The effects of sound level and vibration magnitude on the relative discomfort of noise and vibration

The relative discomfort caused by noise and vibration, how this depends on the level of noise and the magnitude of vibration, and whether the noise and vibration are presented simultaneously or sequentially has been investigated in a laboratory study with 20 subjects. Noise and vertical vibration were reproduced with all 49 combinations of 7 levels of noise and 7 magnitudes of vibration to allow the discomfort caused by one of the stimuli to be judged relative to the other stimulus using magnitude estimation. In four sessions, subjects judged noise relative to vibration and vibration relative to noise, with both simultaneous and sequential presentations of the stimuli. The equivalence of noise and vibration was not greatly dependent on whether the stimuli were simultaneous or sequential, but highly dependent on whether noise was judged relative to vibration or vibration was judged relative to noise. When judging noise, higher magnitude vibrations appeared to mask the discomfort caused by low levels of noise. When judging vibration, higher level noises appeared to mask the discomfort caused by low magnitudes of vibration. The judgment of vibration discomfort was more influenced by noise than the judgment of noise discomfort was influenced by vibration.     

Development of vibration signature analysis using multiwavelet systems

In this paper the vibration analysis for local faults and transient phenomena detection, using multiwavelet systems, is developed. Unlike the scalar wavelet systems, in which their coefficients are scalar parameters, the transformation coefficients of multiwavelet systems are vector valued, and their calculation requires specialized techniques. In this investigation, having considered the technique used to obtain the scalar wavelet system coefficients, the transformation coefficients of the multiwavelet system are calculated, and by applying the method to artificial vibration signals, decomposition of the signal into different multiscale and multiwavelet functions (as introduced by Donovan, Geronimo, Hardin and Massopust) is examined, as well as the capability of this multiwavelet system for transient phenomena detection. By analyzing the vibration signal of a faulty gearing system the applicability of Donovan, Geronimo, Hardin and Massopust multiwavelet system for local fault detection of the mechanical systems is shown. The results confirm that using the multiwavelet system, not only can the fault in the gearing system be diagnosed, but also its location can be determined precisely.     

Multi-purpose explosion chamber with sound muffling and vibration cutting means

Abstract

An explosion chamber is operating for more than 13 years successfully. The chamber is used for procucing wBN powder and various dynamic high pressure experiments. The capacity of the chamber is 200 cubic meter by volume and 10 kg by the quantity of the explosives to be exploded. Safety means are equipped sequentially, transmitted sound level is less than 65 db at 60 m point from the chamber and earth vibrations cannot be detected at its periphery. The strength of the chamber was designed by simple static gas pressure model.     

Active control of sound radiated by a submarine in bending vibration

This paper theoretically investigates the use of inertial actuators to reduce the sound radiated by a submarine hull in bending vibration under harmonic excitation from the propeller. The radial forces from the propeller are tonal at the blade passing frequency and are transmitted to the hull through the stern end cone. The hull is modelled as a fluid loaded cylindrical shell with ring stiffeners and two equally spaced bulkheads. The cylinder is closed by end-plates and conical end caps. The actuators are arranged in circumferential arrays and attached to the prow end cone. Both Active Vibration Control and Active Structural Acoustic Control are analysed. The inertial actuators can provide control forces with a magnitude large enough to reduce the sound radiated by the vibrations of the hull in some frequency ranges.     

Experimental studies on sound and vibration of a two-tone Chinese Peace Bell

In order to examine whether the characteristics of the bell are coincident with the design and make some constructive suggestions for the tuning of bell, the frequency characteristics of sound and the vibrational modes of a two-tone Chinese Peace Bell have been studied. With Welch's spectral estimate, the main partials of radiated sound of the bell have been found out. With time-frequency analysis, the changes of the spectrum with time have been shown. By conditional mean frequency (CMF) of the spectrogram of the sound, the change in the pitch of the bell has been discussed. With an accelerator, the vibration distributions on the different points of the bell have been measured. With short time spectrum analysis, the vibrational modes at different frequencies have been reconstructed.     

Responses of pigeon vestibular nerve fibers to sound and vibration with audiofrequencies

Single unit recordings were made from the nerve branch innervating the crista in the horizontal semicircular canal of a pigeon. The vestibular organ was either stimulated with sound through the ear canal or with a vibrator in contact with the membraneous ampulla roof. Units responding to sound or vibration showed tuning with a best frequency of approximately 0.7 kHz. The average low-frequency slope of the tuning curves is--16 dB/oct; the average high-frequency slope 20 dB/oct. The threshold amplitude for vibrator stimulation is 30 nm. This value comes close to the calculated threshold value for cupula deflection in the human semicircular canal.     

Two-dimensional model of vocal fold vibration for sound synthesis of voice and soprano singing

Voiced sounds were simulated with a computer model of the vocal fold composed of a single mass vibrating both parallel and perpendicular to the airflow. Similarities with the two-mass model are found in the amplitudes of the glottal area and the glottal volume flow velocity, the variation in the volume flow waveform with the vocal tract shape, and the dependence of the oscillation amplitude upon the average opening area of the glottis, among other similar features. A few dissimilarities are also found in the more symmetric glottal and volume flow waveforms in the rising and falling phases. The major improvement of the present model over the two-mass model is that it yields a smooth transition between oscillations with an inductive load and a capacitive load of the vocal tract with no sudden jumps in the vibration frequency. Self-excitation is possible both below and above the first formant frequency of the vocal tract. By taking advantage of the wider continuous frequency range, the two-dimensional model can successfully be applied to the sound synthesis of a high-pitched soprano singing, where the fundamental frequency sometimes exceeds the first formant frequency.     

Infrasonic sound pressure in dwellings at the Helmholtz resonance actuated by environmental noise and vibration

The Helmholtz resonator effect of a room with an open window or ventilation duct has been studied theoretically and experimentally. The effect results in a sound pressure buildup at infrasonic frequencies. For comparison, the frequencies of the standing-wave room resonances are above the infrasonic range for residential dwellings. The relations between the sound pressure inside a room and outside (environmental) sound pressure or vibration acceleration have been calculated for the third-octave frequency band incorporating the Helmholtz resonance frequency. The experiment on a small-scale model illustrated the Helmholtz resonator effect caused by environmental vibration.     

Acoustically induced vibration of,and sound radiation from,beams inside an enclosure

The velocity response of a single cylindrical beam to pure tone sound in a rectangular reverberation chamber is analysed. The variation of the response with position within the chamber and the effect of proximity of other similar, parallel beams is considered. A reciprocity relation is established between the response of a beam to sound in the chamber and the sound radiation by such motion when otherwise generated; this relation is found to be valid even for non-diffuse fields, below the Schroeder “large room” frequency (i.e., above this frequency, the average frequency spacing between modes is less than one-third of the bandwidth of a typical mode [1]). The mean square velocity response, averaged over all possible beam positions within the chamber, is found to be directly proportional to the radiation loss factor of that vibrational mode, and inversely proportional to (frequency)³. The maximum normalized response occurs when the beam is excited in its fundamental vibrational mode. One application is to the estimation of fatigue life of heat exchanger tubes in gas-cooled nuclear reactors; the large number of tubes necessitates an estimate of the variation of the tube response with position within the exchanger casing. Another important application is in a reverberation chamber; in many cases a suitable direct excitation experiment is very difficult, or even impossible to perform, while the corresponding reciprocal experiment is relatively easy.     

The diffuse sound field in energetic analysis

Measuring the degree of diffuseness of a sound field is crucial in many modern parametric spatial audio techniques. In these applications, intensity-based diffuseness estimators are particularly convenient, as the sound intensity can also be used to obtain, e.g., the direction of arrival of the sound. This contribution reviews different diffuseness estimators comparing them under the conditions found in practice, i.e., with arrays of noisy microphones and with the expectation operators substituted by finite temporal averages. The estimators show a similar performance, however, each with specific advantages and disadvantages depending on the scenario. Furthermore, the paper derives an estimator and highlights the possibility of using spatial averaging to improve the temporal resolution of the estimates.     

Reception plate method for characterisation of structure-borne sound sources in buildings: Installed power and sound pressure from laboratory data

In a companion paper, a laboratory method is described to obtain the structure-borne sound power of machines before they are installed in heavy-weight buildings. The laboratory method is based on the concept of the reception plate. In this paper, the method is shown to provide appropriate input data for the prediction of the installed structure-borne power, and thence the resultant sound pressure level in rooms removed from the room containing the machine. Case studies of two common sources are described: a whirlpool bath and a water cistern. It is shown that the method can be incorporated into recently proposed standard prediction models and that sound pressure levels in buildings can be predicted.     

Optical microdisplacement measurement and vibration analysis

An optical apparatus for microdisplacement measurements has been developed. It is characterized by a very small observation area of several square micrometres. It offers 1000 measurement points and its resolution, depending on the power of the frontal objective, ranges from 2 nm to 100 nm. The same apparatus can be used for measurement of the amplitude and phase of the vibration of a mechanical part. The frequency domain extends from 20 to 100 000 Hz.The principle of measurement is as follows. A displacement of the surface examined entails a defocusing which is expressed by the modification of the light flow received by a differential photodiode. If the surface vibrates, the light flow is modulated and the vibration is translated by a modulation of the photoelectric currents.     

Application of the time dependent finite difference theory to the study of sound and vibration interactions in ducts

The time dependent finite difference theory is extended to the solution of the acoustic wave equation in rectangular ducts when acoustic/structural interactions are allowed at a duct wall. The treatment of the boundary condition which describes the coupling is examined, and the stability of the procedure is studied and found to depend on the nature of this coupling. The convergence of solutions is discussed as a function of the discretization of the solution domain, particularly at frequencies approaching resonance.     

Reduction of sound transmission into a circular cylindrical shell using distributed vibration absorbers and Helmholtz resonators

A modal expansion method is used to model a cylindrical enclosure excited by an external plane wave. A set of distributed vibration absorbers (DVAs) and Helmholtz resonators (HRs) are applied to the structure to control the interior acoustic levels. Using an impedance matching method, the structure, the acoustic cavity, and the noise reduction devices are fully coupled to yield an analytical formulation of the structural kinetic energy and acoustic potential energy of a treated cylindrical cavity. Lightweight DVAs and small HRs tuned to the natural frequencies of the targeted structural and acoustic modes, respectively, result in significant acoustic and structural attenuation when the devices are optimally damped. Simulations show that significant interior noise reduction can only be achieved by adding damping to both structural and acoustic modes, which are resonant in the frequency bandwidth of interest. In order to be independent of the azimuth angle of the excitation and to avoid unwanted modal interactions, the devices are distributed evenly around the cylinder in rings. This treatment can only achieve good performance if the structure and the acoustic cavity are lightly damped.     

Acoustical analysis and model-based sound synthesis of the kantele

The five-string Finnish kantele is a traditional folk music instrument that has unique structural features, resulting in a sound of bright and reverberant timbre. This article presents an analysis of the sound generation principles in the kantele, based on measurements and analytical formulation. The most characteristic features of the unique timbre are caused by the bridgeless string termination around a tuning pin at one end and the knotted termination around a supporting bar at the other end. These result in prominent second-order nonlinearity and strong beating of harmonics, respectively. A computational model of the instrument is also formulated and the algorithm is made efficient for real-time synthesis to simulate these features of the instrument timbre.     

Auditory profile analysis of irregular sound spectra

The discrimination of changes in the shapes of sound spectra is reported. The change was always an intensity increment to the 948-Hz component of a multitone complex. First, the ability of naive listeners to learn to discriminate a change in a "regular" background or reference spectrum (equal-level tones equally spaced in logarithmic frequency) was measured as a function of the number of trials. On the average, threshold improved about 10 dB over 3000 trials, with about 50% of the decrease in threshold occurring during the first 750 trials. In a subsequent series of experiments, the overall pattern of spectral shape of the background was varied randomly. Two kinds of perturbations in spectral shape were employed: Randomly choosing the frequencies of the reference spectra and randomly choosing the amplitudes of the components of the reference spectra. The experimental manipulations involved fixing the random spectra across a block of trials, varying the reference spectra from interval to interval of each trial, and providing extensive practice in discriminating specific randomly perturbed reference spectra. The results of the spectrum-learning and random perturbation experiments provide insight into the roles of critical band filtering, sensory variability, and short-term and long-term memory representations in auditory profile analysis. Further, the appropriateness of the generalization of a simple energy detection model is discussed.