Showing papers in "Noise Control Engineering in 1981"
70 citations
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TL;DR: In this article, Resonant-cavity parallel baffles, either empty or with a thin absorbent lining, have been investigated as an alternative to fiberglass-filled baffles commonly used to control noise emission from large ducts.
Abstract: Resonant-cavity parallel baffles, either empty or with a thin absorbent lining, have been investigated as an alternative to fiberglass-filled baffles commonly used to control noise emission from large ducts. A method for predicting silencer attenuation is described, and it is shown that the new type of baffle is characterized by an acoustic performance similar to that of fibrous baffles, while being virtually immune to such problems as clogging, erosion, or settling. The emphasis of the study is on insertion loss measurements in a 7 by 10 ft wind tunnel.
10 citations
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TL;DR: In this paper, the theoretical background to the measurement of sound energy flow generated by transient sources, such as impact machines, is presented and various means of implementing the estimation process are discussed and reference will be made to the problems of field measurement.
Abstract: The theoretical background to the measurement of sound energy flow generated by transient sources, such as impact machines, will be presented. Various means of implementing the estimation process will be discussed and reference will be made to the problems of field measurement. Results of measurements made on a drop forge and other impulsive sources will be presented. It will be shown that directly radiated and reverberant sound can be satisfactorily separated.
6 citations
TL;DR: In this paper, the exhaust flow of many gas-powered machines consists of a series of distinct pulses and the sound field around the pulsed jet has been measured in the free-field conditions.
Abstract: The exhaust flow of many gas-powered machines consists of a series of distinct pulses. This non-steady jet flow has been studied experimentally by use of a simple pulse jet generator in which a rotating valve interrupts a flow of air. The valve porting was chosen to simulate the exhaust cycle of a pneumatic percussive drill and the noise produced by the generator is similar to that of a drill exhaust. The sound field around the pulsed jet has been measured in the free-field conditions.
6 citations
TL;DR: In this paper, the use of surface intensity measurements as an alternative to the conventional selective-wrapping technique of noise source identification and ranking on diesel engines was investigated, and the results demonstrated that the surface intensity method is a viable alternative for the selective wrapping technique.
Abstract: The use of surface intensity measurements as an alternative to the conventional selective‐wrapping technique of noise source identification and ranking on diesel engines was investigated. A six‐cylinder, in‐line, turbocharged, 350 horsepower diesel engine was used. Sound power was measured under anechoic conditions for eight separate parts of the engine at steady‐state operating conditions using the conventional technique. Sound power measurements were repeated on five separate parts of the engine using the surface intensity technique at the same steady‐state operating conditions. The results were compared by plotting sound power level against frequency, overall sound power level, and noise source rankings for the two methods. A specialized piston‐tube experiment was developed to alleviate the phase shift problems encountered with the surface intensity method by earlier researchers. The results of the experiments demonstrate that the surface intensity method is a viable alternative to the selective‐wrappi...
TL;DR: In this article, a duct lining with two layers of perforated sheeting and a gas-filled honeycomb core was selected for attenuating drive-fan noise in the National Transonic Facility.
Abstract: Noise control in the National Transonic Facility - a cryogenic wind tunnel - has been examined in terms of acoustical design criteria, drive-fan noise and exhaust system noise. A duct lining with two layers of perforated sheeting and a gas-filled honeycomb core was selected for attenuating drive-fan noise. With the exception of attenuation peaks, attenuation of the lining was found to experimentally agree with predicted values at 20 C air temperatures. Exhaust system noise will be attenuated with a large muffler used in conjunction with a 6.1-m high acoustical enclosure. Fan noise from the fan-ejector system will be attenuated by fan silencers and the acoustic enclosure.
TL;DR: In this article, the transfer of structureborne sound from a ship-like steel structure to cabin bulkheads has been investigated for three types of bulkhead material: chipboard, plastic faced calcium silicate and steel plates sandwiching a rock wool core.
Abstract: In the laboratory the transfer of structureborne sound from a ship-like steel structure to cabin bulkheads has heen investigated for three types of bulkhead material: chipboard, plastic faced calcium silicate and steel plates sandwiching a rock wool core. The most relevant results of the investigations are discussed: the influence of the applied materials for bulkheads and ceiling on the resulting sound pressure level in the cabin, the effect of the installation of a floating floor and the effect of the presence of a porthole. Estimates are given for the attainable insertion losses of floating floors on hoard ships.