| Bone Conducted Noise and Mitigation Techniques |
Mar-2009 |
20 pages |
| Authors:
Richard L McKinley; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH HUMAN EFFECTIVENESS DIRECTORATE
|
 | Very high level noises, up to 150 dB, can cause special problems in hearing protection. In order to achieve a 15 minute exposure within an 85 dB, 8 hour, 3 dB/doubling criteria, the hearing protector must provide 50 dB of overall noise attenuation. The issue becomes the flanking pathway provided by bone conduction with an attenuation at 2 kHz of approximately 40-45 dB. In this case, the flanking pathway becomes ... |
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| Sound Attenuation from Earmuffs and Earplugs in Combination: Maximum Benefits vs. Missed Information |
Sep-2006 |
|
| Authors:
Patricia Odell; Sharon M Abel; DEFENCE RESEARCH AND DEVELOPMENT TORONTO (ONTARIO) JUDGEMENT AND DECISION-MAKING GROUP
|
 | High noise levels from aircraft, small and large caliber weapons, land vehicles, ships, or submarines are characteristic of military operational environments. Continuous levels in the interior of fixed or rotary wing aircraft or in the vicinity of jet engines range from 100 - 130 dBA (15,18). Peak sound pressure levels from impulse noise produced by a howitzer may be as high as 180 dB SPL (28). Small caliber weapons such ... |
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| Sound Attenuation of Rotary-Wing Aviation Helmets with Oregon Aero(Trademark) Earcup Replacement Products |
OCT 2005 |
61 pages |
| Authors:
Elmaree Gordon; William A. Ahroon; Melinda E. Hill; ARMY AEROMEDICAL RESEARCH LAB FORT RUCKER AL
|
| The sound attenuation of the HGU-56/P Aircrew Integrated Helmet System (AIHS) and the HGU-84/P Rotary-Wing Helmet System (RWHS) configured with Oregon Aero(Trademark) replacement earcup products was evaluated in accordance with the American National Standard Methods for Measuring the Real-Ear Attenuation of Hearing Protectors [ANSI S12.6-1997 (R2002)], Method A: Experimenter-supervised fit. Sound attenuation of both the HGU-56/P AIHS and HGU-84/P RWHS configured with the Oregon Aero HushKit(Trademark) replacement earcup foam or ... |
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| Spatial and Temporal Variations in Sediment Compressional Wave Speed and Attenuation Measured at 400 KHZ for SAX04 |
SEP 2005 |
10 pages |
| Authors:
Kevin B. Briggs; Michael Zimmer; Michael D. Richardson; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS SEAFLOOR SCIENCES DIRECTORATE
|
| Diver cores were collected from various locations within the SAX04 site from 21 September to 3 November 2004 and compressional wave speed and attenuation were measured every centimeter at 400 kHz. Although measured values of sound speed and attenuation fall within established ranges for archived data from similar medium quartz sands, fluctuations in measured values were observed in the data that can be explained by the pattern of storm events ... |
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| Frequency Dependent Sound Speed and Attenuation Measurements in Seafloor Sands from 1 to 400 KHZ |
SEP 2005 |
9 pages |
| Authors:
M. A. Zimmer; L. D. Bibee; M. D. Richardson; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
|
| As part of the SAX04 experiment, sound speed and attenuation were measured in the seabed off of Ft. Walton Beach, Florida, USA, at frequencies from 1 to 400 kHz. For the lowest frequencies, from 1 to 20 kHz, signals from two acoustic sources were recorded on an array of hydrophones emplaced at depths of up to 1 m below the seafloor within a 4 m by 4 m area. At ... |
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| Morphology of Gas Bubbles in Mud: A Microcomputed Tomographic Evaluation |
JUL 2005 |
9 pages |
| Authors:
Allen H. Reed; Bernard P. Boudreau; Chris Algar; Yoko Furukawa; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS SEAFLOOR SCIENCES DIRECTORATE
|
| Free gas in surficial sediments commonly forms gas bubbles that attenuate and dampen acoustic waves, influence slope stability, and contribute to greenhouse gas concentrations. Therefore, determining the mechanisms that control bubble shape, size, growth, and migration is important to acoustic sediment characterization and other disciplines. Previously, gas bubble shape, size, and distribution was quantified using "low-resolution" (~500 micron) medical computed tomography (CT). Recently, "high-resolution" (to 30 microns. In several MR ... |
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| Double protection passive pour les equipages de l'helicoptere d'attaque "Tigre" : Concept et etude experimentale (Design and Experimental Study of the Passive Double Hearing Protection for the Crew of the Attack Helicopter "Tiger") |
01 APR 2005 |
15 pages |
| Authors:
J. Baudou; G. Reynaud; G. Poussin; A. Leger; THALES AVIONICS LE HAILLAN (FRANCE)
|
| Les coques des ecouteurs du casque Topowl ont deja fait l'objet d'une etude visant a optimiser leur protection auditive dans les stricts budgets de masse et de volume impartis. La presente demarche consistait donc a selectionner puis evaluer des solutions permettant d'ameliorer sensiblement cette protection face aux niveaux de bruit plus eleves que prevu releves en cockpit. Par sa simplicite de mise en oeuvre, sans impact sur le casque, son ... |
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| Investigating Double Hearing Protection using Human Subjects |
APR 2005 |
|
| Authors:
Christopher Tubb; Susan Mercy; Soo James; QINETIQ FARNBOROUGH (UNITED KINGDOM) HUMAN FACTORS IN ACOUSTICS AND VIBRATION
|
| With the growing need to protect the hearing of military personnel, the use of double protection, earplugs and earmuffs used in combination, has become more and more prevalent. Furthermore Active Noise Reduction (ANR) headsets and earplugs appear to offer a means of increasing the attenuation of these double protection systems. However, it has been shown that the attenuation afforded by double protection is not a simple additive process; the combined ... |
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| Sound Speed and Attenuation Measurements in Unconsolidated Glass Bead Sediments Saturated With Viscous Pore Fluids |
28 JUN 2004 |
29 pages |
| Authors:
Brian T. Hefner; Kevin L. Williams; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| During the sediment acoustics experiment (SAX99) independent sound speed and attenuation measurements were made in a well-characterized sandy sediment. These measurements covered a broad frequency range that made it possible to test both Biot theory and Buckingham's more recent grain-to-grain attenuation model. Biot theory was able to model sound speed well but was unable to predict attenuation measured above 50 kHz. A series of measurements was made in the laboratory ... |
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| Insertion Loss of the HGU-84/P Rotary-Wing Helmet System with Oregon Aero Earcup Replacement Products |
FEB 2004 |
279 pages |
| Authors:
William A. Ahroon; Melinda E. Hill; Elmaree Gordon; Martin B. Robinette; ARMY AEROMEDICAL RESEARCH LAB FORT RUCKER AL
|
| The sound attenuation of the H6U-84/P Rotary-Wing Helmet System with Oregon Aero earcup replacement products was evaluated in accordance with ANSI s12.42-1995 (R1999) Microphone-in-Real-Ear procedures. The differences in insertion losses between the various helmet modifications were generally quite small and unlikely to have an effect on operational considerations, especially if double hearing protection in the form of earplugs, the Communications Earplug (CEP), or Attenuating Custom Communications Earphone System for Aircrew ... |
|
| iMAST Quarterly, Number 1, 2004 |
Jan-2004 |
9 pages |
| Authors:
APPLIED RESEARCH LABORATORY STATE COLLEGE PA
|
| This quarterly briefly addresses engine fretting evaluation. The feature article is titled Light Armored Vehicle Noise Control. Exploiting the acoustics expertise resident at ARL Penn State, engineers were asked by the Marine Corps to address noise issues related to the Light Armored Vehicle. The integration of advanced materials, manufacturing processes, health monitoring, and acoustic tailoring promotes reductions in gross weight, vibration, interior noise, and life-cycle cost, as well as increases ... |
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| The Effects of Physical Composite Particle Parameters on The Efficacy of a Proprietary Sound-Attenuation Technology and it's Application to Advanced Structural Composites |
28 MAR 2003 |
6 pages |
| Authors:
Chuck Zhang; FLORIDA AGRICULTURAL AND MECHANICAL UNIV TALLAHASSEE COLLEGE OF ENGINEERING
|
| Two principal objectives were proposed in this research: (1) determine the acoustical effects of the filler materials with different sound impedance in composites fabricated according to a proprietary technology, and (2) determine the feasibility of applying the proprietary technology to continuous fiber-reinforced advanced structural composites. The sequential experimental approach began by attempting to apply the acoustical technology with neat epoxies using off-the-shelf filler materials possessing a range of physical characteristics. ... |
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| A Nondimensional Parameterization for Sound Propagation in the Atmosphere |
MAR 2003 |
22 pages |
| Authors:
Michael Mungiole; D. K. Wilson; ARMY RESEARCH LAB ADELPHI MD
|
| Parabolic equation (PE) techniques have been successfully used to obtain numerical solutions of sound pressure attenuation in which sound propagation is affected by turbulence and vertical gradients in wind and temperature. The PP models generally produce accurate attenuation values, but the execution time is excessive for applications when near real-time results are required. To obtain sound level attenuation predictions at selected location more quickly, we are developing an artificial neural ... |
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| Jet Engine Test Cell Noise Reduction |
AUG 2000 |
77 pages |
| Authors:
C. A. Kodres; NAVAL FACILITIES ENGINEERING SERVICE CENTER PORT HUENEME CA
|
| Passive methods for decreasing jet engine test cell noise emissions are evaluated and compared. Such methods have the dual advantages of low cost and simplicity. In addition, the effect on the aerothermal performance of the test cell is minimal. Sound pressure levels were measured in and around test facilities equipped with various devices to further reduce noise. The data were supplemented with parametric studies of ... |
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| Mass Loaded Coating and Method for Reducing the Resonant Frequency of a Ceramic Disc |
26 OCT 1999 |
|
| Authors:
Patrick J. Monahan; DEPARTMENT OF THE NAVY WASHINGTON DC
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| A mass-loaded coating includes a predetermined mass of powdered lead which is mixed preferably in a ratio of 3:1 with a liquid polyurethane primer. When painted onto the surface of a disc or plate, the coating mass-loads the disc and lowers the resonant frequency of the disc without significantly increasing the physical dimensions of the disc. Thicker consistency adhesives, such as spreadable paste adhesives or thick putty-like adhesives may be ... |
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| Tomographic Reconstruction of Shallow Water Bubble Fields |
1999 |
29 pages |
| Authors:
Daniel Rouseff; Frank S. Henyey; Jerald R. Caruthers; Stephen J. Stanic; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| In the winter of 1997, a shallow water experiment was conducted near the Scripps Pier in La Jolla, California, USA. The goal was to determine the dynamics, distribution and acoustic effects of bubbles just offshore from active surf. A major component of the experiment was the "Delta Frame," an apparatus that supported two acoustic sources and eight receivers. Acoustic intensity was measured at frequencies between 39 ... |
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| Initial Structural-Acoustic Modeling and Control Results for a Full-Scale Composite Payload Fairing for Acoustic Launch Load Alleviation |
1999 |
15 pages |
| Authors:
Roger M. Glaese; Eric H. Anderson; CSA ENGINEERING INC PALO ALTO CA
|
| Launch loads, both mechanical and acoustic, are the prime driver of spacecraft structural design. Passive approaches for acoustic attenuation are limited in their low frequency effectiveness by constraints on total fairing mass and payload volume constraints. Active control offers an attractive approach for low frequency acoustic noise attenuation inside the payload fairing. Smart materials such as piezoceramics can be exploited as actuators for structural-acoustic control. In one active approach, structural ... |
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| Variable Store Flutter Suppression (AASERT 95) |
09 SEP 1998 |
25 pages |
| Authors:
Daniel J. Inman; VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF MECHANICAL ENGINEERING
|
| The objectives for this three year program where a) to design and develop mechanics models for a novel "large stroke" piezoceramic actuator, b) examine the usefulness of this actuator for solving the store induced flutter problem. In particular our goal has been to formulate predictive models that would be useful in the design and commercialization of such actuators. |
|
| Multiple Scatter Theory of Ocean Sediments II |
16 JAN 98 |
48 pages |
| Authors:
Nicholas P. Chotiros; TEXAS UNIV AT AUSTIN APPLIED RESEARCH LABS
|
| It is postulated that a laminar sand bed may be modeled as an ensemble of randomly layered poroelastic material. The thickness of each layer was related to the associated grain size and porosity by a conservation of mass relationship. The effect of lateral variations in grain size were simulated by performing a coherent ensemble average of results from several realizations of the randomly stratified medium. Poroelastic medium parameters were chosen ... |
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| Finite Difference Modelling of Scattering by Objects in the Seabed |
JUL 96 |
45 pages |
| Authors:
J. A. Fawcett; J. L. Grimbergen; SACLANT UNDERSEA RESEARCH CENTRE LA SPEZIA (ITALY)
|
| In this report we describe the theory and some implementation issues of a finite difference code used at SACLANT Centre. In particular, we consider the modelling of attenuation and the excitation of a remote incident field by using Huygen's sources. A series of comparisons of finite difference results with analytical results is performed. The report concludes with a series of computations of scattering of a generalized plane wave from a ... |
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| Transducer Design Experiments for Ground-Penetrating Acoustic Systems |
19 MAR 1996 |
17 pages |
| Authors:
E. G. Eckert; J. W. Maresca Jr; VISTA RESEARCH INC MOUNTAIN VIEW CA
|
| The transmission of impulsive acoustic signals into a homogeneous soil medium was investigated. Measurements performed using a piezoelectric driver and a hydrophone as the acoustic sources demonstrate that both types of transmitters (positioned at the air soil interface) are capable of producing acoustic waves in soil. The relative strength of the acoustic signals produced by each source was found to be approximately equal. The angular ... |
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| Active Structural Acoustic Control (ASAC) |
01 MAR 96 |
81 pages |
| Authors:
Chris R. Fuller; VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF MECHANICAL ENGINE ERING
|
| This final report for the Office of Naval Research Grant NOOOl4-92-J- 117O concerns further VPI&SU research to develop and refine active structural acoustic control (ASAC) with active/adaptive structures. The focus is on the development and demonstration of advanced system design and optimization techniques for complex structures and disturbances, and realistic system implementations. This required a highly coordinated analytical and experimental research effort in the three areas of structural acoustics, actuators ... |
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| Assessment of Noise Levels in and Around the Sikorsky S-7OA-9 Black Hawk Helicopter |
FEB 96 |
|
| Authors:
R. B. King; A. J. Saliba; D. C. Creed; J. R. Brock; DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)
|
| This document reports the results of a comprehensive noise survey of the Sikorsky S-7OA-9 Black Hawk helicopter environment and provides an assessment of the hearing protection devices worn by personnel exposed to this environment. Ambient noise levels were measured in the cabin of the Black Hawk at four positions under various flight conditions and at thirteen positions outside the Black Hawk under various ground running conditions. The attenuation properties of ... |
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| Control of Structural Vibrations by Vorticity Production |
FEB 96 |
161 pages |
| Authors:
Michael S. Howe; BOSTON UNIV MA COLL OF ENGINEERING
|
| Analytical models are investigated of the damping of sound and structural vibrations by vorticity production in the apertures of bias flow and grazing flow perforated elastic plates. A generalized bending wave equation is formulated for a plate perforated with an homogeneous distribution of small apertures, and is used to predict the attenuation of sound and resonant bending waves. The results depend on the Rayleigh conductivity of an aperture in a ... |
|
| Active Structural Acoustic Control (ASAC). Appendix C |
01 AUG 95 |
595 pages |
| Authors:
Chris R. Fuller; VIRGINIA POLYTECHNIC INST AND STATE UNIV BLACKSBURG DEPT OF MECHANICAL ENGINE ERING
|
| This final report for the Office of Naval Research Grant NOOOl4-92-J- 117O concerns further VPI&SU research to develop and refine active structural acoustic control (ASAC) with active/adaptive structures. The focus is on the development and demonstration of advanced system design and optimization techniques for complex structures and disturbances, and realistic system implementations. This required a highly coordinated analytical and experimental research effort in the three areas of structural acoustics, actuators ... |
|
| Naval Undersea Warfare Center Division Newport Technical Digest. Structural Acoustics |
JUN 95 |
115 pages |
| Authors:
Richard H. Nadolink; Ding Lee; James C. Meng; Albert H. Nuttall; Norman L. Owsley; NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV RI
|
| The theme of this issue of the Naval Undersea Warfare Center Division Newport's Technical Digest is structural acoustics and composite structures. Structural acoustics is that field of physics dealing with the propagation of time-wise varying motion in solid bodies and their interaction with acoustic media. The practical application of structural acoustics is in noise control. The problems in this area of engineering science are complex because, unlike acoustic fluids, there ... |
|
| Simulation of Acoustic Multipath Arrival Structure in the Middle Atlantic Bight |
JUN 95 |
79 pages |
| Authors:
Glen E. Kaemmerer Jr; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| In support of the Mid-Atlantic Bight Field Study process studies to be conducted in July 1996 and February 1997, a feasibility study and simulation of the acoustic multipath arrival structure was conducted. The feasibility study consisted of a literature search of oceanographic, geophysical and climatological data to create an accurate model of the Middle Atlantic Bight. This model was used to predict transmission losses and signal-to-noise ratios expected during the ... |
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| Sound Attenuation and Speech Intelligibility of a Modified Active Noise Reduction (ANR) Headset for Use by P3-C Sensor Operators |
MAY 95 |
33 pages |
| Authors:
C. E. Williams; D. W. Maxwell; G. B. Thomas; NAVAL AEROSPACE MEDICAL RESEARCH LAB PENSACOLA FL
|
| Sound attenuation and speech intelligibility evaluations were conducted on a modified active noise reduction (ANR) headset being considered for use by sensor operators in Navy P3-C aircraft. Measurements were obtained on 10 male ensigns in the Naval Aviation Flight Training Program. A comparison of the sound attenuation values obtained with the ANR on (combined passive and active attenuation) to values obtained with the ANR off' (passive attenuation) revealed 10-15 (B ... |
|
| Mode Coupling in Shallow Water Acoustic Propagation |
26 APR 95 |
109 pages |
| Authors:
Robert I. Odorn; James A. Mercer; UNIV OF WASHINGTON SEATTLE APPLIED PHYSICS LAB
|
| Characterization of sound propagation in shallow water requires a detailed understanding of the propagation processes and environmental properties, and how they are linked. This report contains three separate sections that address the effects of range dependence, sediment transverse isotropy, and high attenuation on acoustic propagation in shallow water. The investigations described are theoretical and numerical, and are based on the method of coupled local modes. (AN) |
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| Composite Smart Materials for Defense and Dual-Use Applications |
12 APR 95 |
7 pages |
| Authors:
Stphen R. Winzer; MARTIN MARIETTA LABS BALTIMORE MD
|
| During the past four months, we have: *Set up the program, *Conducted a kick-off meeting, *Made substantial progress on Task 1 (Requirements Definition for Undersea Quieting), *Initiated parts of Task 2 (Preliminary Material Requirements Definition), *Presented two papers, one at the SPIE meeting in San Diego, CA, and one at the ONR Transducer Materials and Transducers Workshop, Pennsylvania State University. (MM) |
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| Acoustically Quiet, Passive Load for Testing Low-Speed Motors. |
11 APR 1995 |
|
| Authors:
Richard F. Santopietro; Gregory J. Majewski; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| The load absorbing device is housed in a fluid filled housing for cooling and vibration damping purposes. The device includes a rotating disc coupled to the motor output shaft, and brake calipers for engaging the disc periphery to incrementally increase the torque load on the motor. A support structure shields these components and serves as the support for the motor to be tested. Vibration isolating mounts are used to support ... |
|
| Materials for Adaptive Structural Acoustic Control. Volume 4 |
06 APR 95 |
126 pages |
| Authors:
PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS RESEARCH LAB
|
| The objectives of this ONR sponsored University Research Initiative (URI) entitled "Materials for Adaptive Structural Acoustic Control" concern both basic fundamental studies and highly applied development of the piezoelectric and electrostrictive ferroelectric ceramics which carry both the sensing and actuation functions for adaptive control. The report documents work over the third year of this five year program. For convenience and continuity, the activities are grouped under the headings General Summary ... |
|
| Materials for Adaptive Structural Acoustic Control. Volume 3 |
06 APR 95 |
206 pages |
| Authors:
L E. Cross; PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS RESEARCH LAB
|
| The objectives of this ONR sponsored University Research Initiative (URI) entitled "Materials for Adaptive Structural Acoustic Control" concern both basic fundamental studies and highly applied development of the piezoelectric and electrostrictive ferroelectric ceramics which carry both the sensing and actuation functions for adaptive control. The report documents work over the third year of this five year program. For convenience and continuity, the activities are grouped under the headings General Summary ... |
|
| Materials for Adaptive Structural Acoustic Control. Volume 2 |
06 APR 95 |
208 pages |
| Authors:
L. E. Cross; PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS RESEARCH LAB
|
| The objectives of this ONR sponsored University Research Initiative (URI) entitled "Materials for Adaptive Structural Acoustic Control" concern both basic fundamental studies and highly applied development of the piezoelectric and electrostrictive ferroelectric ceramics which carry both the sensing and actuation functions for adaptive control. The report documents work over the third year of this five year program. For convenience and continuity, the activities are grouped under the headings (General Summary ... |
|
| Materials for Adaptive Structural Acoustic Control. Volume 1 |
06 APR 95 |
214 pages |
| Authors:
L E. Cross; PENNSYLVANIA STATE UNIV UNIVERSITY PARK MATERIALS RESEARCH LAB
|
| The objectives of this ONR sponsored University Research Initiative (URI) entitled "Materials for Adaptive Structural Acoustic Control" concern both basic fundamental studies and highly applied development of the piezoelectric and electrostrictive ferroelectric ceramics which carry both the sensing and actuation functions for adaptive control. The report documents work over the third year of this five year program. For convenience and continuity, the activities are grouped under the headings General Summary ... |
|
| Sound Attenuation Evaluation of the Navy's HGU-84/P Helicopter Helmet |
JAN 95 |
18 pages |
| Authors:
D. W. Maxwell; C. E. Williams; NAVAL AEROSPACE MEDICAL RESEARCH LAB PENSACOLA FL
|
| First article sound attenuation tests were conducted on samples of the HGU-84/P helicopter helmet, candidate replacement for the SPH-3C series of helmets, supplied for evaluation by the Naval Air Warfare Center Aircralt Division, Warminster, Pennsylvania. The tests were conducted in accordance with American National Standard ANSI 512.6-1984, Method for the Measurement of Real- Ear Attenuation of Hearing Protectors. Objective measurements of attenuation, microphone-in-real-ear (MIRE), were also obtained for database and ... |
|
| Theoretical Estimates of High Frequency Acoustic Attenuation and Backscattering from Suspended Sand Particles in the Ocean and in an Estuary |
NOV 94 |
|
| Authors:
R. A. Thuraisingham; DEFENCE SCIENCE AND TECHNOLOGY ORGANIZATION CANBERRA (AUSTRALIA)
|
| Theoretical estimates of high frequency sound attenuation and backscattering strengths from suspended sand particles in the ocean and in an estuary are given. The estimates are obtained using the measured volume concentrations of suspended particle in the upper layers of the ocean, from the particle size spectra near the clear water minimum, and from measurements of suspended sediments at different depths from the bottom of an estuary. Estimates are given ... |
|
| Determination of Multiple Sound Sources |
31 AUG 94 |
11 pages |
| Authors:
William A. Yost; Stanley Sheft; Raymond Dye; LOYOLA UNIV OF CHICAGO IL PARMLY HEARING INST
|
| The results studied showed that the SALT procedure produced weights that were much more consistent with subject reports than threshold measures. That is, the change in weights with increasing stimulus duration for the lateralization task indicated that the tones become more separable (analytic listening) as the overall duration increases. This does not occur with traditional measures of thresholds. In the amplitude modulation task, the modulated tones become more separable (analytic ... |
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| Acoustic and Vibration Attenuation Composite Material. |
09 AUG 1994 |
|
| Authors:
Usman A. Sorathia; Joseph W. Killian; Andrew W. Jarrett; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| The present invention relates to acoustic and vibration attenuation composite material, particularly to damping tiles of the Type VI class 1, suitable for use in aircraft, ship and submarine applications, that is inexpensive, does not result in an unacceptable weight penalty, and is conformable-in-place to complex curvatures. The present acoustic and vibration attenuation composite comprises a constraining layer of at least one ply of graphite fabric together with curable phenolic ... |
|
| Cascade Orificial Resistive Device. |
12 JUL 1994 |
|
| Authors:
Nicholas Bitsakis; James Cassidy; DEPARTMENT OF THE NAVY WASHINGTON DC
|
| A cascade orificial resistive device for throttling fluid flow which minimizes acoustic noise and internal vibrations is described herein. The device has a hollow body defining a fluid passageway, a plurality of perforated plates mounted within the passageway, a fixed end ring adjacent one end of the perforated plates, and a threadable end ring adjacent an opposite end of the perforated plates to place the plates in compression. Each of ... |
|
| Noise Level Reduction of .50 Caliber Gunfire by Terrain Shielding |
JUL 94 |
66 pages |
| Authors:
Larry L. Pater; Raman Yousefi; Walter Alvendia; CONSTRUCTION ENGINEERING RESEARCH LAB (ARMY) CHAMPAIGN IL
|
| Gunfire at Army rifle ranges is an unavoidable part of military training that can disturb the surrounding community and become a source of complaint. Barriers can effectively screen noise in some scenarios, and are useful in reducing noise from small arms fire because acoustic energy from this noise source is concentrated at relatively high frequencies, making barriers of modest size large in terms of wavelength and capable of providing significant ... |
|
| Passive Aero-Acoustic Sensor Self Interference Cancellation. Phase 1 |
23 APR 1994 |
80 pages |
| Authors:
Felix Rosenthal; J. C. Stevens; SIGNAL SEPARATION TECHNOLOGIES ANNANDALE VA
|
| Some Army HMMWV armored personnel carrier vehicles carry air-acoustic sensor systems comprised of a complement of roof-mounted microphones to detect and identify other vehicles and aircraft such as helicopters. The performance of these systems tends to become degraded as a result of the vehicle's own engine and road noise. Multi-channel noise cancellation, if correctly applied, is capable of removing most of the own-vehicle's engine self noise from the microphone outputs. ... |
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| Sensitivity of Shallow Water Transmission Loss to Source and Receiver Proximity to a Hard Bottom Under Downward Refracting Conditions |
16 DEC 93 |
17 pages |
| Authors:
Peter D. Herstein; Bernard F. Cole; David G. Browning; William G. Kanabis; NAVAL UNDERSEA WARFARE CENTER NEWPORT DIV RI
|
| Under downward refracting conditions, raypaths from a shallow source will tend to have grazing angles at a hard bottom that are greater than the critical angle arid, therefore, suffer a relatively large loss per bounce . As the source depth increases, lower grazing angles can be obtained. When the grazing angle becomes less than the critical angle, bottom loss per bounce is significantly reduced, allowing a possible reduction in propagation ... |
|
| An Evaluation of a Tactical Active Multi-Environment Acoustic Prediction System versus Measured Data |
SEP 93 |
70 pages |
| Authors:
Robert E. Coleman; NAVAL POSTGRADUATE SCHOOL MONTEREY CA
|
| This thesis evaluates the capabilities of MAPS ( Multi-Environment AIM (Acoustic Interference Monitor) Prediction System) to determine if the system can accurately predict shallow water propagation loss. SHAREM 102 produced real world propagation loss data from the Gulf of Oman that was used to conduct comparison runs using MAPS. It was found that MAPS was an accurate, user friendly, tactical decision aid for littoral shallow water predictions. MAPS Vs Measured ... |
|
| Investigation of a Fibre Optic Frequency Shifter and Optical Isolator |
30 APR 93 |
84 pages |
| Authors:
Walter Johnstone; Graham Thursby; Craig Michie; STRATHCLYDE UNIV GLASGOW (UNITED KINGDOM) DEPT OF ELECTRONIC AND ELECTRICAL ENGINEERING
|
| This report documents a programme of investigation of an in line fibre optic frequency translator and optical isolator on behalf of AFOSR (90- 0286). The proposed designs are based on evanescent field coupling from a single mode optical fibre to a multi-mode planar waveguide overlay. The programme focused mainly on the development of a particular design of frequency translator and included extensive characterization of fibre optic overlay structures in general. ... |
|
| Sound Attenuation Characteristics of the Standard DH-132A and SPH-4 Helmets Worn in Combination with Standard Issue Earplugs |
JAN 93 |
19 pages |
| Authors:
Ben T. Mozo; Linda S. Barlow; Barbara A. Murphy; ARMY AIR MOBILITY RESEARCH AND DEVELOPMENT LAB FORT EUSTIS VA EUSTIS DIRECTOR ATE
|
| The Health Hazard Assessment (HHA) of Army systems usually requires a review of noise and hearing protection associated with the systems used. Hearing protection for crews in combat vehicles is specified to be the DH-132A and, in some cases where noise levels are extremely high, earplugs are worn in combination with the helmet in order to provide adequate protection. Hearing protection for Army helicopter crewmembers is the SPH-4 helmet with ... |
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| Shallow Water Sediment Properties Derived from High-Frequency Shear and Interface Waves |
10 APR 92 |
|
| Authors:
John Ewing; Jerry A. Carter; George H. Sutton; Noel Barstow; WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
|
| Low-frequency sound propagation in shallow water environments is not restricted to the water column but also involves the subbottom. Thus, as well as being important for geophysical description of the seabed, subbottm velocity/ attenuation structure is essential input for predictive propagation models. To estimate this structure. bottom-mounted sources and receivers were used to make measurements of shear and compressional wave propagation in shallow water sediments of the continental shelf, usually ... |
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| Noise Reduction Using An Air-Permeable Ceiling |
1992 |
|
| Authors:
Wayne H. Bradley; ILLINOIS UNIV AT URBANA DEPT OF ELECTRICAL ENGINEERING
|
| A scaled (1 ft = 1 m) model of a German coffered ceiling and three variations were designed, built, and tested at Construction Engineering Research Laboratory in Champaign, II. To measure the efficiency of these ceilings, a scaled representation of the spectral range for small arms fire was radiated through the suspended models. The noise reduction measured for these models is compared to theoretical design curves ... |
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| The Effects of Attenuating Returning Echolocation Signals at the Lower Jaw of a Dolphin (Tursiops Truncatus) |
JUN 1991 |
10 pages |
| Authors:
Randall L. Brill; Patrick J. Harder; NAVAL COMMAND CONTROL AND OCEAN SURVEILLANCE CENTER RDT AND E DIV SAN DIEGO CA
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| Recordings were made during an echolocation experiment in order to observe any changes in the parameters of outgoing signals as a function of the deliberate attenuation of returning signals at the lower jaw of a dolphin (Tursiops truncatus). A dolphin was conditioned to perform a discrimination task while wearing either of two rubber hoods covering its lower jaw in addition to performing the same task while wearing no hood. A ... |
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| Attenuation Produced by Foam Earplugs Worn by Chinchilla |
MAY 91 |
16 pages |
| Authors:
James H. Patterson Jr.; Ilia M. Lomba Gautier; Melvin Carrier Jr.; Dennis L. Curd; C. E. Hargett Jr; ARMY AEROMEDICAL RESEARCH LAB FORT RUCKER AL
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| This report documents the attenuation of modified foam earplugs when worn by chinchilla. Since the ear canal of the chinchilla is smaller than human, the earplugs were trimmed to a diameter of 7.2 mm. This provided a good fit to the chinchilla ear canal. Methods for determining the attenuation were adapted from ANSI standard methods for determining attenuation for humans. The average attenuation of the earplugs for the chinchilla was ... |
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Reports by Keyword(s)
*ACOUSTIC ATTENUATION
