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NAVAL POSTGRADUATE SCHOOL Monterey California , THESIS mm A< OUS'l IC IMPI-DANCli OF MA ITR1AFS FROM RFVFRHFRATION IMF I In Antonio Carocbo .1. December 1991 < 'o-Advisor Alan Cop-pens II. Co-Advisor James V. Sanders Approved for public release; distribution is unlimited. 2^7753 T reclassified airily classification of this pag RFPORI DOC IM1.M A ION PACK I a Report Security Classification I reclassified lb Restrictive Markings •i Secuntv Classification Authority .3 Distribution Availability ol k , rl n Declassification Down^radm;; Schedule Approved for public release; distribution is unlimitt Performing Organization Report Numbers') Monitoring Oiganization Report Number 1 Name ofPerforming Organization 6b Office Symbol 7a Name of Monitoring Organization [aval Postgraduate School (ifapplicabln) 33 Naval Postgraduate School : Address (city, stale, and ZIP code) 7b Address (dry, state, and ZIPcode) lonterev, CA 93943-5000 Monterey, CA 93943-5000 i Name of Funding Sponsoring Organization 8b Office Symbol 9 Procuiement Instrument Identification Number (ifapplicable) Address (ciry, state, andZIP code) 10 Source of funding Numbers Program Element No Proiect No Task No Work Lnit Accession No Title (includesecurity classification) ACOUSTIC IMPEDANCE OF MATERIALS FROM REVERBERATION TIME (Un- assified i l Personal Author(s) Antonio .!. Carocho JaType of Report 1.3b Inne Covered 14 Date of Report Iyear, month, day) 5 Pasgee2?un Raster's Thesis Prom 1o December 1991 ; Supplementary Notation The views expressed in this thesis are those of the author and do not reflect the official policy or po- tion of the Department of Defense or the U.S. Government. 1 Cosati c IS Subject Terms (continue on reverie if necessary andidentify by block nunibi ield Subgroup Reverberation , Impedance, Acoustics ) Abstract (continue on reverse ifnecessary andidentify by block number) A theoretical model is derived to calculate the specific acoustic npedance of the absorptive materia! covering the walls of a cavity. This model will allow the experimental determination fthe specific acoustic impedance from the measurement ofthe reverberation time hi a water-filled cavity. '1 he model assumes wall ol low absorption. It can not be used lor rigid or pressure release walls and grazzing incidence is excluded. 3 Distribution Availability ofAbstract 21 Abstract Security Classification D 3 unclassified unlimited same as report DT1C users Unclassified 2a Name of Responsible Individual 22b Telephone (includeArea code) 22c Office Symbol dan B. Coppens (408) 646-2847 D TORM 1473.S-; MAR S3 APR edition may be used until exhausted security classification of this page All other editions are obsolete Unclassified Approved for public release; distribution is unlimited. Acoustic Impedance of Materials from Reverberation lime by Antonio J. Carocho Lieutenant Portuguese Navy , B.S., Portuguese Naval Academy, 1982 Submitted in partial fulfillment ofthe requirements for the degree of MASTER OF SCIENCE IN ENGINEERING ACOUSTICS from the NAVAL POSTGRADUATE SCHOOL December 1991 7" \f Anthony y^tchley, Chairman, Engineering Acowstics Academic Commitee ABSTRACT A theoretical model is derived to calculate the specific acoustic impedance of the absorptive material covering the walls of a cavity. This model will allow the experimental determination of the specific acoustic impedance from the measurement of the reverberation time in a water-filled cavity. The model assumes a wall of low absorption. It can not be used for rigid or pressure release walls and grazzing incidence is excluded. iii TABLE OF CONTENTS INTRODUCTION MOTIVATION A. OBJECTIVE B. . . METHOD C. . . . REMARKS D. . . LITERATURE REVIEW II. 2 A. CHAMBER EOR REVERBERANT ACOUSTIC POWER MEASURE- MENTS IN AIR AND WATER [REF. 1] 2 B. REVERBERATION TIME, ABSORPTION, AND IMPEDANCE [REF.2J 2 . C. SABINE REVERBERATION EQUATION AND SOUND POWER CAL- CULATIONS [REF.3] 3 D. REVERBERATION TIME IN ENCLOSURES [REF.4] 4 OTHER LITERATURE E. 4 THEORETICAL MODEL III. 6 A. REVERBERATION IN CAVITIES 6 DAMPED NORMAL MODES B. 7 APPLICATION C. 9 SOLUTION 1. (general) II RESULTS 2. 14 CHECKS 3. 16 a. Main assumption 16 b. Normal incidence 16 c. Power reflection coefficient 17 CONCLUSIONS IV. 18 LIST OF REFERENCES 20 INITIAL DISTRIBUTION LIST 21 iv