(M. Sc.) A survey was undertaken to investigate the occurrence of spontane- ous acoustic emissions from the human ear in a sample of 80 people grouped according to age and sex. A further group of 20 patients attending a tinnitus clinic were also tested. Fourteen ears from the first group and three ears in the tinnitus group were found to produce tonal emissions. Only one of these was found to have any objective correlation with subjective tinnitus. As in most previous studies normal hearing appears to be a necessary but not sufficient condition for the occurrence of these acoustic emissions. In gen- eral no pattern of occurrence was found between the age or sex of the sub- jects.

Thesis Advisor: Dr. A.M. Martin

Finite Element Modeling and Measurement of a Rotor Supported in Four Bearings [43.40.At]--D. Fitzgerald, Institute of Sound and Fi- bration Research, University of Southampton, England, 1982 (M. Sc.) The vibrations of a rotor supported on two fluid journal bearings, one ball, and one roller bearing are investigated. This is achieved using the Finite Ele- ment Package Pafec 75 for the theory, a transient test technique for mobility measurements on the stationary shaft, and both power spectral density and shaft rundown measurements on the rotating shaft. Two finite element models were constructed, the first being comprised of a few simple beam elements, and the second of approximately 400 isoparametric brick ele- ments. The results from these two models showed that the free end of the

shaft vibrated significantly more than the rest of the shaft. Mobilities were also calculated and found to be similar to the measured ones when using bearing stiffness of approximately 10 7 . It was also shown experimentally that the bearing stiffness really represented the bearing housings and not the bearings themselves. From the power spectral density and shaft rundown measurements it was seen that the electric motor driving the oil pump caused some shaft vibration. Also, some of the resonant frequencies corre- spond to those from the Finite Element analysis.

Thesis Advisor: Dr. M. Petyt

To Compare the Vibration Characteristics and Force Paths of Two Identical Gearbox Casings Cast in Different Materials [43.40.At, 43.50.Gf]--K. Periyathamy, Institute of Sound and Fibration Research, University of Southampton, England, 1982 (M. Sc.) The total overall noise produced by an automobile may be due to a number of different noise sources. Much research has been carried out to reduce the noise of the

engine power unit and the aerodynamic noise sources, leaving in many cases the transmission noise predominant. In a study sponsored by the British government to demonstrate that a heavy goods vehicle of noise level 80 dB (A) was feasible, it was considered that gear box radiated noise could be controlled by increasing the mass of the casing. To this end the standard aluminum casing was replaced by one in iron. However, overall noise radi- ation remained basically the same. A study was undertaken to examine the possibility of reducing the gear box noise by manufacturing the gear box housing in iron instead of aluminium alloy. Two identical gear boxes were cast, one in iron, and the other in aluminum. Both gear boxes were tested under static and running conditions to analyze their surface vibration at different gear ratios and a simple mathematical analysis was made to pre- dict the expectations on the housing deformations. From the analysis of the running gear box noise and vibration results and the static test results, it is concluded that by casting the gear box housing in iron, only a nominal reduction in noise can be achieved compared with aluminum housing.

Thesis Advisor: Mr. E. C. Grover

Effect of Gloves on the Transmission of Vibration to the Hand

[43.40.Tm, 43.40.At]--S. J. Viiion, Institute of Sound and Vibration Re- search, University of Southampton, United Kingdom, 1982 (M. Sc.) A proce- dure for predicting the transmission of vibration through gloves for vertical direction in the 10- to 500-Hz frequency range has been devised. The glove transfer function and the mechanical hand-arm point impedance, corrected for the mass of handle, have been measured for several subjects using a simple fiat handle controlling the push force. From estimates of the proper- ties of glove material and the measured point mechanical hand-arm impe- dances, the glove transfer functions were predicted. Rubber material used in this study was found to be effective for frequencies between 40 and 150 Hz depending on the subject. There was a slight amplification below these fre-

quencies. A large variation between subjects for the measurements oftrans- missibilities and point mechanical impedances of the hand was noticed. Finally, the effects on the glove transfer functions of varying stiffness and damping were investigated.

Digital Acoustic Intensity Method in Petrol I.C. Engine Noise Stu- dies [43.50.Ba]--T. Abe, Institute of Sound and I•ibration Research, Uni- versity of Southampton, United Kingdom, 1982 (M.S.) Acoustic intensity is defined as the net acoustic energy flow through unit area or the product of instantaneous pressure and particle velocity. It is considered to be the most desirable quantity for the estimation of the acoustic power of a source. Before the analysis of engine noise, a preliminary study was carried out to examine the nature of the engine noise signature (4-cylinder, 4-stroke petrol engine). The inherent errors of intensity measurement and digital process- ing were examined for this case. Then a computer program was established and a series of measurements made on a running petrol engine in a semiane- choic test chamber. The intensity results were studied on a 1/3-octave fre- quency basis for acoustic power calculation, calculation of the contribution of each component (source identification), and comparisons were made with other methods. Although the acoustic power balance for each method agreed very closely, when used to calculate the intensity and sound pressure level at a distance (up to 1 m) from the engine it was found that even at 1 m the intensity level at high frequency was considerably lower than the mean square pressure value indicated. An investigation of the intensity field as it changed with distance from the engine was made. This showed that at fre- quencies below 250 Hz the measured intensity was higher than the p2/c intensity while at high frequencies it was lower.

Thesis Advisor: Dr. D. Anderton

Accuracy of Constrained Mode Method in Component Mode Syn- thesis Techniques [43.40.At]•Z. W. Wang, Institute of Sound and Vi- bration Research, University of Southampton, United Kingdom, 1982 (M. Sc.) Component mode synthesis techniques treat a complex structure as an assemblage of distinct substructures. The constrained mode method is one of them and has very good convergence. The method employs two forms of generalized coordinates and the other substructure normal-mode generalized coordinates. The coordinate transformation matrices that are employed in obtaining the system mass and stiffness matrices from the mass and stiffness matrices of the substructures are based on the definition of

constraint modes, substructure modes, and the requirement of compatibi- lity along substructure boundaries. The second form of modes, "substruc- ture normal modes," are investigated for their contribution to the system modes. It is shown that the constrained mode method has even better con-

vergence if all the substructure normal modes are rearranged according to the descending order of their eigenvalues. The illustrations show that the number of accurate system modes N is given by N--CM, where M is the number of substructure normal modes used and C a constant whose value

depends upon the type of structure. IffN is the highest system frequency of interest, then all substructural normal modes with frequencies less than should be used where fM > CfN. Again the constant C' depends upon the type of structure.

Thesis Advisor: Dr. M. Petyt

Applications of Recurslye Parametric Estimation Methods to Vi- brating Systems [43.40.At]--F. J. C. Girard, Institute of Sound and Fi- bration Research, University of Southampton, United Kingdom, 1982 (M. Sc.) The investigation carried out in this thesis concerns a particular type of parametric time domain method in system identification called the "least squares" method. Both time invariant and time variable models are considered and recursive schemes are provided for both of them. The ordi- nary reeursive least square (RLS•time invariant scheme} using an auto- regressive moving average (ARMA} model is tested on the estimation of transfer functions involved in a feedback closed loop system illustrating the general problem of deconvolution. The "windowed" reeursive least squares scheme (WRLS) (time variable scheme) is developed and tested on vibrating systems where the parameters, as well as the structural parameters (natural frequencies and dampings), are estimated, using only swept sine waves in input. The main conclusion is that the time domain (WRLS) approach is at least as efficient as the frequency domain approach for the estffnati0n of

698 J. Acoust. Soc. Am., Vol. 73, No. 2, February 1983 Notes and Briefs 698

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vibrating systems in the case of widely spaced and lightly damped modes. The estimation procedure concerning the feedback analysis has also sub- stantiated the satisfactory behavior of the least squares scheme and has provided the basic knowledge for a possible deconvolution procedure. Thesis Advisor: Dr. J. K. Hammond

Spectral Distortion in (he Nonlinear Propagation of Jet Noise in the Atmosphere [43.50.Nm, 43.50. Lj, 43.25.Cb]--¾. H. Berthelot, In- stitute of Sound and Vibration Research, University of Southampton, United Kingdom, 1982 (M. Sc.) According to the theory of nonlinear noise propaga- tion, the nonlinear spectral distortion of jet noise propagating in the atmo- sphere can be expressed in terms of certain high-order statistics of the signal. The main objective of this study is to process on the computer of the Data Analysis Centre some recorded aircraft noise data, in order to assess the statistical properties of these flyover signals. A special program has been written which performs the required analysis. Three different flyover test si• of a•Wo-engined BAC 1-11 aircraft flying between 200 and 600 m

/altitude, have been analyzed on the computer (PDP 11/50). The results show that a statistical model based on Gaussian statistics agrees up to a certain ext, ent with the experimental data, so that a prediction scheme can be derived in order to predict an estimate of nonlinear spectral distortion in jet noise propagation.

Thesis Advisor: Dr. C. L. Murfey.

An Investigation on Design and Performance of Low-Frequency Panel Absorbers [43.55.Ev]--M. H. Taghavi-Nejad, Institute of Sound and Vibration Research, University of Southampton, United Kingdom, 1982 (M. Sc.) The aim of this project was to establish practical guidelines for the low-frequency panel absorbers and, in this context, to evaluate and consoli- date the informations gained in previous experimental and theoretical works by various researchers. In the present work, therefore, there have been two interconnected trends. One has been the assessment of the ideas

expressed by other authors and the other has been a mainly experimental approach to lay out new techniques in tuning of absorbers, in verifying different materials' characteristics, when used in absorbers, and in collect- ing the practical details necessary for a useful design. The latter also includ- ed a study of the effect of coupling of absorbers to rooms as well as colora- tion and structural damping. There is no claim, however, that the above objectives have been thoroughly fulfilled. There still exists a multitude of factors which should be taken into account. Many of these factors are still unknown; one would hope that during the process of identifying them, better and more precise experimental techniques will be developed.

Thesis Advisor: Professor P. E. Doak

several directions. A theoretical model is developed for a structure undergo- ing translational and rotational motion, which takes into account not only the structural impedance matrix but also the physical properties of the var- ious components added to it, i.e., the masses and inertias and the coupling of transducers to the structure as well as the force gauge and aecelerometer (or impedance head) cross sensitivities. The results of extensive theoretical and experimental analysis are given and commented upon in the case of semi- infinite beam model which demonstrates the applicability of the theoretical investigation. Moreover, some results are presented concerning an attempt to measure the force gauge bending moment arid aecelerometer rotational sensitivities.

Thesis Advisor: Dr. R. C. White

A Feasibility Study of Active Noise Cancellation of Low-Frequen- cy Sound Inside Vehicle Cabs [43.50.Gf]--T. S. Berge, Institute of Sound and V/brat/on Research, University o/Southampton, United King- dom, 1982 (M. Sc.) A feasibility study of the possibility of active control of a vehicle cab interior noise has been carried out. With optimalization of a feedback control system, approximately 15-dB reduction at about 30 Hz has been achieved for a stationary vehicle at idle engine speed. A bucket- brigade device has been designed as a compensating network. The system did not give broadband cancellation due to limitation in the feedback loop system, but with improvements, the system will give considerable cancella- tion from 20 to about 200 Hz. At 30 Hz the cancellation zone was large enough to cover both the driver and passenger seat. The main problem with the feedback system was the lack of stability when a change in the system conditions occurred. Measurements of the noise spectra show a strong cor- relation between the harmonics of the fundamental firing frequency of the engine and the cab pressure signal. The cab noise is mainly airborne noise transmitted through the cab floor structure. Due to the periodicity of the cab noise signal, an adaptive active feedforward system would be the opti- mal system from a commercial point of view. Digital filtering would in- crease accuracy and performance of the system. Thesis Advisor: Professor A. Krokstad

Technical reports [43.10.Os]

The following technical reports may be obtained from the National Technical Information Service, Springfield, VA 22151 under the order numbers indicated, unless otherv•ise noted.

Residual Spectral Analysis Applied to the Multiple Input/Output Problem [43.85.Kr, 43.85.Ta]--T. V. Nguyen, Institute of Sound and Vi- bration Research, Uniuersity of Southampton, United Kingdom, 1982 (M. Sc.) In many engineering problems it is often very important to identify the nature of multiple acoustic or vibration sources and the significance of their separate and combined effects at a given point. Residual (conditioned) spectral analysis offers promise as a useful analysis tool for complex prob- lems and the work reported in this thesis covers four aspects of multi-input system analysis. These are (i) the presentation of a brief summary of the theory for multi-input/output problems involving stationary random pro- cesses and discussion of extensions to cases where the processes are not random, (ii) the development of easily usable software to perform residual spectral analysis on the I.S.V.R. PDP 11-50 computer, (i/i) the investigation of sources of errror, (iv) the application of the method to experimental data to highlight practical difficulties.

Thesis Advisor: Dr. J. K. Hammond

The Effect of Exciter Coupling and Transducers' Characteristics on Measured Structural Frequency Response [43.40.^t]--F. G. Pla, Institute of Sound and Vibration Research, Uniuersity of Southampton, United Kingdom, 1982 (M. Sc.) This study deals with the problems arising when measuring the frequency response of a structure exhibiting motion in

Community Noise Assessment Manual: Acoustical Survey of a Community [43.50.Sv]--I•ryle Research, El Segundo, C,4 and *Environ- mental Protection ,4gency, I•rashington, DC,' Jul 81, 319 pp. (Microfiche only). The report was prepared by EPA, Office of Noise Abatement and Control, in support of its function to provide technical assistance to com- munities. It is one of nine which make up the Community Noise Assessment Manual. The Manual provides a comprehensive and computerized system for assessing the noise problems of a community and then planning a noise control strategy for its abatement. This Manual presents the technical in- struments and guidelines needed by municipal authorities to carry out an initial noise survey. This survey will determine average noise levels and major noise sources for the community as a whole. It can be used in plan- ning noise reduction measures to benefit the entire community or a substan- tial portion thereof. [Order No. PB82-106196.]

Effect of Barriers on Propagstion of Construction Noise [43.50.Gf]--H. S. Gill, Southampton Uniu. (England). Inst. of Sound and Vibration Research, and *National,4eronautics and Space ,4dministration, }Fashington, DC, Dec 80, 103 pp. Comparison of measurements with over 400 separate predictions for wedge-shaped barriers of bare compacted earth shows that Maekawa's thin barrier theory is adequate for predicting A- weighted barrier attenuation for construction noise sources. The mean dis- erepanty between measured and predicted barrier attenuation was 0.5

699 J. Acoust. Soc. Am. 73(2), Feb. 1983; 0001-4966/83/020699-02500.80; ¸ 1983 Acoust. Soc. Am.; Notes and Briefs 699

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