be used to provide an estimate of the number of independent parameters of the structural response which need to be measured and controlled to give a required attenuation of the radiated sound power.

Stereo headphone sound source localization system

Abstract: A system for processing an audio signal for playback over headphones in which the apparent sound source is located outside of the head of the listener processes the input signal as if it were made up of a direct wave portion, an early reflections portion, and a reverberations portion. The direct wave portion of the signal is processed in filters whose filter coefficients are chosen based upon the desired azimuth of the virtual sound source location. The early reflection portion is passed through a bank of filters connected in parallel whose coefficients are chosen based on each reflection azimuth. The outputs of these filters are passed through scalars to adjust the amplitude to simulate a desired range of the virtual sound source. The reverberation portion is processed without any sound source location information, using a random number generator, for example, and the output is attenuated in an exponential attenuator to be faded out. The outputs of the scalars and attenuators are then all summed to produce left and right headphone signals for playback over the respective headphone transducers.

On feedforward active control of sound and vibration using vibration error signals

Abstract: The problem of sensing structural vibration to provide an error signal for vibration source‐based adaptive feedforward control systems implemented to attenuate globally both structural and acoustic disturbances is considered. It is shown that designing a control system that simply aims to minimize structural vibration is not necessarily the best approach, particularly in structural/acoustic problems. Rather, by considering the governing equation of the global error criterion of interest it is possible to derive orthogonal groups of structural modes that contribute to the error criterion as a set. It is these orthogonal groupings that should be sensed as an error signal by an adaptive feedforward control system (and minimized in amplitude), a task that could be accomplished using shaped piezoelectric polymer film sensors or discrete measurement/modal filtering techniques. Specific examples relating to the minimization of radiated acoustic power and acoustic potential energy in a coupled enclosure are given...

The energetic costs of calling in the bushcricket requena verticalis (orthoptera: tettigoniidae: listroscelidinae)

Abstract: 1. The metabolic costs of calling for male Requena verticalis Walker (Tettigoniidae: Listroscelidinae) were measured by direct recordings of oxygen consumption. The acoustic power output was measured by sound pressure levels around the calling bushcricket. 2. The average metabolic cost of calling was 0.143 ml g-1 h-1 but depended on calling rate. The net metabolic cost of calling per unit call, the syllable, was calculated to be 4.34×10-6+/−8.3×10-7 ml O2 syllable-1 g-1 body mass (s.e.) from the slope of the relationship between total V(dot)O2 and rate of syllable production. The resting V(dot)O2, calculated as the intercept of the relationship, was 0.248 ml O2 g-1 body mass h-1. 3. The energetic cost of calling for R. verticalis (average mass 0.37 g) was estimated at 31.85×10-6 J syllable-1. 4. Sound pressure levels were measured around calling insects. The surface area of a sphere of uniform sound pressure level [83 dB SPL root mean square (RMS) acoustic power] obtained by these measurements was used to calculate acoustic power. This was 0.20 mW. 5. The metabolic efficiency of calling, based on total metabolic energy utilisation, was 6.4 %. However, we propose that the mechanical efficiency for acoustic transmission is closer to 57 %, since only about 10 % of muscle metabolic energy is apparently available for sound production. 6. R. verticalis emits chirps formed of several syllables within which are discrete sound pulses. Wing stroke rates, when the insect is calling at its maximal rate, were approximately 583 min-1. This is slow compared to the rates observed in conehead tettigoniids, the only other group of bushcrickets where metabolic costs have been measured. The thoracic temperatures of males that had been calling for 5 min were not significantly different from those of non-calling males. 7. For R. verticalis, calling with relatively slow syllable rates may reduce the total cost of calling, and this may be a compensatory mechanism for their other high energetic cost of mating (a large spermatophylax).

Acoustic power calibrations of cylindrical intracavitary ultrasound hyperthermia applicators

Abstract: Preliminary clinical results indicate that some tumors can be heated well utilizing cylindrical ultrasound sources placed in body cavities. In this paper a simple method for measuring the acoustic power from cylindrical intracavitary transducers will be described. The radially propagating acoustic field was converted to a beam with a single propagation direction by a brass reflector, and the radiation force generated by this beam on an absorbing target was measured. The power output of several clinical intracavitary arrays varied significantly between identically shaped transducer elements. The results show that it is important to measure the acoustic power output from each element prior to its clinical use. The radiation force technique is simple and sensitive and can be easily adapted to be used as a routine clinical quality assurance method.

Sound environment simulator using a computer simulation and a method of analyzing a sound space

Abstract: The present invention discloses a sound environment simulator including a sound field analyzing unit, a sound field reproducing unit, and an output unit. The sound environment analyzing unit divides the solid surfaces of a space to be analyzed into a set of sections to compute the volume of reflected sounds with a sound absorption coefficient of walls and form factors. It further computes time series data related to the arrival volume of sounds emanated from a certain sound source to the sound receiving point. An impulse response computing unit in the sound field reproducing unit transduces the time series data into an impulse response. Accordingly, the sound field reproducing unit convolutes the impulse response on a dry source in accordance with data related to a listener's position inputted from an associated virtual reality equipment to generate a reproduced sound over a headphone.

Acoustic radiation from a thin airfoil in nonuniform subsonic flows

Abstract: Noise resulting from the interaction of a three dimensional gust is modeled directly from unsteady aerodynamic codes. This paper provides bench mark results for the case of a thin airfoil for comparison with the more complex case of a loaded airfoil. It is shown that the acoustic pressure pattern strongly depends on the value of a certain reduced frequency. The effects of an oblique gust are examined and shown to significantly reduce the acoustic power for certain gust parameters range. The Acoustic power versus the gust frequency exhibits a maximum. High frequency and non-compact source effects are also investigated.

Computation of the sound generated by isotropic turbulence

Abstract: The acoustic radiation from isotropic turbulence is computed numerically. A hybrid direct numerical simulation approach which combines direct numerical simulation (DNS) of the turbulent flow with the Lighthill acoustic analogy is utilized. It is demonstrated that the hybrid DNS method is a feasible approach to the computation of sound generated by turbulent flows. The acoustic efficiency in the simulation of isotropic turbulence appears to be substantially less than that in subsonic jet experiments. The dominant frequency of the computed acoustic pressure is found to be somewhat larger than the dominant frequency of the energy-containing scales of motion. The acoustic power in the simulations is proportional to epsilon (M(sub t))(exp 5) where epsilon is the turbulent dissipation rate and M(sub t) is the turbulent Mach number. This is in agreement with the analytical result of Proudman (1952), but the constant of proportionality is smaller than the analytical result. Two different methods of computing the acoustic power from the DNS data bases yielded consistent results.

Active control of sound power using acoustic basis functions as surface velocity filters

Abstract: An improved method of active structural acoustics control is presented that is based on the minimization of the total power radiated from any structure expressed in terms of a truncated series sum. Each term of this sum is related to the coupling between the orthogonal eigenvectors of the radiation impedance matrix (referred to as ‘‘basis functions’’ in this paper) and the structural surface velocity vector. The basis functions act as surface velocity filters. These acoustic basis functions are found to be weak functions of frequency but their corresponding weighting coefficients increase monotonically with frequency. The minimization of the radiated power is shown to result in a structural surface velocity vector that couples poorly to those acoustic basis functions that account for high‐efficiency sound radiation. This strategy is demonstrated numerically for a clamped–clamped baffled beam in air. Point force primary and control actuators (shakers) are used to explore the control mechanisms. As expected...

Acoustic output device, and electronic apparatus using the acoustic output device

Abstract: Sound waves from a plate-shaped acoustic source, which generates fundamental waves (sound waves) having at least two frequencies, propagate through a propagating portion. The propagating portion consists of a medium in which a non-linear interaction is induced by the fundamental waves. A secondary sound wave having a frequency conforming to the difference between the two fundamental waves is generated by the medium. Fundamental wave components other than the secondary sound wave are absorbed by an acoustic absorber so that only the secondary sound wave is delivered as an output. The acoustic source, propagating portion and acoustic absorber are substantially transparent and stacked in three layers. This allows the resulting acoustic output device to be incorporated in the display unit of an electronic apparatus.

Intake sound control apparatus

Abstract: A device for cancelling annoying sounds caused by operation of an internal combustion engine. An intake sound of the engine, and also a rotational speed of the engine, are obtained. The phase difference between the present intake sound and a desired intake sound is obtained using map data. The map data depends on the rotational speed of the engine and is specifically calculated so that at least the (n+0.5) harmonics (n integer≧0) are cancelled. The phase data is used to drive a ceramic speaker or two oppositely directed ceramic speakers, to appropriately compensate the input sound.

Sound constituting apparatus

Abstract: A sound constituting apparatus translates a sensor output, as detected by an input detection unit, such as state changes, into electrical signals. A data extracting unit makes use of these electrical signals as an information concerning an external environment to extract the results of analyses of the information concerning the external environment as data. A sound source controlling unit outputs sound source controlling data, based on the data extracted by the data extracting unit, and translates the output signals into a modified sound by a sound producing device to eliminate time constraint. In producing the sound, at least one of physical parameters, namely the noise of the external environment, vibrations, light, temperature, humidity or atmospheric pressure, time parameters such as time, day and season and biological information parameters, such as brain waves, body temperature, pulsation, perspiration, number of breaths, is selected to detect the state or changes in the state in such external environment or living body for conversion into electrical signals. The apparatus then fetches the information concerning the external environment to translate it instantly into an output sound totally different from the original sound. In this manner, a sound totally different from the original sound is produced and outputted without employing complex theories.

Sound reproduction system.

Abstract: The invention relates to a sound reproduction system comprising a source of a sound signal in electrical form, a first filter group (13) for dividing the signal derived from the sound signal source into several sound signals occurring in different frequency bands and an adjustable gain amplifier (2) for each frequency band for amplifying the sound signal occurring in said frequency band. To take into account the noise existing in the environment of the sound reproduction system in the adjustment of the system, the system further comprises means (3) for generating an electrical signal proportional to the background noise existing in the environment and means (CS1...CSN) for adjusting the gain of the amplifiers in response to said electrical signal proportional to the background noise.

Structural and Acoustic Noise Produced by Turbulent Flow over an Elastic Trailing Edge

Abstract: An analysis is made of the sound and vibration produced by turbulent flow at low Mach number over the trailing edge of an elastic plate. The trailing edges of airfoils and other flow control surfaces are known to be important sources of high frequency sound. When the surface is compliant the turbulent edge-flow also excites structural modes of vibration. In conditions of heavy fluid loading, which typically occurs in underwater applications, the energy imparted to the structural motions can be large, and the subsequent scattering of ‘surface waves’ at mechanical discontinuities is frequently an important secondary source of sound. In this paper general formulae are developed for the structural and acoustic edge-noise when the control surface is modelled by a semi-infinite, thin elastic plate which can support bending waves. Numerical results are given for steel plates in air and in water. In the latter case it is shown that, when the frequency is smaller than the coincidence frequency the bending wave power exceeds the total sound power generated at the edge by 20–40 dB, independently of the mean flow velocity, so that sound generated by secondary scattering may then be the dominant source of acoustic radiation.

Device for generating pseudo sound for electric vehicle

Abstract: PURPOSE:To provide a pseudo sound generating device for an electric vehicle, whereby the pseudo sound implying starting sound, running sound and accelerating/decelerating sound while running which are suitable for the electric vehicle is generated and also pseudo sound quantity is adjusted in accordance with peripheral noise. CONSTITUTION:A pseudo sound selecting means 3 selects the sound of a pseudo sound source means 4 which generates a pseudo sound signal corresponding to the vehicle operation state of starting, running and accelerating/decelerating while running based on sensor information from a starting sensor 2A, a rotation number sensor 2B (or a speed sensor 2C) and an accelerator opening degree sensor 2D, a sound quantity changing-over means 5 for adjusting a pseudo sound signal level is controlled and pseudo sound is generated from speakers 7 and 9 with amplifiers 6 and 8. A noise detecting means 10 for detecting peripheral noise is provided so as to control a sound quantity change-over means 5 in accordance with the noise level.

Active sound control systems and sound reproduction systems

Abstract: With reference to FIG. 1, an active sound control system comprises a loudspeaker LS having an input qs and operable to generate sound waves for interference with unwanted sound so as to produce a region close to the user of the system in which the perceived sound is substantially reduced. A monitoring microphone ro is positioned closer to the loudspeaker LS than to the region of sound reduction. Loudspeaker control means for controlling the input qs to the loudspeaker LS operate to energise the loudspeaker such that the sound waves emitted by the loudspeaker substantially cancel the unwanted sound waves in said region. The loudspeaker control means includes a signal processing means (FIG. 3) arranged to simulate a microphone output that would be obtained if that microphone, instead of being positioned closer to the loudspeaker LS than the user, were to be positioned in a notional position ra relatively close to the user. The resulting simulated or virtual microphone output is then used to control the signal fed to the loudspeaker input qs.

Computation of the acoustic radiation from bounded homogeneous flows

Abstract: A numerical study of the problem of sound radiation from isotropic turbulence is carried out. The hybrid DNS approach which combines direct numerical simulation (DNS) of turbulence with an acoustic analogy for the far-field sound is used as the computational tool. The feasibility of the hybrid DNS approach for the computation of the instantaneous acoustic pressure is demonstrated. Preliminary results indicate that the sound is predominantly associated with the energy-containing scales of motion. Furthermore, it appears that the acoustic output of isotropic turbulence is less than that of subsonic jets.

Antificial running sound generating device for electric vehicle

Abstract: PURPOSE:To provide an artificial running sound generating device for electric automobile to make the outside persons perceive the approaching of a vehicle, as well to give a reference to a driver when he drives the vehicle, and to generate an artificial sound that gives no unpleasant feeling to the occupants in the vehicle. CONSTITUTION:An artificial sound signal having a frequency corresponding to the motor rotation frequency detected by a motor rotation frequency sensor 12, and an amplitude corresponding to the accelerator opening detected by an accelerator opening sensor 24; and an artificial sound signal having a frequency corresponding to the car speed detected by a car speed sensor 14, and an amplitude corresponding to the accelerator opening; are produced by a computer 16, and they are output from a speaker 20 through an amplifier 18. And it is selected whether the artificial sound is made in the artificial sound depending on the motor rotation frequency, or that depending on the car speed, by a switch provided in the computer 16. In this case, the above selection is not made, but an artificial sound including the frequency depending on the motor rotation frequency, and the frequency depending on the car speed may be output.

Method and device in acoustic flow measurement for ensuring the operability of said measurement

Abstract: Method and device for acoustic flow measurement for measurement of the flow velocity (v) of gases and/or of quantities derived from same. A long-wave sound is transmitted into the measurement pipe (10) and, by means of two sound detectors (14a, 14b) placed at a certain distance (L) from one another in connection with the measurement pipe (10), the sound signals that propagate in the gas flow downstream and/or upstream are detected, the flow velocity (v) of the gas that flows in the measurement pipe (10) being determined by means of correlation of said sound signals. A sound speed co(T) in a medium at rest, which sound speed has been standardized or will be standardized for a certain temperature, is stored in the memory (20M), and the flow velocity (v) and the other quantities that may be derived from same, if any, are computed, at least in situations of disturbance, by means of the detected downstream speed vd or of the detected upstream speed vu and by means of said sound speed at rest co(T) stored in the memory (20M).

A comparison of error sensor strategies for the active control of duct noise

Abstract: A theoretical comparison of a number of error sensor strategies is undertaken for active control of periodic noise in a hard‐walled rectangular duct. Error sensor strategies investigated include the minimization of pressure at a point, the total real acoustic power output, and an estimate of the acoustic potential energy. A new error sensor strategy is also proposed and investigated. The strategy is based upon minimization of the power flow determined by a modal decomposition of the duct sound field. The error sensor strategies are analyzed for both plane‐wave and multimode sound fields, and for a range of duct termination conditions. The criterion used to assess the error sensor strategies is the minimization of the sound field downstream of the control sources.

Green's solution of the acoustic wave equation for a circular expansion chamber with arbitrary locations of inlet, outlet port, and termination impedance

Abstract: The acoustic characteristics of a circular expansion chamber whose inlet and outlet are situated on arbitrary locations of the chamber, i.e., the side wall or the face of the chamber, are analyzed based on the Green’s function of a chamber with homogeneous boundary conditions. The Green’s function is found by considering the boundary condition of the walls as rigid except at the location of the source, which is assumed to be a uniform volumetric acoustic source. The complete solution that determines the sound pressure distribution, intensity, and sound power pattern inside of the chamber are found. The solutions are compared with those based on the modal expansion techniques for the aforementioned cases. To verify the solutions, experiments were also performed, which determines the transmission loss of the expansion chamber. Side‐inlet/side‐outlet, face‐inlet/side‐outlet chambers were tested. A two‐microphone method was used to accurately determine the transmission losses of the chambers. The Green’s solu...

Method and apparatus of determining the sound transfer characteristic of an active noise control system

Abstract: A method and apparatus of determining the transfer characteristic in an active-noise-control system, which involves generating white noise at an end of a one-dimensional sound field that is defined by a linear ventilating system in which sound travels essentially parallel to the extended direction of the system; equalizing the transfer characteristic of the one-dimensional sound field and generating cancelling sound, according to an inverse of the transfer characteristic, to cancel the white noise and prevent noise being output from the other end of the one-dimensional sound field; continuously preventing the noise output and measuring the characteristic data of the one-dimensional sound field at, at least, one measuring point in the one-dimensional sound field; and calculating the transfer function of the one-dimensional sound field in the noise-output-prevented state, according to the characteristic data of the sound field.

Silencer arrangement for combustion engines

Abstract: A silencer arrangement for a combustion engine (1) whose exhaust gases are discharged via an exhaust pipe (3) comprises a microphone (9), a tachometer (11) for the engine speed, a control unit (13) and a loudspeaker enclosure (19) The loudspeaker enclosure accommodates two loudspeakers (15, 17) secured to a partition (21) The partition divides the volume of the loudspeaker enclosure into two subvolumes (23, 25) The subvolumes communicate with one another via a tube (27) in order to reduce the electric power required to obtain the desired acoustic power of the sound emitted by the loudspeaker enclosure One of the subvolumes (25) is acoustically coupled to a tube (33) One end (35) of the tube is situated near the end (7) of the exhaust pipe (3) The sound issuing from the loudspeaker enclosure via the tube interferes with the exhaust-gas sound A Helmholtz resonator (41) is acoustically coupled to the tube (33) in order to suppress undesired resonances in the tube (33) The Helmholtz resonator contains such an amount of an acoustic damping material (43) in the form of glass wool or rock wool that the quality factor QHelmh of the Helmholtz resonator lies between the values 1 and 3

Sound environment simulator and a method of analyzing a sound space

Abstract: The present invention discloses a sound environment simulator including a sound field analyzing unit, a sound field reproducing unit, and an output unit. The sound environment analyzing unit divides the solid surfaces of a space to be analyzed into a set of sections to compute the volume of reflected sounds with a sound absorption coefficient of walls and form factors. It further computes time series data related to the arrival volume of sounds emanated from a certain sound source to the sound receiving point. An impulse response computing unit in the sound field reproducing unit transduces the time series data into an impulse response. Accordingly, the sound field reproducing unit convolutes the impulse response on a dry source in accordance with data related to a listener's position inputted from an associated virtual reality equipment to generate a reproduced sound over a headphone.

Method for determining the propagation time (delay time) of sound signals, and a sound-wave propagation-time determining device

Abstract: A method for determining the propagation time of sound signals over a measurement path between at least one sound transmitter and at least one sound receiver comprises a reference transmission signal being formed which is equivalent to the measurement sound signal emitted into the measurement path and said signal being applied to the sound receiver after passing through the reference path, such that the effect corresponds to the reception of the measurement sound signal which is passed over the measurement path.

To absorb or not to absorb: Control source power output in active noise control systems

Abstract: This paper addresses the problem of finding a common link between actively attenuating noise in a variety of acoustic environments, such as in free space or in ducts, using vibration or acoustic control sources. It is shown that if acoustic reciprocity holds between each point on the primary source and each point on the control source, then the acoustic power output of the control source under optimal conditions will always be zero, with the converse also true. This concept is demonstrated for systems operating in free space, using both acoustic and vibration control sources, and for systems operating in a semi‐infinite duct with a nonrigid termination. The physical meaning of this concept for the employment of vibration control sources, applied directly to a vibrating structure in an effort to attenuate the radiated sound field, is shown.

A numerical method for noise optimization of engine structures

Abstract: A numerical procedure is described for optimizing finite element models of engine structures for minimum noise radiation. A statistical technique is used to select sample points in a multi-dimensional design variable space from which an approximating response surface is derived. Optimization of this analytic model is then carried out interactively with variable bounds and constraints as required to meet design objectives. The underlying noise analysis calculation uses a modal analysis algorithm to determine the surface vibration velocity and hence the radiated sound power. It incorporates a sophisticated procedure to determine the forces applied by the crank train to the cylinder block and head. Although computationally intensive, useful design studies are now practical using concept level finite element models.