6926475984

Increasing power consumption in recent yeers has led to the uje of larger and mora powerful machines which are. in most cases, sources ot noise. Correjpondingly, there have been increeses in k>w-frequency sources. The current methods employed in controlling low-frequency noise are mainly passive. employing bulky insulating, as wełl as absorptive, materiał* to stop the noise transmitting from source to listener. The hardware is expensive and relatively inefficient in raducing low frequency noise. This is an area where active attenuators are particularly useful due to their ability to operate at Iow frequencies. Considerable work has been carried out to apply active attenuators to the Controls of transformer noise. engine exhaust noise. 8nd duet borne noise.

84-1765

Noiae of Rotating Yam in Textile Machines

F. Angrilli and V. Cossalter

Istituto di Meccanica Applicata alle Macchine, Fac-olta di Ingegneria. Universita di Padova. Via Venezia, 1-35100 Padova. Italy. Noise Control Engrg. J.. 22 (2). pp 48-53 (Mar/Apr 1984) 7 figs. 11 refs

Key Words: Yarns, Textile looms. Industrial facilities. Noise generation

An experimental and theoretical study of sound radiation from a rotating yarn in textffe machines is presented. The mathematical model is developed from the basie aoousticsl equations of the sound field radiated by a time varying point force in arbitrary motion. derived in a convenient form by Lowson. Ex per im en tal results obtained with a single rotating yarn show reesonable agreen.t.nt for trends and good agree-ment for peek levels and frequencies. The importance on the pressure level of the direction of the observer with respect to the ballon axis direction is stressed.

84-1766

Industrial Noise Control: Architectural and Environ-mental Aspects. 1975 • January, 1984 (Gtationa from the International Information Seryice for the Phyacs and Engineennf Communities Data Base)

NTIS. Springfield. VA. 174 pp (Jan 1984) PB84-857408

Key Words: Industrial facilities. Noise reduction. Bibliog-raphies

This btoliography contains 235 cłtations concerning architectural and engineering acoustics associsted with noise

control in industrial environments. Important sources of industrial noise and the level of exposure of workers to noise are examined. Methods of active attenuation of noise; i.e., the cancelling of noise from a source by the addłtion of further noise, including both absorptive and non-absorptive methods are presented.

84-1767

On the Acoustic Pressure at the Surface of Circular Radiatora (Uber den Schalldruck an der OberflMche von kreisfórmigen Strahlera)

H. Fleischer

Institut f. Mechanik, Fachbereich Luft- und Raum-fahrt, Hochschule der Bendeswehr Munchen, Acus-tica, 54 (3). pp 161-171 (Jan 1984) 10 figs, 19 refs (In German)

Key Words: Acoustic excitation

The acoustic pressure on the surface of planar circular struc-tures, fitted in an infinitely large baffle. is calculated accord-ing to the Huygens-Rayleigh principia. A few simple non-axisymmetric vibrational-mode shapes are considered. The necessary integration is done numerically with the aid of a desk Computer.

84-1768

Time Spread of Acoustic Signals Reflecting from a Fixed Rough Boundary

M.H. Brill. X. Zabal.and S.L. Adams Science Applications, Inc., 1710 Goodridge Dr., McLean, VA 22102. J. Acoust. Soc. Amer.. 75 (4). pp 1062-1070 (Apr 1984) 10 figs. 13 refs

Key Words: Sound waves, Wave propagation, Wava reflaction

The time spreading of a u>hericat-wave impulsa of acoustic power reflecting from a not-too-rough fixed boundary (such as an ocean bot tom) is computed using a simple geometric-acoustic model. In the model a ray reflects specularly from each boundary facet, and arrives at the recehrer if, and only if, the poshion and slope of the facet provide the requisite specular peth. In this way, the probability of reception of a ray from a particular facet is tiad to the slope distribution of the reflecting boundary (assuming the depth is constant). A generał expression for tima spread is derived, and computed time spreads are presented for particular source/receiver geometries.