INTERNATIONAL SOUND AND VIBRATION DIGEST Volume 1, Number 4 Date: May 5, 1995 Editor-in-Chief: Malcolm J. Crocker, Auburn University, USA Assistant Editor: Yana Sokolova, Auburn University, USA Editorial Board: Duan-shi Chen, Jiao Tong University, Shanghai, CHINA Frank Fahy, ISVR, Southampton University, UK Jean L. Guyader, INSA de Lyon, FRANCE Colin H. Hansen, University of Adelaide, AUSTRALIA Hanno Heller, DLR, Braunschweig, GERMANY Nikolay Ivanov, Baltic State University, St. Petersburg, RUSSIA Finn Jacobsen, Technical University of Denmark, DENMARK G. Krishnappa, Institute for Machinery Research, NRC, CANADA Conny Larsson, Uppsala University, SWEDEN Martin V. Lowson, University of Bristol, UK Leonid M. Lyamshev, Andreev Acoustics Institute, Moscow, RUSSIA Eric Marsh, Penn State University, USA M.L. Munjal, Indian Institute of Science, Bangalore, INDIA David E. Newland, The University of Cambridge, UK Michael P. Norton, University of Western Australia, AUSTRALIA A. Selamet, The University of Michigan, Ann Arbor, USA Andrew F. Seybert, University of Kentucky, Lexington, USA Jan W. Verheij, TNO, Delft, THE NETHERLANDS. Current number of subscribers: 1037 To send a submission to the IS&V DIGEST or to subscribe or unsubscribe, send information by E-mail to yanas@eng.auburn.edu. TODAY'S DIGEST CONTENTS ITEM 1. INTRODUCTION. ITEM 2. OVERVIEW: Research on Active Vibration Control Systems in Slovakia. Past and Present. ITEM 3. PROFESSIONAL SOCIETY: Australian Acoustical Society. ITEM 4. Department of Acoustics, Moscow State University, Russia. ITEM 5. CONFERENCE: Fourth International Congress on Sound and Vibration, St. Petersburg, Russia. ITEM 6. CONFERENCE: Inter-Noise 96, Liverpool, England. ITEM 7. CONFERENCE: 2nd International Conference on Acoustic and Musical Research. ITEM 8. CONFERENCE: The Fourth Session and Advanced Study School on "Acoustical Measurements. Methods and Instrument". ITEM 9. SHORT COURSES: Wayne Tustin Again Teaching Vibration. ITEM 10. READER QUESTION: Architectural Acoustics Simulation. ITEM 11. BOOK REVIEW: "Engineering Vibration" by Daniel J. Inman. ITEM 12. BOOK ANNOUNCEMENT: 3-D Sound for Virtual Reality and Multimedia. ITEM 13. TECHNICAL PAPER: Active Noise Control and Group Delay. ***************************************************************************** ITEM 1. INTRODUCTION. ***************************************************************************** We are pleased to bring you the fourth issue of the DIGEST. ITEM 2 OUR OVERVIEW concerns research in active vibration control in Slovakia. The particular application described is the design of an active vibration control system for the driver's seat of an Earth Moving Vehicle. The professional society featured in this issue is the Australian Acoustical Society (ITEM 3). The acoustics education and research program featured in this issue is the Department of Acoustics in the Faculty of Physics at Moscow State University. Next, preliminary announcements for two conferences to be held in 1996 are included: ITEM 5, the FOURTH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION, St. Petersburg, Russia, 24-28 June, 1996 and ITEM 6, INTER-NOISE 96 to be held in Liverpool, England, 30 July-2 August, 1996. Next are final announcements concerning two conferences to be held very soon in May 1995: ITEM 7 The 2nd INTERNATIONAL CONFERENCE ON ACOUSTICS AND MUSICAL RESEARCH, Ferrara, Italy, 19-21 May 1995 and ITEM 8 THE FOURTH SESSION AND ADVANCED STUDY SCHOOL ON ACOUSTICAL MEASUREMENTS, METHODS AND INSTRUMENTS, Moscow, Russia, 23-25 May, 1995. ITEM 9 concerns a short course offering and ITEM 10 is a reader question concerning architectural acoustics simulation. ITEM 11 is a book review by Eric Marsh of the new book ENGINEERING VIBRATION by Daniel J. Inman, and ITEM 12 is a book announcement concerning 3-D SOUND FOR VIRTUAL REALITY AND MULTIMEDIA by Durand R. Begault. Last but not least (ITEM 13) is the continuation of our TECHNICAL PAPER series on Active Noise Control. In this issue we feature another article by Colin Hansen titled ACTIVE NOISE CONTROL AND GROUP DELAY. We are pleased to inform you that back issues of the ISV Digest are available on the Auburn University Gopher (Academic Areas and Departments-College of Engineering-Department of Mechanical Engineering). We hope that you are finding the ISV DIGEST useful. We should be interested to hear your comments and to receive items for inclusion in the next issue. These should be sent to yanas@eng.auburn.edu. Malcolm J. Crocker Editor-in-Chief ***************************************************************************** ITEM 2. RESEARCH ON ACTIVE VIBRATION CONTROL SYSTEMS IN SLOVAKIA PAST AND PRESENT. ***************************************************************************** George Juraj STEIN, Igor BALLO P a r t 1 Institute of Materials and Machine Mechanics SLOVAK ACADEMY OF SCIENCES Racianska 75 ; P. O. Box.d95 SK-83008 Bratislava, SLOVAK REPUBLIC tel.: +427-378 2965, fax.:+427-372 909 e-mail (INTERNET): ummsste@savba.savba.sk 1. INTRODUCTION: As part of the former Czechoslovakia, the Slovak Republic possessed a well developed industry, agriculture and infrastructure. Among various Research Establishments engaged in fundamental research, the SLOVAK ACADEMY OF SCIENCES has played a major role. The INSTITUTE OF MATERIALS AND MACHINE MECHANICS located in BRATISLAVA has a long history of active vibration control systems research, especially for driver's seats. The aim of this paper is to summarise research results and give an overview of the past research activity on active electro-hydraulic systems. The results were published in condensed form in [12] and in the references appended. It is believed that due to historical circumstances, most of these sources were not readily available. Interested readers are informed of these references and encouraged to contact the authors in cases of interest. These research activities date back to the early seventies, when BALLO and HERRGOT [1] published the results of theoretical and simulational studies of an active vibration control system of the electro-hydraulic type. In those times, digital computers were neither as sophisticated nor as fast and abundant as today. On the other hand there was extensive experience with simulation of dynamic systems and modeling on analogue computers. Good quality analogue computers were available from home industries. This study showed the theoretical feasibility of a 1 DOF electro-hydraulic active vibration control system. 2. FURTHER RESEARCH OF ELECTRO-HYDRAULIC SYSTEMS: Following the above-mentioned paper, another active electro-hydraulic system was designed [2]. At the end of a positionally controlled servo-cylinder situated in the vertical direction a guided platform was mounted, to which a standard driver's seat was fixed. This configuration had been deemed to be fail-safe, i.e. if the supplementary active system failed for any reason whatsoever, the driver would still be protected against adverse vibration by the ordinary seat and would be able to drive the vehicle/machine until it was repaired. A realistic hydraulic servo-cylinder was assumed, approximated by a first order low-pass filter with a cut-off frequency (- 3 dB) of the order of a few Hz. Non-ideal properties of the working fluid were neglected. The feed-forward (compensation) principle was used, the vehicle chassis vertical acceleration being used as the reference signal. An analogue model was built [2] and a simple controller was designed. The controller was essentially a double integrator with a very low cut-off frequency of 0.01 Hz transforming the input acceleration to a control voltage driving the servo-cylinder in such a way as to generate piston rod movement opposite to the simulated chassis vertical excitation. The analogue model was subjected both to constant amplitude harmonic excitation with a linear frequency sweep from 0.1 rad/sec to 10.0 rad/sec, i.e. from 0.015 Hz to 1.5 Hz [2] and to narrow band random excitation in the same frequency band [3]. A hybrid system measuring the ratio of rms accelerations at the load (seat cushion) to that of the simulated vehicle chassis was designed and set up on the analogue computer. It formed a semi-automatic system for the measurement of the modulus of the frequency response function for both harmonic and narrow band random signals. The qualitative simulation results [2] and the more quantitative results [3] with both the swept harmonic excitation and the narrow band random excitation showed that the frequency response function of the active system had a "U" form shape. The vibration transmissibility increased both on the low frequency side (approx. below 0.3 rad/sec, i.e. 0.05 Hz) and on the high frequency side (approx. above 2 rad/s, i.e. 0.3 Hz). There was a usable frequency band approx. between 0.3 rad/sec to 2.0 rad/sec ( 0.05 to 0.3 Hz ) where the modulus of the frequency response function had a flat minimum. The effects at the frequency band margins were attributed to: 1. the cut-off frequency of the hydraulic actuator, which was not able to maintain the proper phase relation above this frequency (the exact opposite motion of the platform to the vehicle chassis); 2. the properties of the double integrator. As the so called perfect integrator could not be used for these purposes, the required double integration had to be performed either by a cascade of two first order low pass filters with a very low cut-off frequency, or a second order critically damped system had to be used [5,6]. Both circuits used for the controller design show a phase deviation from the 180 degrees phase shift required for proper operation as the excitation frequency is tuned from higher frequency towards the cut-off frequency (from right to left on the frequency axis) thus deviating from the required perfect integrator response. As a result, the active system performance deteriorates as low frequencies are approached. This can be eliminated to some extent by the selection of a very low cut-off frequency for the integrator, as in the simulation, but then high grade electronic components are needed for the controller, which becomes susceptible to drifts and static transients. Similar arguments were also used independently by MARGOLIS [13]. The "high-frequency" deterioration of the active system by the "slow" actuator could be compensated to some extent by the use of a compensation signal corresponding to the isolated body acceleration, thus increasing the usable frequency band above 10 rad/s, i.e. to 1 - 2 Hz. 3. EXPERIMENTAL INVESTIGATION OF A DUMMY SYSTEM: The simulation results proved the feasibility of such a compound vibration control system with feedforward control and therefore a full scale dummy was constructed in cooperation with an industrial partner. A standard servo-cylinder used in vibration testing machines was employed, together with matched control electronics, made by a local company. The cylinder was mounted in a horizontal direction and a special linear lever mechanism was used to transform the piston rod movement into vertical movement of the platform. On this platform, a standard driver's seat commonly used in this country was mounted [5-8,11]. The active system was mounted onto a vibration simulator, which consisted of a rugged beam 2 m long pivoted at one side and driven at the other end in the vertical direction by another servo-cylinder. Here the active system was situated. The tangential movement in the vertical direction was supposed to be a good approximation to the required vertical motion in line with the then emerging ISO Standard 7096:82 [16]. The excitation was generated according to the ISO Standard 7096:82 recommendations for various earth moving machine classes [11,16]. The vibration control properties were evaluated according to this Standard as well [11,16]. A computerised measuring system based on a mini-computer equipped with a data accquisition unit in the then current CAMAC Standard was configured [4,9-11]. The vibration acceleration in the vertical direction was measured by commercial piezoelectric accelerometers and charge pre-amplifiers and then sampled in the analogue data accquisition unit. In parallel a "ride-meter" type commercial analogue instrument was used for informative measurements. A sophisticated disk-based, structured programme was written in the Fortran language [9,10]. The electronic controller for processing the reference signal from the simulated vehicle chassis was set up on the analogue computer [6]. In the later stage a similar controller was built from standard passive components and operational amplifiers [11]. 4. EXPERIMENTAL RESULTS: The system vibration control properties as reported in [5-8,11] and summarised in [12] are as follows: 1-ST STAGE: tractor seat type ZT-300, simulated driver's load 75 kg, excitation to third machine class (wheeled loader/tractor) controller designed on an analogue computer [5-7]. seat's damped resonance frequency: 1.3 Hz. IMPROVEMENT by the active system: transmissibility improvement from 2.3 --> 0.4 narrow band vertical acceleration on seat improvement from 0.87 m/s.s --> 0.25 m/s.s, i.e. 3.5-FOLD SEAT value [14] improvement from 53 % --> 15 % 2-ST STAGE: pneumatic seat type KAROSA 281.0, simulated driver's load 75 kg, excitation to second machine class (tractor scraper) controller made from common components. seat's damped resonance frequency: 1.1 Hz. IMPROVEMENT by the active system: transmissibility improvement from 1.1 --> 0.6 narrow band vertical acceleration on seat improvement from 1.03 m/s.s --> 0.34 m/s.s, i.e. 3-FOLD SEAT value [14] improvement from 65 % --> 22 % Also the modulus of the frequency response function for the first stage was determined by the above-mentioned hybrid measuring system in the frequency range 0.5 to 6.0 Hz [6]. The response of the active system only resembled a "U" type curve in good agreement with the simulated results [3]. The curve minimum could be "tuned" to the required frequency of 2.0 Hz, where the vibration excitation Power Spectral Density had its maximum. The modulus of the frequency response of the compound system also exhibited a minimum and then closely followed the response of the passive system as the frequency increased. At lower frequencies, an increase above the value of unity of the passive system frequency response was observed, attributed to the controller behaviour as stipulated by the simulation. A drift of the seat middle position was also observed. 5. CONCLUSIONS: THE MOST IMPORTANT RESULT IS THE THREEFOLD IMPROVEMENT IN THE VIBRATION CONTROL PROPERTIES UNDER RANDOM EXCITATION DUE TO THE INTRODUCTION OF THE COMPENSATION (feed-forward) ACTIVE VIBRATION CONTROL SYSTEM. This enables a marked increase in the allowable exposure time (at fatigue decreased proficiency boundary according to the ISO 2631/1:85 Standard [17]) for the seated driver from approx. 1.5 - 2 hours for the whole working shift ! Of course there is an energy demand associated with the use of this active vibration control system. The active system has to maintain the proper static position and to move all the parts of the system, including the driver's seat with the driver seated up and down. A rough estimation of the required power from the experimetal data gives the requirement of approximately 2.2 kW effective power at 100 bar of fluid pressure [12]. The peak demand is greater but this can be supplied by a suitable hydraulic accumulator. TO CONCLUDE: the results of our research, undertaken in the period from 1970 to 1985, demonstrated by simulation and by measurement on a dummy system the technical feasibility of an electro-hydraulic active vibration control system for driver's seats of earth moving machines. These results were also transfered into Czechoslovak patents and given to an industrial corporation for further economic assesment. 6. REFERENCES: Note: only important references in the native Slovak language and English references are given. [1] Ballo, I. - Hergott, J.; 1974: ANALYSIS OF DYNAMICAL PROPERTIES OF ACTIVE VIBROISOLATING SYSTEMS. (In Slovak) Strojnicky casopis Vol.25 (1974), No.6., pp. 637-645. [2 ] Ballo, I.; 1976: ACTIVE VIBRATION CONTROL SYSTEM WITH EXCITATION SIGNAL COMPENSATION (In Slovak) 2nd Conference on theory of machines and mechanism. Liberec, CSSR, 1976 Proceedings, pp. 335-345. [3] Stein, J. - Ballo, I. - Dalzuffo, J.; 1979: INVESTIGATION OF MODEL OF ACTIVE VIBRATION ISOLATING SYSTEM ON AN ANALOGUE COMPUTER. (Abstract also in Russian). Proceedings of the 12th Conference on Dynamics of Machines, Strbske Pleso, CSSR, April 1979, pp. 465-478. [4] Stein, J. - Tirinda, P. - Chmurny, R.; 1982 ACQUISITION AND PROCESSING OF ANALOGUE SIGNALS BY A MINICOMPUTER EQUIPPED WITH A CAMAC UNIT. (in Slovak) Elektrotechnicky casopis Vol.33 (1982), No.6., pp. 469-477. [5] Ballo, I. - Szuttor, N. - Stein. J.; 1983: INVESTIGATION OF AN OPERATOR SEAT WITH ACTIVE VIBRATION CONTROL SYSTEM. Proceedings of the l4th Conference on Dynamics of Machines, Prague, CSSR, Sept. l983, pp. 23-25. [6] Ballo, I. - Szuttor, N. - Stein, J.; 1984: EXPERIMENTAL RESEARCH OF DYNAMIC PROPERTIES OF THE OPERATOR'S SEAT OF AN EARTH MOVING VEHICLE WITH AN ACTIVE VIBRATION CONTROL SYSTEM. (in Slovak) Strojnicky casopis Vol.35 (1984) No. 1-2, pp. 7-17. [7] Ballo, I. - Stein, J. - Szuttor, N.; 1985: ACTIVE VIBRATION CONTROL SYSTEM FOR OPERATOR'S SEAT FOR EARTH MOVING VEHICLES. In.: K. V. Frolov (Ed.): "Man Under Vibration" Proceedings of the 2nd International CISM-IFToMM Symposium, Moscow, USSR, April 1985, pp. 298-303. [8] Ballo, I. - Szuttor, N.; 1985: ACTIVE SYSTEMS IN VIBRATION CONTROL OF HEAVY MACHINE DRIVER'S SEATS. Noise Control Conference, Krakow, Poland Sept. 1985. Proceedings: pp. 43-50. [9] Stein, J.; 1985: AUTOMATED MEASUREMENT AND EVALUATION OF VIBRATION DAMPING PROPERTIES OF DRIVER'S SEAT. IMEKO 10th World Congress, Prague, CSSR, April 1985. Proceedings Vol. 9, pp. 102-109. [10] Stein, J. - Rujbrova, B.; 1985: AUTOMATED EVALUATION OF VIBRO-ISOLATING PROPERTIES OF OPERATOR'S SEATS. Noise Control Conference, Krakow, Poland Sept. 1985. Proceedings: pp. 779-784. [11] Stein, J. - Ballo, I.; 1986: AUTOMATED EVALUATION OF VIBRATION CONTROL PROPERTIES OF OPERATOR'S SEATS FOR EARTH MOVING VEHICLES ACCORDING TO THE ISO 7096-82 STANDARD (in Slovak). Strojnicky casopis Vol.37 (1986), No.5, pp. 557-568. [12] Stein, G. J. - Ballo, I.; 1991 : ACTIVE VIBRATION CONTROL SYSTEM FOR THE DRIVER'S SEAT FOR OFF-ROAD VEHICLES. Vehicle System Dynamics, Vol.20 (1991), No.1. pp. 57-78. [13] Margolis, D. L.; 1982: RESPONSE OF ACTIVE AND SEMI-ACTIVE SUSPENSIONS TO REALISTIC FEEDBACK SIGNALS Vehicle System Dynamics, Vol.11 (1982), No.3. pp. 267-282. [14] Griffin, M. J.; 1990 : HANDBOOK OF HUMAN VIBRATION. Academic Press, London 1990, pp. 405-408 [16] ISO 7096:82, Earth moving machinery - Operator seat - Transmitted vibration. First edition 1982-02-15. [17] ISO 2631/1:85, Evaluation of human exposure to whole body vibration - Part 1: General requirements. First edition 1985-05-15. ------------------------------------------------------------------------------- Stefan Markus, Assoc.Prof., M.Sc. (Eng), D.Sc. Phone: (+42 7) 254 751 INSTITUTE OF MATERIALS AND MACHINE MECHANICS Fax : (+42 7) 253 301 SLOVAK ACADEMY OF SCIENCES, Racianska 75, P.O.BOX 95 E-mail INTERNET: 830 08 Bratislava 38, Slovak Republic markus@umms.savba.sk ***************************************************************************** ITEM 3. AUSTRALIAN ACOUSTICAL SOCIETY. ***************************************************************************** The Society was incorporated as Company limited by guarantee in 1971 and it is governed by a Federal Council formed of representatives from each State in which there is a Division. Currently Divisions exist in N.S.W., Victoria, Western Australia, South Australia and Queensland. The Divisions are responsible for all local activities in their States, and from time to time they are invited to organise the Society's Annual Conference. There are nearly 500 members of the Society. The Society's main aim is to promote and advance the science and practice of acoustics in all its branches and to facilitate the exchange of information and ideas. In order to do this: An annual National Conference is organised by each State Division in turn. Here the latest research work, current developments and problems still to be solved in a variety of acoustics areas can be heard. The proceedings for these conferences are available for purchase from the Society. The 1995 Conference will be held near Perth in Western Australia from November 15 to 17 and the theme will be Acoustics Applied - putting the science and technology to work. Acoustics Australia, an internationally recognised, refereed journal is published by the Society. Australian and international papers on acoustics research and application are included, as well as information on coming acoustics events. It is distributed free to all members. For non members of the society it is available on subscription. Submissions of papers, notes, general news and advertising is welcomed. State Divisions organise regular meetings which can include talks, on-site visits, seminars and equipment demonstrations. These meetings allow members to meet people acquainted with the latest developments in their particular field, locally and internationally. From time to time the AAS organises a major international acoustics conference such as the lOth International Congress on Acoustics, Sydney, 1980, WESTPRAC IV, Brisbane, 1991 and INTER-NOISE 91, Sydney, 1991. The next ICBEN Conference will be held in Australia. The AAS liaises with national standards and policy setting bodies such as Standards Australia. Many of its members sit on committees involved with standards drafting and the development of state legislation. A high standard of research and application in acoustics is encouraged by the presentation of a President's prize at the Annual Conference and the National Excellence in Acoustics Awards. The Society has five grades of membership: honorary fellow, member, associate, subscriber, student and sustaining. This latter grade is for individuals or companies who actively support the Society. For information on the Society: General Secretary-AAS, Professional Centre, Private Bag 1, Darlinghurst, NSW 2010 Australia For information on the Journal Acoustics Australia: Acoustics Australia, PO Box 579 Cronulla NSW 2230 Australia or by email to the editors: m-burgess@adfa.oz.au Marion Burgess m-burgess@adfa.oz.au Tel : (06)268-8241 Fax : (06)268-8276 ***************************************************************************** ITEM 4. DEPARTMENT OF ACOUSTICS, MOSCOW STATE UNIVERSITY, RUSSIA. ***************************************************************************** This unique department was founded in 1943. It consists now of 50 Professors, Research workers and Engineers. Every year we have 15 - 20 graduate students and 3 - 5 post-graduates. Our students (Acousticians) are educated as specialists in Physics and Radiophysics. For the first 3 - 4 years they study general courses: General and Theoretical Physics, Mathematics, Theory of Vibrations, Wave Processes, Statistical Radiophysics, Solid State Electronics, Plasma Electronics, Computers in Radiophysics, etc. Special courses for our students are given in the 4-th and 5-th years. Some special programs are outlined below. Education is closely connected with research work. It is possible to divide all theoretical and experimental investigations carried out in recent years into four main areas: 1. Nonlinear Vibrations and Waves - Stochastic behaviour of dynamic systems - Self-excited Vibrations - Technical and Medical diagnostics - Nonlinear wave theory - Experiments on wave interactions in liquids and solids - Acoustic shock waves and damage of materials - Laser optoacoustics 2. Physical Acoustics of Solids - Nonlinear diagnostics,new nondestructive testing methods - Surface and wedge waves - Nonlinear elastic moduli measurement - Acoustics of high-temperature superconductors - Nonlinear magnetoacoustics - Acoustic microscopy 3. Underwater Acoustics - Diffractional tomography of inhomogeneities - Signal processing - Antenna synthesis - Noise measurements, models of underwater noise - Sound field at low frequencies - Vectoral-phase receivers 4. Aeroacoustics - Resonant-type absorbers for low-frequency and high intensive sound - Acoustic interferometers, intensimetry - Near fields and diagnostics of sound sources - Measurements in anechoic and reverberation chambers Our leading specialists and leaders of scientific groups: Dr. Sci. Vladimir A. Krasilnikov, professor Ph. D. Valentin A. Burov, professor Dr. Sci. Igor Yu. Solodov, professor Dr. Sci. Lev K. Zarembo, principal research scientist Dr. Sci. Polina S. Landa, principal research scientist Ph. D. Otar S. Tonakanov, associate professor Ph. D. Valerii A. Gordienko, senior research scientist Ph. D. Alexander I. Korobov, associate professor Ph. D. Pavel N. Kravtchun, associate professor Ph. D. Evgenii Ya. Tagunov, associate professor Ph. D. Oleg A. Sapozhnikov, associate professor Ph. D. Vera A. Khokhlova, research scientist Ph. D. Vladimir G. Mozhaev, research scientist Ph. D. Sergei N. Karpachev, research scientist Ph. D. Olga D. Rumyantseva, research scientist PROGRAMS OF COURSES 1995 1. Dynamics of continuous media for radiophysicists............ 2. Introduction to acoustics...................................... 3. Theoretical fundamentals of acoustics Part 1. Radiation and scattering of acoustic waves............. Part 2. Acoustic waves in bounded media........................ 4. Physical acoustics............................................. 5. Nonlinear acoustics............................................ 6. Acoustics of Ocean Part 1. Principles of underwater acoustics..................... Part 2. Statistical underwater acoustics....................... 7. Ultrasonic methods in solid state physics...................... 8. Noise and vibration............................................ 9. Inverse scattering problems in acoustics....................... 10. Nonlinear hydroacoustics....................................... 11. Sound absorbing systems........................................ 12. Acoustics of crystals and acoustoelectronics................... 13. Magnetoacoustics............................................... 14. Phenomena on the Ocean surface................................. 15. Foundations of vector-phase measurements of acoustic fields.... 16. Theory of vibrations and waves............................... Head of Department Professor OLEG V. RUDENKO Department of Acoustics Tel.: (095)939-2936 Faculty of Physics Fax : (095)932-5602 Moscow State University E-mail: Rudenko@na.phys.msu.su Moscow 11989, Russia ***************************************************************************** ITEM 5. FOURTH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION, ST. PETERSBURG, RUSSIA. ***************************************************************************** FOURTH INTERNATIONAL CONGRESS ON SOUND AND VIBRATION North Crown Hotel St. Petersburg, RUSSIA June 24-28, 1996 CONGRESS PROGRAMME The Congress programme will include keynote addresses and invited and contributed papers in specialized areas of sound and vibration. The Fourth Congress follows previous congresses held in the USA and Canada in 1990, 1992, and 1994. Several hundred people attended each previous congress. CONTRIBUTED PAPERS covering theoretical and experimental research in the following areas are solicited: 1. Aeroacoustics and Atmospheric Sound. 2. Boundary Element Methods. 3. Sound Intensity. 4. Diagnostics & Condition Monitoring. 5. Modal Analysis. 6. Material Characterization & Non-destructive Evaluation. 7. Statistical Energy Analysis. 8. Active Noise and Vibration Control. 9. Interaction of Fluid Motion and Sound. 10. Sound Radiation & Scattering. 11. Passive and Active Damping. 12. Finite Element Analysis. 13. Underwater Acoustics. 14. Architectural Acoustics. 15. Structural Acoustics and Vibration. 16. Human Response to Sound and Vibration. PUBLICATIONS Abstracts of contributed papers proposed for presentation at the Congress should be sent as soon as possible and must be received by the Congress Secretariat no later than December 31, 1995. Abstracts should be approximately 200 words in length. If the abstract is accepted, the paper must be typed on special manuscript sheets which will be supplied by the Congress Secretariat. The complete manuscript will be printed in the Congress Proceedings, and must be received no later than February 28, 1996. All written papers will be in English. The majority of lecture presentations will be in English. Keynote papers will have simultaneous translation into Russian and English, respectively. EXHIBITION Companies are invited to take part in the exhibition which will include instrumentation and electronics, acoustical apparatus and materials, sound and vibration isolation devices and software. Exhibition information and booth and table reservations are available from the Congress Secretariat. SOCIAL PROGRAMME St. Petersburg is one of the most beautiful cities in the world, The organizing committee will run special excursions, for the Conference participants, allowing them to see as many world-renowned masterpieces of Art and Architecture as possible. Participants may visit the Hermitage with its numerous art treasures, the many marvelous palaces, cathedrals and parks or go to the theatre, ballet, opera, or symphony concerts, etc. LODGING Participants will be accommodated in the North Crown Hotel. This is a new five star hotel with all modern conveniences. Single rooms are available starting from $105 per night (including breakfast). These rooms are available at the same rates for a limited time before and after the Congress dates. At your hotel you have an option to purchase two meals a day for the four-day period for an additional sum of $120. Airport transfers to and from the North Crown Hotel will be provided. This hotel is centrally located in the city near the River Neva. FURTHER INFORMATION The Congress registration fee is $310 US before December 31, 1995 and $330 US after that date. The registration fee includes the book of proceedings and cultural events including a visit to the Hermitage. Additional cultural events will be arranged before and after the Congress. Please make checks payable in US dollars drawn on a US bank for the registration fee payable to Sound and Vibration Congress and mail to the Congress Secretariat/USA. Those desiring to participate in the Congress should fill out the reply form and send it back to the organizing committee. REPLY FORM (Please return to the Congress Secretariat/USA) NAME__________________________________________________ POSITION______________________________________________ ADDRESS_______________________________________________ ______________________________________________________ ______________________________________________________ TELEPHONE_____________________________________________ FAX___________________________________________________ I plan to attend the Congress_________________________ I would like further information______________________ I intend to give a paper with the title of_____________ ______________________________________________________ ______________________________________________________ ______________________________________________________ I enclose an abstract_________________________________ (Abstracts due by December 31, 1995 at the latest) My company would like to exhibit a product at exhibition_________________________________________ _____________________________________________________ Papers accepted for the Congress will require a written version in Book of Proceedings. Written papers following the typing instructions and not exceeding 8 finished pages should be submitted by February 28, 1996 to the Congress Secretariat. All correspondence should be sent to the organizing committee: Conference Secretariat/USA and Overseas Countries Malcolm J. Crocker, Co-Chairman Fourth International Congress on Sound and Vibration Mechanical Engineering Department, 201 Ross Hall, Auburn University, Auburn, AL 36849-3501, USA Tel: (334) 844-3310 (Direct) or (334) 844-3248 (Direct) FAX: (334) 844-3306 E-mail: mcrocker@eng.auburn.edu Congress Secretariat/Russia Baltic State Technical University 1-st Krasnoarmeyskaya str., 1 St. Petersburg, RUSSIA 198005 Tel/FAX: (812) 316-15-59 ***************************************************************************** ITEM 6. INTER-NOISE 96, LIVERPOOL, ENGLAND. ***************************************************************************** UK Institute of Acoustics to organise 25th Inter-Noise Liverpool, England 30 July - 2 August 1996 The Silver Jubilee of the Inter-Noise conferences will be marked by an International Congress and Technical Exhibition, hosted by the UK Institute of Acoustics, from Tuesday 30 July through to Friday 2 August 1996. The congress is sponsored by the International Institute of Noise Control Engineering. The venue chosen is the recently refurbished Britannia Adelphi Hotel in Liverpool. The hotel dates from 1826 and is a reminder of the importance of Liverpool as the main european trading and emigration port on the Atlantic seaboard. It was reconstructed in 1912 to cater for transatlantic liner clients, and has historical connections with many famous visitors including Charles Dickens. The Edwardian elegance has been maintained and blended with all the features expected of a modern conference venue. Facilities include 3 restaurants, 4 bars, a health club with gym, sauna, solarium and swimming pool, a night-club and unrivalled conference and banqueting rooms. The General Chairman of the congress is Bernard Berry from the National Physical Laboratory in London, assisted by an organising committee representing the academic and commercial sides of the acoustics and noise control discipline in the UK. Nicole Porter of NPL chairs the Technical Programme Committee and, in keeping with the importance of the Silver Jubilee occasion, particular attention is being paid to the technical sessions. Work is already in hand to ensure that they contain unique and relevant material of interest to noise and vibration control professionals. An Announcement and Call for Papers will be issued in May 1995 and abstracts will be requested by December 1995. An International Advisory Committee of eminent noise control specialists is being assembled to ensure the quality and international relevance of the papers presented. The growing importance of international trading blocks, such as the European Union and the North American Free Trade Area, and the effect they are having on the harmonisation of legislation, will be a key strand running through the technical sessions. In what is essentially a regulations-driven industry, the effects of regulatory changes are having a profound technical impact, so, to ensure that legislators are fully briefed on the technical aspects of their free trade and fair competition programmes, invitations have been extended to key political figures. The city of Liverpool has a lot to offer the international visitor as a modern cultural centre which is steeped in the historical connections between the old and the new worlds. The congress hotel is located close to the historic waterfront where the River Mersey flows into the Irish Sea. Here the Albert Dock has now been completely redeveloped as a commercial and cultural centre and offers an interesting insight into the history of the area. With museums and many other attractions, delegates and accompanying persons will find an abundance to fascinate them. The social programme planned includes the opening reception to be held within the Merseyside Maritime Museum. This museum houses the "Emigrants to the New World" exhibition and vividly portrays the lot of those who left Europe to populate the Americas, contrasting what they left behind with what they found on arrival. The Conference Dinner will be held in the St George's Hall. This hall dates from 1842 and has been described as one of the most important public buildings of the past 200 years in the UK. The accompanying persons programme is planned to include the Beatles Magical Mystery Tour, River Mersey ferry cruises and organ visits to the Anglican and Roman Catholic Cathedrals. The Anglican Cathedral is a magnificent neo-gothic building and is the largest cathedral in the country, with the heaviest and highest ring of bells. It took 75 years to complete and is home to the largest church organ in the country. Nearby, too, is the city of Chester, famed for its unique medieval buildings and the complete city wall, with evidence of every period of history since Roman times. Communications with the city of Liverpool are excellent. There is a regional airport with regular connections to London, and Manchester International Airport is only one hour away by direct rail link. The Britannia Adelphi Hotel adjoins the main rail station, which is part of the inter-city network connecting with all parts of the UK, and Northern Europe via the Channel Tunnel. Motorway links to the city are also plentiful, allowing those who wish to stay in the countryside to have easy access to the congress venue. Those wishing to extend their stay will find that they are conveniently located to explore the dramatic scenery of North Wales, the English Lake District, the Peak District and Scotland. Alternatively, crossing the Irish Sea offers the chance to explore at first hand the origins of Liverpool's (and America's) Irish community. To the east, past the mills that turned American cotton into fine linen, there is the peaceful beauty of the Yorkshire Dales. To the south the visitor can find tangible evidence of the industrial archaeology of the UK at such places as Ironbridge Gorge, which is credited with being the cradle of the Industrial Revolution. Indeed a veritable treasure trove awaits those from overseas whose experience so far has been limited to the geography and peoples of London and the south-east areas of England. Further information on the Congress, the Exhibition and the associated activities can be obtained from the Institute of Acoustics, Agriculture House, 5 Holywell Hill, St Albans, Hertfordshire, AL1 1EU (UK Facsimile +44 (0)1727 850553). Charles Gregory ralph@rafihmt.org.uk ***************************************************************************** ITEM 7. 2nd INTERNATIONAL CONFERENCE ON ACOUSTIC AND MUSICAL RESEARCH. ***************************************************************************** CIARM 95 2nd International Conference on Acoustics and Musical Research Ferrara, Italy, 19-21 May, 1995 The Conference is scheduled from May 19 to 21, 1995 and will be held at the Ferrara Fair area (Quartiere Fiera di Ferrara), Via Bologna 534. The official opening will take place in the morning of May 19 and the registration desk will be open, on the same day, from 10.00 am to 6.00 pm. Participants are requested to pick up registration materials at this time, if possible. The registration desk will also be open from 9.00 am to 6.00 pm on Saturday, May 20 and from 9.00 am to 4 pm on Sunday, May 21. Coming to Ferrara Ferrara is located 40 km away from Bologna and is conveniently rail-linked to it. Bologna has excellent railway connections from/to Paris, Munich, Vienna and daily airline connections from/to Bruxells, Frankfurt, London, Paris and Vienna, Weekly airline connections are also available from other countries. By road, Ferrara can be reached through the A13 Bologna - Venice motorway. Accommodation For accommodation, please call directly the hotels in Ferrara or Bologna and mention the CIARM 95 Conference. It is important to make a reservation as soon as possible because the number of rooms within each category is limited and rooms will be allotted on the basis of availability. The list of the hotels can be obtained from the Conference Secretariat. Registration Fee The registration fee, for each participant, is Lit. 130.000 if paid before March 31, 1995 or Lit. 160.000 after this date. The registration fee includes the Conference documents and proceedings and the admission to all the sessions and technical exhibits. The payment must be made by check, made payable to Pangea Service, or by bank transfer sent to the following account: COMIT, C.so Porta Reno-44100 FERRARA-ITALY c/c N. 6585921 02 46 entitled to PANGEA SERVICE Bank transfers must be totally free of expense for the receiver. Social Event During the Conference period, at the Municipal Theater of Ferrara, Rotonda Foschini, 4, Mozart's "Magic Flute", conducted by J.E. Gardiner, will be performed. Participants intersted in attending this event, should book tickets directly at the ticket office of the theater, Corso Giovecca, 10/12, tel.: +39/532/202675, FAX: +39/532/249391. For more information contact the Conference Secretariat at: CIARM 95 Secretariat National Research Council of Italy Cemoter Acoustics Department Via Canal Bianco, 28 I-44044 Cassana, Ferrara, Italy tel: +39 532 731571 FAX: + 39 532 732250 E-mail: CIARM95@cnrfe1.fe.cnr.it ***************************************************************************** ITEM 8. THE FOURTH SESSION AND ADVANCED STUDY SCHOOL ON "ACOUSTICAL MEASUREMENTS, METHODS AND INSTRUMENTS". ***************************************************************************** RUSSIAN ACOUSTICAL SOCIETY (RAS) N.N. ANDREYEV ACOUSTICS INSTITUTE have the honour to invite you to the Fourth Session and Advanced Study School ACOUSTICAL MEASUREMENTS METHODS AND INSTRUMENTS The Fourth Session and Advanced Study School of the Russian Acoustical Society on "Acoustical Measurements. Methods and Instruments" will be held in Moscow, Russia, May 23-25, 1995. SCOPE - Measurements of the Basic Parameters of Acoustic Fields in Natural Media. (Ocean, Earth-Crust, and Atmosphere). - Control of Acoustical Characteristics in Architectural, Building, and Musical Acoustics and in Industrial Technologies. - Measurements of the Characteristics of Electroacoustic Transducers and Arrays. - Acoustical Measurements in the Field of Control and Suppression of Noise and Vibration. - The Problems of Standardization and Reference Standards. THE PROGRAM INCLUDES: - Plenary papers - Invited papers - Poster session - Technical exibition ORGANIZING COMMITTEE DUBROVSKY NIKOLAI A. - chairman, President of the Russian Acoustical Society tel.(095)126-7401 YUDINA ELENA B. - co-chairman, executive director of the Russian Acoustical Society tel.(095)126-9835 KAZANTSEV VSEVOLOD F. - member CHERNYSHOV VADIM B. - member LOPASHOV DMITRII Z. - member PROGRAM COMMITTEE FURDUEV ALEKSANDR V. tel.(095) 126-9865 GOLYAMINA IRINA P. (095) 126-9892 TROKHAN ALEKSANDR M. (095) 535-0830 VINOGRADOVA ELEONORA L. (095) 158-2923 SECRETARIAT MAZENKOVA IRINA V. (095) 126-9927 ADMINISTRATIVE GROUP UL'YANOV VLADIMIR N. (095) 126-9043 REGISTRATION The payment for foreign participants will be 200 US dollars and 100 US dollars for accompanying persons. The cost of participation at the exibition will be announced later. The payment should be made before May 1, 1995 and the money should be addressed in the name of the Russian Acoustical Society to the International Moscow Bank for the transit account N 40023 USD 4005 02, or to the Bank of New York for the transit account N 8900060611, or to the Barclays Bank for the transit account N 52053722 (current account N 070021006 of the Commercial Bank "Most-Bank"). CONTRIBUTED PAPERS The English and the Russian languages are the official languages of the Session. Proceedings of the Session and Advanced Study School are planned to be printed in Russian and in English. Sponsors of the Session and Advanced Study School are welcome to make a report and have a publication in the Proceedings. The Participants will be provided with the Proceedings at the expense of the Organizing Committee. Other persons or organizations interested may order Proceedings before May 15, 1995 by paying in advance $50 and $45 (postage). ACCOMMODATION - will be arranged for participants on request. TRANSPORTATION - between the airport, hotels and the Acoustics Institute will be provided at the expense of the Organizing Committee. SOCIAL PROGRAM - will be arranged on request (including local tours around Moscow). THE ORGANIZING COMMITTEE would very much appreciate it if you would pass on information about our Session to your colleagues! CORRESPONDENCE Mailing address: N.N.Andreyev Acoustics Institute Russian Acoustical Society 4, Shvernik st., Moscow, 117036 RUSSIA Telephone: +7 (095) 126-7401 +7 (095) 126-9835 FAX: +7 (095) 126-8411 E-mail: bvp@asu.acoins.msk.su PARTICIPATION FORM IV SESSION AND ADVANCED STUDY SCHOOL "ACOUSTICAL MEASUREMENTS METHODS AND INSTRUMENTS" NAME________________________________ ____________________________________ FIRST NAME__________________________ ORGANIZATION________________________ ____________________________________ MAILING ADDRESS_____________________ ____________________________________ TELEPHONE___________________________ FAX_________________________________ E-MAIL______________________________ TITLE OF PRESENTATION_______________ ____________________________________ ____________________________________ EXIBITION___________________________ DEAR COLLEAGUE, Please fill in this form and mail or fax it as soon as possible. ***************************************************************************** ITEM 9. WAYNE TUSTIN AGAIN TEACHING VIBRATION ***************************************************************************** WAYNE TUSTIN AGAIN TEACHING VIBRATION Wayne Tustin is once again available to teach engineers and technicians about the basics of vibration and shock testing, measurement, analysis and calibration, also about ESS (environmental stress screening.) Tutorial attendees at the Institute of Environmental Sciences annual technical meeting, Anaheim, California May 1-4 and at the SAE noise and vibration conference, Traverse City, Michigan May 15-18 will be his first audiences. Wayne Tustin and fellow reliability specialists can be reached through the Equipment Reliability Group at 2512 East. Main St., Mesa, Arizona 85213, telephone 602/649-4077. Wayne Tustin's e-mail address is 71460.3041@compuserve.com. Alternately, option 2# on SkyTel pager 1-800-217-6828 accepts voice messages. Vibration and shock environmental tests are conducted in the development labs of numerous organizations. Production areas use random vibration as an ESS (environmental stress screening) tool. Over the past few years, many organizations have lost their experienced vibration and shock experts through attrition, reductions in force, layoffs, mergers and acquisitions. Thus some of today's employees are not familiar with the practical aspects of vibration and shock testing and screening, and these courses are designed for them. Wayne Tustin 71460.3041@compuserve.com ***************************************************************************** ITEM 10. ARCHITECTURAL ACOUSTICS SIMULATION. ***************************************************************************** I hope that you can provide me with some information on the following topic. We are developing architectural simulations and wish to add realistic sound effects. Specifically, we would like to be able to model the frequency response of a room. That is, if a sound source is placed at position x and a receiver at position y, what are the characteristics of the signal that reaches y? Not knowing anything about acoustical modelling, I am using an approach derived by analogy from geometrical optics. I have three questions: a) Is a ray tracing approach appropriate? b) What work has already been done along these lines? Is there software (commercial or public domain) for performing this kind of computation? c) Can you provide me with pointers to modern references on acoustical simulation? Thank you in advance for any help that you may be able to give me. Murray Heggie (mheggie@vrlab.uccb.ns.ca) _______ NOTE: READERS SHOULD REPLY DIRECTLY TO MR. HEGGIE. (Thank you, The Editors) ***************************************************************************** ITEM 11. "ENGINEERING VIBRATION" BY DANIEL J. INMAN. ***************************************************************************** Engineering Vibration, by Daniel J. Inman Prentice Hall, 1994, 9 by 6.5 inches, 560 pages Dr. Inman's textbook offers a number of new ideas in the presentation of traditional undergraduate vibrations. In addition to many exercise problems, each chapter includes computer exercises to be carried out using the MATLAB Vibrations Toolbox (included with the book). The book is also particularly effective at jumping in and getting the student solving real engineering vibrations problems. Laplace Transforms and the Convolution Integral are introduced very early on, and revisited throughout the text. However, these topics may be delayed or skipped entirely because the traditional methods of solving differential equations with trial functions are also covered. At the same time, the book completely covers the fundamentals of undergraduate vibrations in five chapters. The author saves space by focusing on the key results from the different classical problems. The remainder of the book deals with more advanced topics such as continuous systems, finite elements, and nonlinear vibrations. The book presents the analyses of different classes of problems and summarizes the steps and results in highlighted tables. For example, the book includes a table of natural frequencies and mode shapes for a variety of slender beam boundary conditions (similar to Blevins' Formulas for Natural Frequency and Mode Shape). This enhances the book's value as a reference text. In short, Dr. Inman's Engineering Vibration is a well written and clear guide to undergraduate vibrations. The book offers fresh coverage of classic topics in an easily understood style. Table of Contents: 1. Introduction to Vibration and the Free Response 2. Response to Harmonic Excitation 3. General Forced Response 4. Multiple Degree of Freedom Systems 5. Design for Vibration Suppression 6. Distributed-Parameter Systems 7. Vibration Testing and Experimental Modal Analysis 8. Finite Element Method 9. Computational Considerations 10. Nonlinear Vibration ---------- Eric Marsh Assistant Professor Penn State University 322 Reber Building University Park, PA 16802 (814) 865-5242 phone (814) 863-8682 fax E-mail: erm7@psu.edu ***************************************************************************** ITEM 11. 3-D SOUND FOR VIRTUAL REALITY AND MULTIMEDIA. ***************************************************************************** Title: 3-D sound for Virtual Reality and Multimedia Author: Durand R. Begault Ph.D., NASA Ames Research Center Publisher : Academic Press Professional c. 290 pages 6x9 hardbound $49.95 ISBN: 0-12-084735-3 Ordering: 1-800-3131-APP; international 1-4017-345-2525; email orders app@acad.com; at many technical bookstores. WWW URL (picture of the cover and brief description): http://bookweb.cwis.uci.edu:8042/Books/Academic/Indiv/Begault-3DSound.html Overview: The first comprehensive book on 3-D sound for VR and multimedia applications. key features include: introductions to physics and perception of sound and DSP related to spatial hearing; covers the implementation of a 3-D sound system for control of azimtuh, elevation and distance of virtual sound sources; includes discussion of reverberation modeling and auralization for acoustical desgin; overviews many differnet applications for spatialized sound, including: auditory feedback; communication systems; aeronautics; computer music; sonification; television; and computer interfaces. Detailed TOC: -Chapter One. Virtual Auditory Space: Context, Acoustics, and Psychoacoustics Context Source-Medium-Receiver Model: Natural versus Virtual Spatial Hearing Application Types Virtual Audio: A Special Case Components So What Is 3-D Sound Good For? Surround versus 3-D Sound Characteristics of Sound Sources Describing Waveforms Periodic and Aperiodic Waveforms Digital Sound and Signal Processing Harmonics Fourier Analysis Amplitude Envelope Perception Psychoacoustics and Applications Perceptual Correlates of Frequency, Intensity, and Spectral Content Cognition -Chapter Two. Overview of Spatial Hearing Part I: Azimuth and Elevation Perception Interaural Time and Intensity Cues Lateralization Physical Basis of Lateralization ITD Envelope Cue Perception of Lateralization The Precedence Effect ITD, IID, and Barn Owls: A Neurological Processing Model Head Movement and Source Movement Cues Head Movement Moving Sound Sources Spectral Cues Provided by the Pinnae Ambiguous ITD and IID Cues The Head-Related Transfer Function A Do-It-Yourself Experiment with Spectral Modification HRTF Magnitude Characteristics HRTF Phase Characteristics Localization with HRTF Cues Spectral Cues Provided by the HRTF Spectral Band Sensitivity Localization of Actual Sound Sources with HRTF Cues Localization of Azimuth and Elevation of Virtual Sources Nonindividualized HRTFs Reversals -Chapter Three. Overview of Spatial Hearing Part II: Sound Source Distance and Environmental Context 3-D Sound, Distance, and Reverberation Distance Cues Intensity, Loudness Cues Influence of Expectation and Familiarity Spectral and Binaural Cues to Distance Spectral Changes and Sound Source Distance Frequency Dependent Attenuation at Large Distances Binaural Cues and Intensity Inside-the-Head Localization: Headphone Distance Error Reverberation Physical Aspects of Reverberation Perceptual Aspects of Reverberation Late Reverberation The R/D ratio and Distance Perception The Auditory Horizon Effect of Reverberation on Azimuth and Elevation Estimates Specific Perceptual Effects of Early Reflections Echolocation Timing and Intensity Concert Hall Reverberation -Chapter Four. Implementing 3-D Sound: Systems, Sources and Signal Processing Considerations for System Implementation Audio System Taxonomy Hardware and Software Integration Requirements Distributed versus Integrated Systems Perceptual Requirements DSPs for 3-D Sound Simulation Overview Thumbnail Sketch of DSP Theory Impulse Response of a System Simple DSP Systems Implementation of Lateralized Positions Digital Filtering and Convolution Implementing HRTF Cues Measurement of Binaural Impulse Responses Using Digital Filters for HRTFs Collecting HRTF Measurements Calculation of Generalized HRTF Sets Equalization of HRTFs Data Reduction of HRTFs Methods for Data Reduction Example Procedure for Formulating Synthetic HRTFs Interpolation, Moving Sources, and Head Movement Implementation Problems with Interpolation Algorithms Implementing Distance and Reverberation Models Distance Simulation Environmental Context Simulation Convolution with Measured Room Impulse Responses Synthetic Reverberation Auralization: HRTFs and Early Reflections Overview of Auralization Theory Implementation Summary -Chapter Five. Virtual Acoustic Applications Introduction Speech and Nonspeech Audio Input Representational Sounds An Aeronautical Application of Auditory Icons A Case Example: Illustrating MIDI Communication Head-Tracked 3-D Audio for Virtual Environments Crystal River Engineering Focal Point A Virtual Reality Application: NASA's VIEW System Computer Workstation 3-D Audio A Generic Example Audio Windows Audio GUIs for the Blind Recording, Broadcasting , and Entertainment Applications Loudspeakers and Cross-talk Cancellation Binaural Processors for the Recording Studio AKG Corporation's Binaural Consoles HEAD acoustics Roland Corporation HRTF-Pseudo-Stereophony Voice Communication Systems Binaural Advantages for Speech Intelligibility The Ames Spatial Auditory Display Aeronautical Applications Head-up Spatial Auditory Displays Auralization Applications The Music of the Future is the Music of the Past 3-D Techniques Applied to Headphone Music Gordon Mumma: Audioearotica -Chapter Six. Resources. Finding Pertinent Information Books and Review Articles Virtual Reality Inspirational and Informative Works Light Technical Overviews Heavy-weight Technical Overviews Multimedia Sound and Psychoacoustics Digital Audio and Computer Music Sound System Design Spatial Hearing References Room Acoustics and Perception Anthologies and Proceedings Journals HRTF Measurements 3-D Sound Systems and Audio Cards 3-D Audio Systems Sound Systems (Synthesis, Analysis, and Hardware) Head Trackers and Other Interactive Sensors Auralization Tools Headphones and Dummy Heads Relevant Software 3-D Recordings Patents -References -Index Durand Begault Ph.D. MS 262-2 Room 130 NASA Ames Research Center Moffett Field CA 94035-1000 415 604 3920 FAX 415 604 3323 ***************************************************************************** ITEM 13. ACTIVE NOISE CONTROL AND GROUP DELAY. ***************************************************************************** When implementing an active noise control system in a duct, for example, to control band limited random noise, the minimum allowed distance between the reference sensor and control source is dependent of the group delay through the electronic controller. The group delay through the controller includes the delay through any high or low pass filters in the reference signal path as well as the delay from the input to the output of the loudspeaker control source. The total system delay must be less than the delay in the acoustic path in the duct between the reference sensor and the control source. In a recent installation to control a band limited noise centred on 31.5 Hz in an air conditioning duct (as a result of flow instability caused by fan inlet dampers) it was found that the group delay from the electrical input to the control source to the acoustical output from it was 8m seconds at 31 Hz and 5m seconds at 63 Hz. This delay coupled with delays through antialiassing filters as well as a high pass filter to remove unwanted 19 Hz flow noise from the reference sensor signal, resulted in a total system delay of 15m seconds at 31 Hz which meant that the reference sensor and control source had to be a minimum of 5.5 m apart for good performance to be achieved. Removal of the 19 Hz noise from the reference signal was necessary because it dominated the spectrum in the duct by about 10 dB but was not a problem in the office spaces serviced by the duct. When the 19 Hz noise was present in the reference signal, the controller attempted to drive the loudspeaker to reduce its presence in the error signal. The loudspeaker was incapable of sufficient output for control at this frequency with the result that the controller became unstable. The delay through the control source was a function of the loudspeaker and the characteristics of the acoustic enclosure for the loudspeaker which was specially designed to produce a maximum output in the 31.5 Hz octave band. It is clear that for this low frequency problem, the most significant causes of the group delay were not associated with the signal processing electronics but with the filters and the control source. These latter delays are unavoidable and determined by the physics of the problem - faster processors do not help. Fortunately these same delays reduce drastically as the frequency of the sound to be controlled increases, thus allowing the control source to be placed much closer to the reference sensor. Also at very low frequencies, it is questionable whether the system needs to be entirely causal and slightly higher delays through the electronic controller than through the acoustic path in the duct may be tolerable. An important practical item of information is that the front and rear sides of the loudspeaker should be connected by a small airway. Otherwise the speaker cone will be forced to one end of its travel by the pressure in the duct, severely degrading its performance and most likely leading to it being damaged when active control is attempted. Regarding the turbulence filters for microphones, we found that for a flow speed of 23m/sec, a 2m length of 11.5 mm OD x 2mm WT, Vyon-F porous tube from Porvair (Fax +44 553 764637) placed inside another Vyon-F tube, 22 mm OD x 3.2 mm WT was very effective. Dr. Colin Hansen CHANSEN@edison.aelmg.adelaide.edu.au ***************************************************************************** End of the fourth issue of the ISV Digest