István L. Vér

Impact Noise Isolation of Composite Floors

This paper describes a procedure for calculating the impact‐noise level of a bare stiff structural floor when excited with a standard tapping machine. Calculations are also given for the improvement in impact noise isolation achieved by adding to the structural floor (a) an elastic surface layer, (b) a locally reacting floating floor, and (c) a resonantly reacting floating floor.

Low-noise chambers for auditory research.

The experimental work of the Eaton–Peabody Laboratory of Auditory Physiology requires chambers unusually free of ambient acoustic, vibratory, and electric noise, so that small mechanical or electric signals in response to low‐level sounds can be measured. This paper deals with the problems that arose in setting of criteria, the design, and the construction of such chambers, and reports on the evaluation of their performance. The ambient acoustic noise is well below the human threshold of hearing even with the ventilation system operating. The noise reduction between the control rooms and the chambers is almost 80 dB at 250 Hz and more than 90 dB above 500 Hz. The octave‐band ambient vibration acceleration level at the experimental tables in the chambers is below −120 dB re lg.Subject Classification: 55.40; 65.10.

Field Study of Sound Radiation by Power Transformers

Information needed for the acoustic design of power transformer installations required to meet specific property line noise criteria was obtained through a study, in the field, of 40 in-service power transformers. This paper reports on the unique method of data acquisition and of data reduction; summarizes the information gained by the analyses of the nearfield and farfield noise measurements regarding (1) the tonal composition of the core noise, (2) the circumferential statistics of the sound radiation pattern, (3) the variation of the noise level with distance, and (4) the relation between noise levels measured at NEMA positions and in the far field; and recommends improvements in the standard transformer noise measurement method that would yield information about the tonal characteristics of the transformer noise.

Some accoustical characteristics of a crossing‐jet noise source

The acoustical characteristics of a high‐intensity omnidirectional sound source used in acoustical scale‐model experiments are described in this paper.Subject Classification: 50.30; 55.10.

Anechoic wedge design and development/anechoic chamber qualification testing

The initial research conducted at Harvard University’s Electro Acoustic Laboratory for the development of the anechoic chamber will be reviewed in this presentation. These findings, which were originally presented in the Office of Scientific Research and Development National Defense Research Committee Report No. 4190 (OSRD, No. 4190), will be discussed. The research conducted by Leo L. Beranek and his colleagues during WWII established the basic design and construction for anechoic wedges and chambers for years to come. Contemporary design and materials used in anechoic wedge construction have evolved to encompass a variety of room acoustic treatments, to include fiberglass, foam, and metallic wedges. Design and construction of current commercially available chambers and wedges will be reviewed. The second half of the presentation will focus on the development of anechoic and hemianechoic chamber qualification procedures to current ISO and ANSI standards. The use of various sound sources will be discussed...

Using reciprocity to predict aircraft interior noise due to multiple correlated input forces

This paper reports on how to utilize reciprocity to predict aircraft cabin noise due to multiple correlated point forces, such as those acting on engine mounting points. The transfer functions are determined by a reciprocal experiment by measuring, at the force excitation points, the magnitude and phase of the vibration response due to the operation of a point sound source located in the cabin. The experiments reported were carried out on the fuselage of a light aircraft. The methodology, the experimental apparatus, the software, and the test results will be presented and the advantages of the reciprocity method discussed. [Work supported by NASA Langley Research Center.]

Spatial statistics of transformer core noise

The tonal nature of the core noise, the difference in pathlength and the different phasing of the sound radiated from the various tank surfaces result in complex spatial interference patterns which characterize the farfield which can be described only in statistical terms. This paper deals with the consequences of the statistical nature of sound field in regard to: (1) Developing meaningful techniques to measure farfield transformer core noise, (2) predicting the expected value and spatial statistics of the farfield noise on the basis of near/field measurements, and (3) defining meaningful performance evaluation measures to determine the effectiveness of such retrofit noise control measures as barriers and enclosures.

Use of reciprocity in predicting the sound radiation of complex structures

Complex structures such as the fuselage of an aircraft or the body of a car are usually subject to airborne as well as to force excitation. To formulate noise control strategies, it is necessary to know what portion of the interior sound field is due to airborne and what portion to force excitation. A special reciprocity method described in this paper, can be beneficially employed to achieve this desired separation. The paper reports on the theory, the experimental methodology and on a successful application of the reciprocity method to predict the force‐induced sound field in a complex full‐scale structure.

Noise generation by rain on lightweight roofs

Raindrops impacting on the lightweight roofs of buildings, such as performing arts facilities and sports arenas, may generate noise of sufficient intensity to interfere with hearing conditions. This paper identifies the key physical parameters that control the noise generation process and presents an analytical model that permits the prediction of the intensity and spectral distribution of rain‐induced noise.

Power transformer noise emissions

This paper presents the results of an experimental study of the sound radiation of in‐service power transformers in the 20‐MVA to 300‐MVA range. It was found that (1) for transformers in the power range of 20–30 MVA, the 120 Hz tone and for transformers with power rating above 30 MVA the 240 and 360 Hz tones control the A‐weighted noise emissions; (2) changing the standard transformer noise rating procedure to include measurement of the first four tones at NEMA positions would increase the accuracy of farfield noise predictions; (3) the circumferential variation of both the tone and A‐weighted levels, measured at 50 and 100 ft, approximate a Gaussian distribution with ω =4 dB for each of the first four transformer tones and ω =1.75 dB for the A‐weighted level; (4) the relation between the level measured at NEMA positions, LN, and at distance d, Ld, is Ld=LN−20 log (d) +10 log(S) −8, where d is the distance in ft. and S is the area of the vertical tank surface in ft.2; (5) it was found that changes in ...