Showing papers on "Sound intensity published in 1981"

Elements of acoustics

Abstract: CHAPTER TWO Basic Properties of Acoustic Waves 2.1 Ideal Fluids 2.2 Linearization 2.3 Uniform Fluids 2.4 One-Dimensional Plane Waves Speed of Sound in a Perfect Gas Speed of Sound in Other Fluids Relationships between Acoustic Quantities 2.5 Monochromatic Waves Plane, One-Dimensional Monochromatic Waves Plane, Monochromatic Waves in Three Dimensions Relation between Variables in a Monochromatic Wave Time Averages 2.6 Fourier Analysis Periodic Waveforms —Fourier Series Nonperiodic Functions—Fourier Transform 2.7 Acoustic Energy Energy Density Acoustic Intensity Reference Levels

Cross‐spectral method of measuring acoustic intensity by correcting phase and gain mismatch errors by microphone calibration

Abstract: The accuracy of measuring acoustic intensity using two closely spaced microphones is examined. The phase and gain mismatch errors are corrected by measuring the transfer function between the two microphone systems exposing them to the same sound (phase and pressure levels) over a wide range of frequencies. The accuracy of the measurement method was verified by creating a sound field in an anechoic room and by generating plane‐wave propagation inside a long length of pipe with an anechoic termination. The measurement accuracies were very satisfactory. This method has the advantage of eliminating the recording and processing of two sets of data required in the circuit switching technique.

The eod sound response in weakly electric fish

Abstract: 1. A spontaneous EOD response to sound is described in two gymnotoids of the pulseElectricOrganDischarge (EOD) type,Hypopomus andGymnotus, and in one mormyrid,Brienomyrus (Figs. 2–4). 2. In all three species, the EOD response to the sound onset was a transient EOD rate increase. In the low EOD rateHypopomus (3–6 EODs/s at rest) the first, second, or third EOD interval following sound onset was significantly shorter than the average EOD interval before stimulation. The shortest latency found was 100 ms, the longest ca. 1.2 s.Gymnotus (around 50 EODs/s at rest) responded similarly, but the third interval after sound onset was the first to be affected even at highest intensities (shortest latencies approx. 60 ms; latencies > 0.5 s at low sound intensities). InBrienomyrus (4–8 EODs/s at rest) the response occurred already at the first EOD interval after sound onset. 3. An EOD sound response was recorded inHypopomus and inGymnotus up to 5,000 Hz sound frequency (in oneGymnotus individual: up to 7,000 Hz). Due to technical limitations the low frequency limit of the response could not be exactly determined: the fishes responded well even below 100 Hz.Hypopomus had its maximum sensitivity around 500 Hz (Fig. 5),Gymnotus around 1,000 Hz (Fig. 6). 4. In all three species the EOD sound response was graded with sound intensity (Hypopomus: Fig. 7). 5. No EOD response to sound was found in two gymnotoids of the wave type,Eigenmannia andApteronotus, and in the gymnotoid pulse fishRhamphichthys. A criterion is proposed by which it should be possible to predict whether or not a weakly electric fish species will show the EOD sound response. 6. It is concluded that the EOD response to sound is similar to EOD responses to other kinds of stimulation (light, touch, vibration, food, and even electrical). The possible biological function is discussed.

Underwater Hearing in the Frog, Rana Catesbeiana

Abstract: Comparable auditory sound pressure level (SPL) and sound intensity level(SIL) threshold curves were determined in air and under water in Ranacatesbeiana . Threshold curves were determined using chronic metal electrodeimplants which detected multi-unit responses of the torus semicircularis toincident sound. In terms of SPL, hearing thresholds in water and air aresimilar below 0.2 kHz. Above 0.2 kHz, the sensitivity under water falls of fat about 16 dB/octave to reach an average loss of about 30 dB above 0.4 kHz. In terms of SIL, the organism is about 30 dB more sensitive under water than in air below 0.2 kHz and equally sensitive in air and water above 0.4 kHz.The relative merits of the two measures are discussed and an attempt is made to relate the results to morphology of the middle and inner ears. This report is the first to compare aerial and underwater hearing abilities in any organism using electrode implants.

Damped acoustic transducers with piezoelectric drivers

Abstract: A tuned acoustic directional transducer for transmitting and receiving airborne sound, which provides enhanced efficiency and reduced cost without undue narrowing of bandwidth, makes use of an acoustic transducer element (2) coupled to a plate (10) having a higher order flexural mode resonance at approximately the desired frequency of operation, the plate being coupled to the air through low-hysteresis acoustic propagation material having an acoustic impedance much less than that of the plate and much greater than that of the air. The material is disposed so that in the desired direction of propagation there is no substantial reduction of sound intensity in the far field resulting from cancellation occasioned by interaction of sound radiated from adjacent antinodal zones. Preferably the thickness of the material is such that it acts as an efficient acoustic impedance matching transformer. Preferably, the transducer element is piezoelectric and coupled to the center of a circular plate to which the coupling material is applied in rings (16, 18, 20).

Arrangement for damping and absorption of sound in rooms

Abstract: An acoustical system for damping and absorption of sound in rooms to provide a sound damping even at very low frequencies, e.g. 50 Hz, and simultaneously improve speech comprehension in the entire room by reduction of the resonance time. The acoustic absorption can be varied to vary the resonance time over the entire part of the frequency area. The sound absorbents 14 in the form of plates, mats or similar constructions, are arranged at an angle in at least one corner area 11 formed by the walls 12 and ceiling 13 of the room. In the corner area 11 behind the absorbent 14, an air volume is trapped so that the absorbent due to the sound influence has a membrane effect. The inclination and position of each absorbent 14 can be varied individually or in groups.

Method and device for the localization and analysis of sound emissions

Abstract: A method for localizing and analyzing sound emissions, wherein the position of the sound emission source is determined by incoming sound pulses at various measuring locations. The arrival time of a pulse or of a pulse characteristic is measured in three or more adjacent portions of each measuring location whose width is smaller than the expected sound field diameter. From this, the propagation time difference for the portion of each measuring location is determined and the sound arrival direction is determined from these propagation time difference values for each measuring location. Subsequently, the position of the sound emission source is determined from these direction values and the position coordinates of the measuring locations. The device for carrying out this method has three or more separate converter elements (1) for each receiver measurement head (E) whose total width is smaller than the expected sound field diameter.

System for maintaining high resonance during sonic agglomeration

Abstract: A sonic agglomeration system wherein high sound intensity and resonance are maintained with a low power input. These functions are attained through the use of a chamber feed-horn design that promotes resonance and maximized the efficiency of sound transfer between a sound producing compression driver and a resonant chamber. A digital controller maintains efficient resonance in the chamber and an efficient agglomeration rate constant by making adjustments in the frequency, sound amplitude and nuclei injection rate of the system.

Oceanographic measurement system

Abstract: An acoustic ocean measuring system is disclosed which uses measurements of sound intensity to locate and measure ocean anomalies. Several free-floating sound pulse emitting floats are placed in the ocean area to be measured; the position of the floats can be determined by well-known ranging techniques. Several hydrophones are positioned either in the immediate area or at distant locations to receive the sound pulses. A fixed number of received sound signals are electronically processed to obtain peak intensity signals. A fixed set of peak signals received from the floats over a fixed period of time are used to generate a trend line which can be used to predict the peak intensity received from the position data. The actual received intensity measurements are compared to the predicted measurements; substantial deviations from the predicted values are used to locate and measure parameters of ocean anomalies.

Aerosol agglomeration in high-intensity acoustic fields

Abstract: The acoustic agglomeration kernels in various regimes have been evaluated for various parameters, namely, aerosol concentration, median diameter, standard deviation, acoustic intensity, acoustic frequency, ambient temperature, and pressure. It is found that with the existence of the acoustically induced turbulence, turbulent inertial interaction is the dominant process for agglomeration of aerosol. A computer code has been developed to furnish a comparison of relative importance of the principal agglomeration mechanisms at different acoustic intensities and particulate emission mass loadings. Finally, an experimental investigation has been performed to verify the theory of aerosol deposition and agglomeration in high-intensity acoustic fields. Using a laboratory-scale transmissometer for the continuous light-opacity measurements, separate experimental runs have been directed to investigate the effects of acoustic intensity I , frequency f , and massloading M . In the operating range of I = 160–164 db, f = 500–2200 Hz, and M = 10–30 g/m 3 , the experimental data show a fairly good agreement with the theoretical results. It is also revealed that, under the same operating conditions, the standing-wave operation is more effective than the traveling-wave operation.

Acoustic intensity measurement apparatus and method including probe having ambient noise shield

Abstract: Acoustic intensity measuring apparatus for determining sound energy intensity utilizing a probe having a pair of microphones and an associated ambient noise shield.

Emergency sound detector device

Abstract: A low-pass filter passes a spectrum of electrical signals which are utilized to establish a threshold level with which electrical signals having frequencies in a relatively higher range are compared to determine if a warning sound is present in the sounds in the vicinity of a receiver unit for receiving the ambient sound. If the rectified magnitude of the signals having the higher frequencies exceeds the rectified and variably adjusted magnitudes of the signals having lower frequencies, a visual indication is given to communicate the existence of a warning sound in the ambient sounds.

Neurophysiological Mechanisms of Intensity Discrimination in the Goldfish

Abstract: The detection of changes in sound intensity (ΔI) is one of the fundamental auditory capacities for which auditory systems have presumably been “designed” throughout evolution Questions of the neural representations of sound intensity, and the ways these are processed by the brain are basic to an analysis of sensory coding The psychophysical literature contains two major observations: (1) The ratio ΔI/I is approximately constant for noise signals within a wide range of I values (ie, Weber’s law holds) (Miller 1947, Rodenburg 1972) (2) For tone signals, ΔI/I declines somewhat at larger I values (ie, there is a “near miss” to Weber’s law) (Reisz 1928, McGill and Goldberg 1968, Jesteadt, Wier, and Green 1977, Steigel 1977)

The Use of Acoustic-Intensity Scans for Sound Power Measurement and for Noise Source Identification in Surface Transportation Vehicles

Abstract: The results are reported of near-field, acoustic-intensity scans of a diesel-engine truck, chassis-mounted passenger-car engines, and a railroad locomotive. The measurements were made using the two-microphone, cross-spectral method of measuring acoustic intensity. The results demonstrate the value of the method for measuring the overall sound power of a vehicle as well as for identifying its component noise sources. A review of theory and methodology is provided.

The role of acoustic tube resonances in the radiation of sound from circumferentially ribbed truck tires

Abstract: While in contact with the pavement surface, the grooves of circumferentially ribbed tires form tubes open at both the leading and trailing edges of the tire contact patch These tubes efficiently radiale sound at the fundamental resonant frequency, corresponding to an acoustic wavelength equal to one half of the tube length, and at the higher harmonic frequencies This behavior was studied with acoustic intensity measurements made alongside a moving straight rib (HCR) truck tire using the technique described in a previous presentation [L J Oswald and P R Donavan, J Acoust Soc Am Suppl 1, 67, S71 (1980)] These data show a 3 to 7 dB reduction from 500 to 2500 Hz in the narrow‐band acoustic intensity spectrum when the resonant‐tube radiation is eliminated with open cell foam placed in the grooves Further, consistent with the dipolelike radiation from the tube ends occurring at the odd‐numbered tube harmonics, distinct nulls in the acoustic intensity were measured alongside the center of the contact patch at these frequencies The influence of resonant tube radiation is also discussed for commercial wavy rib truck and passenger car tires

The Use of Existing and Advanced Intensity Techniques to Identify Noise Sources on a Diesel Engine

Abstract: Existing techniques for identifying noise sources are reviewed. One such technique (the lead-wrapping approach) was used to source-identify a diesel engine and measure the sound power radiated from the major surfaces. Two new advanced techniques (surface intensity and acoustic intensity) were used to measure the sound power radiated from the same major surfaces. The conventional lead-wrapping and new intensity results were compared. The advantages of the new intensity techniques are described and suggestions made for reducing the noise of this and other similar diesel engines.

Sound wave propagation time measuring system - uses phase-shift of wave train at centre of successive bursts

Abstract: The system uses sound bursts with the delay determined from the phase shift of the wave train at the centre of each burst, between the two end sections exhibiting attenuation due to the electromagnetic transducer. The wavelength of the sound waves is greater than the phase-shift corresponding to the max. permissible delay and the sound bursts are pref. modulated by continuous base frequency. The system is used to measure distances or the characteristics of the medium through which the sound waves are propagated. It can also be used to measure the flow rate of the propagation medium.

Acoustic Intensity Measurements of Transient Noise Sources

Abstract: The theoretical background to the measurement of sound energy flow generated by transient sources, such as impact machines, will be presented. Various means of implementing the estimation process will be discussed and reference will be made to the problems of field measurement. Results of measurements made on a drop forge and other impulsive sources will be presented. It will be shown that directly radiated and reverberant sound can be satisfactorily separated.

An acoustic transducer system

Abstract: A broadly tuned directional acoustic transducer system for transmitting and receiving airborne sound, which provides enhanced efficiency and reduced cost without undue narrowing of bandwidth, makes use of an acoustic transducer element (2) coupled to a vibratable member (10), e.g. a plate, having a higher order flexural mode resonance at approximately the desired frequency of operation, the vibratable member being coupled to the air through low-hysteresis acoustic propagation material having an acoustic impedance much less than that of the vibratable member and much greater than that of the air. The material is disposed so that in the desired direction of propagation there is no substantial reduction of sound intensity in the far field resulting from cancellation occasioned by interaction of sound radiated from I adjacent antinodal zones. Preferably the thickness of the material is such that it acts as an efficient acoustic impedance matching transformer. Preferably, the transducer element is piezoelectric and coupled to the centre of a disc-shaped vibratable member (10) to which the coupling material is applied in rings (16, 18, 20).

A new method of measuring normal incident sound absorption characteristics of materials using acoustic tube

Abstract: A new method is presented for the measurement of normal incident sound absorption characteristics of materials using an acoustic tube. As the measuring principle, by measuring the signals of sound pressure at two points in the acoustic tube using two microphones, and by processing these signals either in time domain or in frequency domain, the incident wave and the reflected wave are equivalently separated. For the sound source, any of pure tone, random noise or impulse can be used in this measuring method. As a result of the experimental study by making measurements on two types of sound absorbing materials, it is ascertained that almost the same results can be obtained by this method as those measured by the ordinary standing wave method.

Noise Characteristics of Coannular Flows with Conventional and Inverted Velocity Profiles

Abstract: The results of the investigation of the noise characteristics of the exhaust jets from coannular nozzles with conventional and inverted velocity profiles are presented. Experiments were carried out on a series of coannular nozzles of equal primary and secondary area. The results of this study show that at high thrust level the coannular flows with inverted velocity profiles are quieter than those with standard velocity profiles at the same thrust and the same mass flow. The acoustic differences are much greater when the velocity ratio is produced by differences in the stagnation temperature rather than by differences in the stagnation pressure. Nomenclature A = area a0 = ambient speed of sound D = diameter / = sound intensity IL = intensity level m = mass flow rate P = pressure R = radial distance Th = total thrust U — local mean velocity u' — turbulence velocity V — jet-exit velocity B = polar angle measured from flow axis II = pressure ratio, P0/Pa p = density Subscripts a = atmospheric c = convection e = exit 0 = stagnation or ambient p = primary 5- = secondary

Interaction of sound with noise in water II

Abstract: The prediction of the scattered intensity due to the nonlinear interaction between underwater sound and noise requires measurement of the complex intensity of the noise field. Such an experiment is made possible by use of the complex wattmeter. This paper describes an experiment in which the device is used to select the 2.8‐kHz component from a stable noise field and process the signal to produce a value for the component’s complex intensity. The resultant value is inserted into Westervelt’s interaction equation to yield a value for the scattered intensity due to the interaction between the noise and a 2.7‐MHz plane wave. The predicted intensity is within 1 dB of the measured figure.

Measurement of acoustic intensity in the presence of one‐dimensional fluid flow

Abstract: This paper presents the results of an analytical and experimental investigation of the measurement of acoustic intensity in the presence of mean fluid flow. The investigation was necessitated by the fact that an acoustic intensity measurement technique with mean fluid flow is not available. Munro and Ingard [J. Acoust. Soc. Am. 65, 1402–1406 (1979)] have developed a formulation for this problem; but no experimental data or verification is given. In this paper, two independent formulations for acoustic intensity in a duct with mean fluid flow using the two‐microphone cross‐spectral density method are developed. In order to evaluate and compare our formulations with the Munro and Ingard expression, we have conducted an experiment for the case of one‐dimensional, irrotational, isentropic mean flow in a duct over 0–0.15 Mach range and for frequencies from 300 to 800 Hz. All these formulations yield similar values for acoustic intensity, within experimental errors. Although it is still premature to draw definite conclusions regarding the significance of additive terms to the nonflow acoustic intensity, some insight based on our preliminary experimental results has been gained.

Separated flow noise of a flat plate at large attack angles

Abstract: Flow noise associated with separated flow of a flat plate with large attack angles was studied experimentally to obtain its acoustic characteristics and to understand its generation mechanism. The acoustic features show that the separated flow noise could be attributed to acoustic dipole sources associated with the wall-pressure fluctuations on the plate surface. The time derivative of the fluctuating wall-surface pressure is highly correlated with the associated acoustic pressure. The noise intensity source strength is proportional to the mean-square time derivative of the fluctuating surface pressure and its correlation area, being proportional to the sixth power of the oncoming flow velocity and distributed uniformly over the plate surfaces. The associated acoustic intensity is well predicted by these noise source strength distributions.