Showing papers on "Sound power published in 1984"

Acoustic nonlinearities and power losses at orifices

Abstract: Acoustic power losses occur when high-amplitude sound waves impinge on an orifice in the absence of mean flow. Described is a simple theoretical model of these losses, in which a harmonic, linear acoustic field is coupled to a nonlinear hydrodynamic flowfield at the orifice. Experimental and theoretical data on power losses at orifices with both pc and flanged acoustic terminations are compared, and fairly good agreement is noted. The structure of the flowfield in the neighborhood of the orifice is broadly described and some quantitative comparisons are made between the measured translational velocity of the ring vortices shed from both sides of the orifice and theoretical predictions. Again, the theory is seen to give generally reasonable results.

On the Absorption of Sound by Turbulence and Other Hydrodynamic Flows

Abstract: The dissipation of acoustic energy which occurs when sound generates vorticity at the boundaries of a fluid or propagates across a field of turbulence is examined. Vorticity generation occurs typically during scattering or diffraction by surfaces with corners or edges, and an understanding of the consequent attenuation is important in the design of mufflers and other devices used for suppressing acoustic and mechanical vibrations. The rate of dissipation is generally a nonlinear function of the acoustic intensity, but becomes linear and significantly greater in the presence of a mean flow.

Active Impedance Control for One-Dimensional Sound

Abstract: Generalizing the concept of active sound absorption, a system for active impedance control has been developed, so far for plane waves at normal incidence. The active reflector is a loudspeaker driven by the incident sound wave. Its feeding signal is derived from a “wave separator” with two microphones splitting up the standing wave field into incident and reflected wave. This system permits easy control of the reflection coefficient and eliminates feedback instability. Arbitrary reflection coefficients between almost 0 and about 1.5 have been realized in the frequency range from below 100 Hz to more than 800 Hz.

Attenuation of sound waves

Abstract: An active sound control system is described in which allowance is made in a relatively uncomplicated circuit for acoustic coupling between a sound generating system for generating a cancelling sound wave and a detector for sensing a sound wave to be cancelled Unwanted sound from a source is detected by a microphone and cancelled by sound from a speaker connected by way of an amplifier to the microphone The amplifier has a feedback processing system with a transfer function which takes account of acoustic feedback between the speaker and the microphone in deriving, with the amplifier, a signal to drive the speaker

Methods for using a noninvasive technique for estimating glottal functions from oral measurements

Abstract: A noninvasive technique is used to make acoustic and aerodynamic recordings in an ongoing study whose goal is the objective assessment of vocal function in normal and dysphonic speakers. Intraoral pressure, oral volume velocity (flow), and radiated sound pressure are recorded for strings of repeated productions of the syllable /pae/. A high time resolution pneumothachograph is used to record flow [M. Rothenberg, J. Acoust. Soc. Am. 53, 1632–1645 (1973)]. Transglottal air pressure, glottal air flow, and sound power for the vowel are estimated from the oral measurements, and glottal resistance and vocal efficiency are calculated. Initial results suggest that production mode (smooth versus interrupted) and rate (slow versus fast) may affect the reliability of the aerodynamic measures. An interaction between production mode and rate can result in unreliable pressures on one hand and unreliable flows on the other. Results from a separate, methodological study illustrate the importance of control over productio...

Apparatus for determining the weight per unit area of sheet-like material

Abstract: The invention relates to an apparatus for dynamically determining the local weight per unit area of sheet-like material, for example, paper, in which the sheet-like material is exposed to sound waves from a sound transmitter. The portion of sound transmitted and/or reflected by the sheet-like material is measured by aid of a receiver and the weight per unit area determined from the measuring signal. In order to avoid disturbances of the measuring signal due to superimposed sound waves and in order to obtain high local resolution even in the case of quickly moving material to be measured, the transmitter, material to be measured and possibly the receiver as well are arranged on a slant relative to each other in such a way that the portions of sound reflected on these elements are faded out of the path of rays between the transmitter and the receiver. Means are additionally provided to prevent the faded out portions of sound from returning to the path of rays between the transmitter and the receiver.

Method of improving the acoustics of a hall

Abstract: The invention relates to a method to improve the acoustics of a room, preferably a hall, having a relatively minor space (10) from which sound waves, chiefly emanating from a musical instrument, and a relatively larger audience space (12), the outgoing sound waves being re-emitted via an amplifier device comprising a sounding board (20, 22) united with an electromagnet (26), an amplifier (21) and a microphone connected therewith, which device receives impulses from the sound source (14). The sound board (20, 22) and the electromagnet (26) form part of each of a plurality of wall elements (16) of such area and location in the audience space (12) that the sounding boards transmit to the listener a mixture of sound waves directly reflected from the sound source (14) and sound waves indirectly emanating from the amplifier device.

A study on the time constant for an impulse sound level meter

Abstract: Some experiments on the loudness of impact sound were carried out, where the modelimpact sounds based on the actual ones were used as test stimuli. From these experiments, it is clarified that the reading of the sound pressure level through a circuit witha certain time constant can well describe the loudness of impact sounds than its soundenergy does. The values of the time constant of exponential averaging circuit are investigated, accordingly. As the results of this study, a sound level meter with two exponentialaveraging circuits, one of which has5ms rise time constant and250ms decay timeconstant, and the other has125ms rise time constant and250ms decay time constant, shows a good agreement with loudness of a single or repeated impact sounds in the same way as in the loudness of steady sound.

Vane Stagger Angle and Camber Effects in Fan Noise Generation

Abstract: The problem of sound generated by the interaction of velocity disturbances with stator vanes in an annular duct is considered theoretically. The duct carries a uniform subsonic main flow and is assumed to be anechoic. In this problem it seems consistent to model the vanes by flat plates parallel to the duct axis. However, this modeling may yield an unrealistically low acoustic power. In the present paper, a nonplanar lifting surface approximation of the vanes shows that at frequencies prevailing in current turbofans even a small vane inclination significantly affects the sound generation process. The lower the circumferential periodicity \m\ of the cut-on sound field, the more pronounced are the acoustic effects of vane stagger angle and camber. Calculations for a typical example of a turbof an stator show at \m\ = 1 a rise of 23 dB in upstream acoustic power when the stagger angle is increased from 0 to 15 deg. Furthermore, even at \m\ - 16 there is still a rise of 5 dB. Besides the acoustic power, the modal distribution of the sound field is very sensitive to vane camber and stagger angle.

Apparatus for observing sound field of ultrasonic wave

Abstract: An apparatus for observing a sound field of an ultrasonic wave, including a first unit which determines characteristic values (B/A).) of a medium at each point of a predetermined region by an ultrasonic wave having a sound field of an arbitrary form and a second unit (18) which displays an output of the first unit as two-dimensional or three-dimensional distribution (20) in the predetermined region, enabling control of the form of the sound field (16) of the ultrasonic wave.

Characteristics of plasma jet sound. Investigation on welding arc sound. Report 8.

Abstract: The sound of argon plasma jet was measured in order to clarify its characteristics.The characteristics of plasma jet sound depends on the arc current, working gas flow rate and its supplying method. The sound intensity W is shown as a function of the jet velocity v (W ∞ υ6). The sound has a very wide band frequency state that means nearly white noise, and has a peak at an angle of 30°-45° for the jet axis on the directivity.

Research on a Noise Control Device : 1st Report, Fundamental Principle of the Device

Abstract: This study is concerned with a newly developed facility for controlling noise propagation and thereby producing a wide region of reduced sound power, which is expected to be effective to alleviate railroad noise, highway noise, machine noise etc.. The mechanism of noise reduction by this device is destructive sound wave interference between refractive sound waves propagating through multiple passages of different lengths eqipped with the device and direct propagation sound waves. In this paper, the structure and principle of the facility are described and the technical data for practical application are collected.

Welding state monitoring method

Abstract: PURPOSE:To prevent a welding quality from being deteriorated, by comparing a sound pressure level of an acoustic signal inputted at the time of welding, with a sound pressure level of an acoustic signal stored at the time of a stable welding, and deciding whether a welding state is good or not, in accordance with a difference of the sound pressure levels. CONSTITUTION:An acoustic electric signal from a microphone 13 inputting and detecting an arc sound generated from a weld zone 12a of a torch 11 is supplied to band pass filters 15a-15c through an amplifier 14, and the acoustic signal passing through is supplied to a comparator 17 through a sound pressure level meter 16. The comparator 17 compares a sound pressure value or a sound pressure variation value of the inputted acoustic signal, with a reference sound pressure value or an allowable sound pressure variation value stored in advance, decides whether the welding state is good or not in accordance with a difference of said comparison, and a result of decision is displayed on a display device 18 and an alarm device 19. In this way, even in case when a shielding abnormality is generated in the weld zone, the deterioration of a welding quality can be prevented.

Calculation of radiated noise from cylinder block using finite element model

Abstract: The work described in this paper was undertaken as part of a program aimed at predicting engine noise and vibration characteristics at the design stage. Initially, operating engine test and artificial excitation test were carried out with a 4-cylinder, 1500 cc gasoline engine. Through these tests, radiated noise and vibration characteristics of a cylinder block were investigated and noise controlling parameters, such as radiation efficiency, forcing functions and modal damping were examined. Finally, surface response level and radiated noise from the cylinder block were calculated using finite element model by combining noise controlling parameters obtained by the tests. As a result, there was a good correlation between calculated and experimental sound power. The technique presented in this paper is thought to be applicable to predict sound power at the design stage for practical purposes. (Author/TRRL)

Method and apparatus for sound track reproduction

Abstract: A method and apparatus is disclosed for the reproduction of a sound signal recorded on a variable density optical sound track negative, in which the amount of light transmitted through the sound track is related to its exposure by a predetermined relationship Light transmitted through the sound track is transduced to an electrical signal having a magnitude which varies in accordance with the amount of transmitted light, and this signal is operated on by a function which is substantially equivalent to the inverse of the predetermined relationship to produce an output signal which directly corresponds to the exposure of the sound track An adjustment mechanism is provided to eliminate distortion and to enable the production of an accurate output signal even when the relationship between the light transmission and exposure of the sound track is unknown The prior art requirement of producing a print from the negative, with exacting and sometimes unknown characteristics, is eliminated by the use of a convenient electrical circuit

Investigating method of state in tube utilizing reflected sound wave

Abstract: PURPOSE:To investigate the state in a tube quantitatively and qualitatively by providing a sound wave transmitter and a sound wave receiver at one terminal of the tube, and irradiating sound wave pulses and measuring their reflected wave. CONSTITUTION:The sound wave pulse signal generated by a signal generating device 1 is irradiated int the tube 6 form a cone speaker 3 installed at the tube end, and then its reflected wave is obtained from positions which vary in in-tube hollow sectional area, e.g. break position A, foreign matter clogging position B, joint part C, and the other end D where the speaker 3 is not installed. This reflected wave is received by an electret microphone 4 and stored 2. The distances to the positions A, B, C, and D are calculated from time periods up to when reflected waves from the positions A, B, C, and D are received and the propagation speed in the sound wave in the tube. Further, the phase of the irradiated wave is compared with the phase of the reflected waves to decide on whether the in-tube hollow sectional area at each reflected wave generation position is large or small, and the amplitudes of those reflected waves are measured to estimate variation in in-tube hollow sectional area.

Experimental Investigation of Rocket Motor Flow-Turning Acoustic Losses.

Abstract: : Results are presented of an experimental investigation of the 'flow-turning' losses associated with the injection of steady lateral flow into a rectangular duct containing longitudinal acoustic waves. Test results show the flow-turning process absorbs sound. A one-dimensional model was derived that seriously underpredicted the measured acoustic energy losses. Two-dimensional effects in the form of redistribution of the sound pressure due to refraction by the injected mean flow velocity gradients were found to be important. Measurements showed the refraction process to increase the sound pressure at the walls thereby increasing the local wall absorption. Analysis of the data indicates that part of the flow-turning absorption process takes place at the finite admittance side walls and part within the field interior. Most of the sound absorption appears to take place within the fluid interior in support of Culick's ideas, but final interpretation of the data requires the development of a two-dimensional model of the flow-turning process. The identification of the refraction process in new and may have important applications to other rocket motor stability calculations. Key concepts include sound absorption, sound attenuation, sound flow interaction, sound flow energy exchange, flow-turning acoustic losses, and combustion instability.

An Improved Shape for Hermetic Compressor Housings

Abstract: An improved acoustic design for a hermetic compressor shell has been developed. The entire shell'surface is described by a single mathematical expression which insures that there are no discontinuities in either the surface or its curvature. The curvature of the improved housing is maximized within the geometric constraints of the size of the interior pumping mechanism and the specified maximum outside dimensions. The resulting housing, in the case of a small refrigeration compressor, has natural frequenices about one octave higher than exist in conventional housings. These higher resonant frequencies coupled with proper acoustic design of the rest of the compressor can result in significantly lower sound power levels.