Showing papers on "Sound transmission class published in 1995"

Active control of sound radiation using volume velocity cancellation

Abstract: The active control of sound transmission through a panel has been formulated using a near‐field approach. The effects of minimizing the sound power radiated by the panel and of canceling the net volume velocity of the panel are compared not only in terms of the reduction in sound radiation but also in terms of the change in the space average mean‐squared velocity of the panel and the space average mean‐squared pressure at its surface. Simulations of a thin panel excited by an incident acoustic plane wave and a piezoelectric control actuator show that volume velocity cancellation gives similar reductions in the transmitted sound power to the minimization of sound power radiation up to frequencies at which the size of the plate is about half an acoustic wavelength. The acoustic radiation is analyzed in terms of the radiation modes of the panel which are also used to explain spillover effects. Spillover, which leads to increases in the mean‐squared velocity of the panel and to increases in near‐field pressur...

Binaural synthesis, head-related transfer functions, and uses thereof

Abstract: The invention relates to improved methods and apparatus for stimulating the transmission of sound from sound sources to the ear canals of a listener, said sound sources being positioned arbitrarily in three dimensions in relation to the listener. In particular, the invention relates to new and improved methods for measurement of Head-related Transfer Functions, new and improved Head-related Transfer Functions, new and improved methods for processing Head-related Transfer Functions, and new methods of changing, or of maintaining, the directions of the sound sources as perceived by a listener. The measurement methods have been improved so that it is now possible to measure and/or construct Head-related Transfer Functions for which the time domain descriptions are surprisingly short and for which the differences from one individual to the other are surprisingly low. The new Head-related Transfer Functions can be exploited in any application concerning simulation of sound transmission, e.g. auralization of concert halls, measurement, simulation, or reproduction of sound, such as in binaural synthesis, e.g. for generation, by means of two sound sources, such as by headphones or by two loudspeakers, the perception of a listener that he is listening to sound generated by a multichannel sound system, such as a surround system, a quadraphonic system, a stereophonic system, etc, in the design of electronic filters used in, e.g. virtual reality systems, to simulate sound transmission from a virtual sound source to the ear canals of the listener, or, in the design of an artificial head that is designed so that its Head-related Transfer Functions approximate the Head-related Transfer Functions of the invention as closely as possible in order to make the best possible representation of humans by the artificial head, e.g. to make artificial head recordings of optimum quality.

Shallow-water sound transmission measurements on the New Jersey continental shelf

Abstract: Calibrated acoustic measurements were made under calm sea state conditions on the New Jersey shelf near the AM COR 6010 borehole, a surveyed area with known geophysical properties. The experiment was conducted in 73 m water with supporting measurements of salinity, temperature, and sound speed. Acoustic measurements were obtained with a vertical array of 24 hydrophones spaced equally at 2.5m intervals; one of which was near the bottom. A source towed at 1/2 the water depth transmitted one of two sets of four tones spaced between 50 and 600 Hz for each run to ranges of 4 and 26 km. The data were processed with both a Hankel transform and a high resolution Doppler technique to yield horizontal wave-number spectrum at several depths. Results were obtained along both constant and gradually varying depth profiles. Similar modal interference patterns were observed at the lower frequencies. The constant depth-profile radial results were compared to calculations performed with several shallow water acoustic models using geoacoustic profiles derived from geophysical parameters and shear wave inversion methods. Calculated and measured sound transmission results were found to agree.

Directional sound processing and interaural sound transmission in a small and a large grasshopper

Abstract: Physical mechanisms involved in directional hearing are investigated in two species of short-horned grasshoppers that differ in body length by a factor of 3s4. The directional cues (the effects of the direction of sound incidence on the amplitude and phase angle of the sounds at the ears) are more pronounced in the larger animal, but the scaling is not simple. At high frequencies (10s20 kHz), the sound pressures at the ears of the larger species (Schistocerca gregaria) differ sufficiently to provide a useful directionality. In contrast, at low frequencies (3s5 kHz), the ears must be acoustically coupled and work as pressure difference receivers. At 3s5 kHz, the interaural sound transmission is approximately 0.5 (that is, when a tympanum is driven by a sound pressure of unit amplitude at its outer surface, the tympanum of the opposite ear receives a sound pressure with an amplitude of 0.5 through the interaural pathway). The interaural transmission decreases with frequency, and above 10 kHz it is only 0.1s0.2. It still has a significant effect on the directionality, however, because the directional cues are large. In the smaller species (Chorthippus biguttulus), the interaural sound transmission is also around 0.5 at 5 kHz, but the directionality is poor. The reason for this is not the modest directional cues, but rather the fact that the transmitted sound is not sufficiently delayed for the ear to exploit the directional cues. Above 7 kHz, the transmission increases to approximately 0.8 and the transmission delay increases; this allows the ear to become more directional, despite the still modest directional cues.

Gas density does not affect pulmonary acoustic transmission in normal men.

Abstract: Fremitus, the transmission of sound and vibration from the mouth to the chest wall, has long been used clinically to examine the pulmonary system. Recently, modern technology has become available to measure the acoustic transfer function (TF) and transit times (TT) of the pulmonary system. Because sound speed is inversely proportional to the square root of gas density in free gas, but not in porous media, we measured the effect of air and Heliox (80% He-20% O2) breathing on pulmonary sound transmission in six healthy subjects to investigate the mechanism of sound transmission. Wide-band noise (75-2,000 Hz) was "injected" into the mouth and picked up over the trachea and chest wall. The averaged power spectra, TF, phase, and coherence were calculated using a fast Fourier transform-based algorithm. The phase data were used to calculate TT as a function of frequency. TF was found to consist of a low-pass filter property with essentially flat transmitted energy to 300 Hz and exponential decline to 600 Hz at the anterior right upper lobe (CR) and flat transmission to 100 Hz with exponential decline to 150 Hz at the right posterior base (BR). TF was not affected by breathing Heliox. The average TT values, calculated from the slopes of the averaged phase, were 1.5 +/- 0.5 ms for trachea to CR and 5.2 +/- 0.5 ms for trachea to BR transmission during air breathing. During Heliox breathing, the values of TT were 1.5 +/- 0.5 ms and 4.9 +/- 0.5 ms from the trachea to CR and from the trachea to BR locations, respectively. These results suggest that sound transmission in the respiratory system is dominated by wave propagation through the parenchymal porous structure.

Effects of panel boundedness on sound transmission problems

Abstract: A theory for sound transmission through a panel of finite width and infinite length mounted in a rigid baffle is formulated in order to discuss the effects of the panel boundedness on the sound transmission loss. The results calculated from a rigorous solution are presented as the frequency characteristics curves. However, it seems to be difficult to evaluate the sound insulation efficiency of the panel using the rigorous results, because of their violent peaks and dips owing to resonance. A method for averaging the response over any frequency band is discussed. The averaged response corresponds to the actual transmission measurement with a bandlimited excitation and allows one to evaluate the transmission characteristics from a viewpoint of practical noise control. The effects of the panel boundedness including a comparison with an infinite panel are also discussed by means of this method.

A generalized model for predicting the sound transmission properties of generally orthotropic plates with arbitrary boundary conditions

Abstract: Sound transmission is of significant concern in practical situations, such as building noise insulation or quietening of mechanical products. If the medium‐ and high‐frequency response are well mastered, it is not the case in the low‐frequency range where some discrepancies between experiments and theory remain sometimes unexplained. In view of these limitations, the scope of this work is to develop a generalized model which focuses on aspects particularly important in the low‐frequency range, namely (1) the finite size of the panel, (2) the orthotropy properties, and (3) the boundary conditions. A variational approach is adopted. The Hamilton functional is built starting with the general tensor relationships between stresses and strains for a generally orthotropic plate. The extremalization is performed using the Rayleigh–Ritz method in conjunction with a nonorthogonal polynomial basis in order to deal with general boundary conditions. The excitation is an acoustic plane wave of any incidence and the radiated field is calculated with an impedance matrix including the cross coupling terms. The different vibroacoustic indicators are the quadratic velocity of the plate, its radiation efficiency, and the transmission loss. The importance of including the intermodal interaction is clearly pointed out. It produces narrow peaks of transmission loss well above the classical mass law. The effect of the dimensions of the panels is shown rigorously and suggests that experimental results should be given in narrow‐band if one wants to get usable data. The model also allows, probably for the first time, the effect of the boundary conditions to be fully analyzed. Interestingly enough, the free‐free case gives a much bigger transmission loss in the low‐frequency range which gives an insight, when possible, for improving the transmission loss.

Active control of sound transmission through a plate using a piezoelectric actuator and sensor

Abstract: Active sound transmission control using a piezoelectric sensor and actuator on a thin plate is investigated experimentally. The plate made of aluminium covers the opening of an acoustic enclosure where a sound source is located. The exterior acoustic field is measured by a microphone array, which scans a hemispherical surface. The isolation performance of the passive plate is poor at its resonance frequencies. Sound transmission through the plate is actively controlled at the resonance frequencies. A one-sensor one-actuator control system minimizes the sensor output by applying a proper electric voltage to the actuator. Global sound reduction of 15-22 dB is achieved at the first three resonance frequencies by using the same sensor and actuator. Using a sensor at a different location, a reduction of 9 dB is obtained at a higher frequency. The relation between control performance and the coincidence of the responses of the transmitted sound and the sensor is briefly discussed based on the mode decomposition theory.

A time domain study of active control of sound transmission due to acoustic pulse excitation

Abstract: A time domain model for simulating the noise transmission through an elastic plate into a rigid cavity has been developed This model is used to study the noise attenuation capability of the filtered‐x least‐mean‐square (LMS) feedforward control algorithm for the case where the model is excited by an acoustic pulse Piezoelectric transducers (PZT’s) are considered to be bonded on the elastic plate and are used as actuators in the control scheme In this study, the fully coupled acoustic–plate interaction equations are solved using time‐dependent Green’s function techniques, where a time‐varying mean air density is considered The effects of this variation on the transmission of sound and on the stability of the filtered‐x LMS adaptive controller are discussed

Tackable Acoustical-Barrier Panel

Abstract: The invention is directed to a tackable/acoustical wall panel having a peripheral frame including a top rail, a bottom rail, opposed side rails and a dividing rail bisecting the panel into a first cavity and a second cavity. The dividing rail extends at a height where a work surface would be attached to the panel. The first cavity has a substantially rigid first septum mounted therein in order to restrict sound transmission through the panel. The first septum has opposing rigid front and back surfaces. A tackable inner layer is secured to the first septum. The second cavity has a substantially rigid second septum mounted therein in order to restrict sound transmission through the panel. The second septum has opposing rigid front and back surfaces. A decorative cover is secured to the frame and extends over the first cavity and the second cavity.

Sound field of a baffled piston source covered by a porous medium layer

Abstract: Two models for the prediction of sound transmission through a thick layer of material which lies on a horizontal baffle are presented. These models are a preliminary investigation of a method for the acoustical and physical characterizations of porous materials. The acoustic source is assumed to be a circular, baffled piston source mounted under a layer of porous material. The sound is transmitted through the porous layer to the semi‐infinite half‐space above the layer. The models are used to calculate the transfer function between the volume velocity of the source and the sound pressure above the porous material. The first model is based on the integral method in which appropriate Green’s functions are used to describe the sound field, and on a collocation procedure. The second model uses a method of decomposition of the sound field into cylindrical waves. The numerical results of the two models are in good agreement. A significant sensitivity of the transmitted sound field to the material’s physical cha...

A Model for Sound Absorption by and Sound Transmission Through Limp Fibrous Layers

Abstract: In recent tests it was found that the measured surface normal impedance and transmission loss of limp, fibrous materials could be predicted more accurately when using an elastic porous material model rather than a rigid porous material model: i.e., the motion of the solid phase was found to be acoustically significant. However, it was noted that if the frame stiffness was set to too small a value in the elastic porous model, the boundary value problem that must be solved to yield the surface impedance or transmission coefficient becomes singular. Thus it was of interest to develop a porous material model in which it is assumed from the beginning that the solid phase may move, but that it has no bulk stiffness. Under these circumstances, the Biot model for elastic porous materials may be simplified to yield a single second‐order wave equation governing the propagation of a single wave type in the limp porous material. The solutions to that wave equation in combination with appropriate boundary conditions m...

Horn-shaped piezoelectric ceramic speaker

Abstract: PURPOSE:To provide the wide-band horn-shaped piezoelectric ceramic speaker, which unnecessitates a power amplifier, by coupling a spiral or zig-zag bent sound transmission path to the piezoelectric ceramic speaker using the thin plate of a polymer compound reinforced with inorganic fibers. CONSTITUTION:Concerning a horn-shaped piezoelectric ceramic speaker 1, a lid plate 3 is adhered to a casing 2, the peripheral edge part of a diaphragm 4 is adhered to the lid plate 3, and piezoelectric ceramic 5 is adhered to the diaphragm 4. Concerning the casing 2, a standing wall 7 is formed in a spiral shape to be gradually widened and to gradually enlarge a cross-sectional area with a position 6a of a sound hole 6 bored on the lid plate 3 as a center, and a helical sound transmission groove 8 is formed by the use of the standing wall 7. Whether resistance or environment resistance is improved, faults are hardly generated by a temperature or rainwater, and this speaker is effective when being installed outside as an interphone. On the other hand, any fault caused by magnetism leakage is not generated. Further, since an electric impedance is high, the volume of sound can be increased without requiring any power amplifier, the degree of freedom in designing is improved, and the speaker is easily miniaturized.

Sound transmission device

Abstract: PURPOSE: To provide a sound transmission device which can transmit sound to an aimed listener alone. CONSTITUTION: By mutually shifting phases of aural signals to be supplies to individual speakers 36 to form synthesis sound waves whose surface wavefronts 104 are concave on the side of sound collecting region 100 whereas convex on the side of nondirectional speakers 36, the surface wave front 104 gradually become small and the synthesis sound waves converge to the region 100 by adjusting phase differences among respective aural signals. Then, the amplitude of the aural signal to be fed to each speaker 36 is controlled so that the sound pressure of the sound emitted from each speaker 36 is of a hearing level or lower. Since the synthesis sound waves are formed by superposing the sound waves emitted from each speaker 36, the sound pressure of the sound converged to the region 100 is of the hearing level or higher.

Active control of aircraft cabin noise

Abstract: Aircraft cabin noise control in the past has relief heavily on improving sidewall attenuation by passive ‘‘add‐on’’ treatments. The conventional passive methods, such as adding mass, damping, or acoustic absorption, etc., not only impose a stiff weight penalty, they are also ineffective in improving the low‐frequency sound transmission loss of an aircraft fuselage sidewall. Active control of sound inside aircraft cabins has been the focus of research in recent years and has shown considerable promise. Laboratory and in‐flight tests of prototype active control systems for tonal noise reduction using secondary speakers have demonstrated the feasibility of active noise control (ANC) in aircraft cabins. In recent years active structural acoustic control (ASAC) has also been applied to aircraft fuselage structures in controlling low‐ to mid‐frequency structural sound radiation. In the ASAC technique, control forces are applied directly to the vibrating structure by actuators (such as piezoelectric transducers)...