The purpose of this study was to investigate the feasibility of measuring the insertion loss (attenuation) provided by cannon earplugs using the Knowles Electronics Manikin for Acoustic Research. Five earplugs were tested in a 90 dB sound field at discrete frequencies matching those published by NIOSH. Each plug was exposed to 10 trials. Results indicate an approximation between values obtained in the study and NICSH published values. Some consistent differences tend to indicate that NIOSH values may overrate low frequency attenuation.

Noise, that undesirable portion of the ever-present sounds of our environment, has until the last decade, been considered as an unavoidable by-product of our rapid population growth and its accompanying mechanization. As awareness of adverse health effects from noise exposure grew, the Federal government, as protector of the public health and welfare, took the initial steps to control noise pollution. Federal legislation, beginning with the Clean Air Amendments of 1970, has been promulgated to control major offenders and to assist State and local governments in their endeavors to provide the public with an environment free from harmful noise levels. This paper first discusses sound and noise, the methods for describing and quantifying noise, and levels needed for protection. Secondly, control and abatement efforts are discussed with emphasis on legislated goals, the role of the Environmental Protection Agency, and State and local actions.

This report explains the development of a sound measuring system for continuous monitoring of sound levels. Dedicated telephone lines are used for data transmission so that sound level data can be monitored at installations far from the area of concern. This allows the sound sensing equipment to be left unattended and thereby greatly reduces the manpower costs of operation. That predetermined data conditions can be detected when they occur and corrective action can be taken immediately at the data receiving installation further justifies the method used. Background information and general need for such a system are discussed. Growing public concern with noise is creating a demand for more and better sound measurement devices and for more control of unnecessary noises. For description, the system is divided into functional sections. The sections are described and design considerations are given in order of data flow starting with the sound sensing devise, or microphone, and ending with the warning system which alerts the operator when a predetermined signal level has been exceeded. Circuits to detect selected conditional of excess sound and to control the alarm to these conditions are included.

No

Weight is a critical parameter in the design of any system launched into space. Current launch costs are on the order of 10,000 dollars per pound of payload capacity. Reducing weight and thus increasing payload capacity is always in the forefront of the design process. One method of increasing the payload capacity of launch vehicles is to reduce the acoustic environment in the interior of the fairing. A major problem is that passive methods currently used for noise suppression do not exhibit significant energy dissipation at low frequencies. This motivates the use of active noise control. Using active noise control for frequencies below 200 to 300 Hz in addition to the passive control means has potential to provide broadband noise suppression and thus a smoother, cheaper ride for any payload. The problem with this technique is that active noise control commonly uses electromagnetic speakers as the control element. The weight of the speaker adds more cost to the application due to the approximate cost per pound to send a launch vehicle and payload to space. At 10,000 dollars per pound of payload capacity, the added cost spent on protecting the payload can potentially reduce the amount of payload capacity a customer receives due to monies spent on non-payload mass. Therefore, necessity dictates a light weight noise control solution. This work investigates the feasibility of a transducer with less mass than that of a conventional loudspeaker which dissipates energy at the acoustic resonances of an enclosed cavity. The test setup involves using the transducer to lower the sound pressure levels of acoustic resonances which are excited by an external source, thus simulating the launch phase of a launch vehicle. The transducer is used as an actuator to add damping through feedback control. The transducer is comprised of three thin flexures that are actuated by piezoceramic material attached to both sides. The flexures actuate a speaker cone that is attached to the end of the flexures. The transducer can act as a sensor or an actuator due to the nature of the piezoceramics. The sound absorbing transducer is modeled to couple to the first acoustic resonance of a six foot cylindrical cavity. The cavity acts as a simplified model of a launch vehicle payload fairing. Equations of motion are derived to model actuator motion and the acoustic impedance of the cavity. A state-space model of the system was derived for two cases: a collocated sensor/actuator pair exciting the tube and an external source exciting the tube with the transducer acting as an absorber. The transducer is designed to affect the first mode, however damping is noticed in the next acoustic resonance. Analysis of the theoretical model indicated up to 70 percent reduction of the open-loop RMS values or a reduction of 10 dB. Experimental results with the optimized transducer produced a 35 percent reduction of the open-loop RMS value or 3.73 dB. The first acoustic resonance coupled well with the first structural mode of the transducer providing optimal noise suppression for the first mode. Damping was also noted in the second acoustic mode. Neglecting the inertia of the tip mass introduced errors in the predictions of the transducer resonances at higher frequencies. This problem limited the ability to control the higher modes of the cavity. / Master of Science

Thesis (M. Sc.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 90-92).

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

No description available.

No description available.

Approved for public release; distribution is unlimited. / The use of higher-order statistics provides insight into signals which is not always available at lower orders. Additionally, Gaussian-distributed signals have the interesting characteristic of disappearing at higher orders. Because so much of the noise and inter- ference environment is Gaussian-distributed, higher-order statistics thus offer the promise of an additional method of noise reduction and interference mitigation. As communica- tions signals become more and more complex, any additional ability to reduce the effects of noise and interference will have a profound impact on communications, surveillance, and intelligence systems. / US Department of Defense author (civilian).