Noise Control Treatments Research Articles

Noise control considerations in the modernization of a Boston subway station

The primary concern in the modernization program for the Park Street subway station was the intense wheel squeal on the sharply curved tracks (radii as small as 45 ft) at one end of the upper platform. Secondary concerns are reduction of the exposure of patrons to rolling and braking noise on the upper and lower levels. Measurements of existing acoustical conditions and typical noise levels of trains are described. The noise control treatments presently being installed and the anticipated reductions will be discussed. The practical performance characteristics required of acoustical materials for subway stations will also be summarized.

Results of a design effort to control building HVAC equipment noise

An Acoustical Society paper [J. Acoust. Soc. Am. 54, 273(A) (1973)] delivered in Boston on 10 April 1973 discussed the noise control design for a building requiring the exterior installation of its major mechanical and electrical equipment. Our primary concern was noise impact from three aircooled chillers, a transformer, and an emergency engine-generator located in an open outdoor equipment yard across the street from a quiet residential neighborhood. This study was particularly note-worthy because of the extensive interaction required between the architect, mechanical and electrical engineer, mad acoustical consultant. The systems configuration engineered by our firm two years ago is now in operation. For the major equipment we compare our predicted noise levels to the measured noise levels, both nearfield and in the community. We also appraise community opinion to the new noise source, and compare it to our predicted community response. Costs information for the noise control treatment is also presented.

Control of road noise by vehicle design

The task of reducing the noise emitted by commercial vehicles is complicated; not only are the mechano-acoustic aspects complex but there are serious commercial limitations arising from the cost of noise reduction in a very competitive industry. Noise radiated by the engine is the principal source on present-day commercial vehicles. The principles of design of enclosures to attenuate the noise are presented. The work of vehicle noise reduction is illustrated by an example in which the effects of exhaust silencing and various designs of engine enclosure are illustrated. It is concluded that it is possible, but not necessarily practicable, to get down to an I.S.O. test level of about 80 dBA with the appropriate amount of engine enclosure at a weight penalty of 9 Ib/dBA. However, space limitations on vehicles fitted with larger engines than those used in this work may make the fitting of an enclosure extremely difficult, and may necessitate considerable redesign of the vehicle. 80 dBA is probably the lower limit of commercial vehicle nosie and is set by type rolling noise. The vehicle manufacturer can make use of the techniques described above to make vehicles considerably quieter, but any acoustical treatment involves penalties in weight, cost, space, etc. For this reason it is cheaper and more effective to plan noise control treatments at the design stage than it is to modify existing vehicles.

Electroacoustic Transducer Efficiency of R, L, and C Components

It has long been recognized that electrical components under ac excitation behave as electroacoustic transducers (e.g., thermophone, transformer). The development of high-frequency power supplies for microminiaturized electronic packaging revived interest in resistors, inductors, and capacitors as sources of acoustical noise. The sound-power levels of 3 types of resistors, 3 types of inductors, and 4 types of capacitors were measured in a 0.75-m3 a reverberation chamber. Each component was excited by 13-octave bands of noise in the frequency range 1–16 kcps. From the PWL data and the input electrical power, the transducer efficiency and the average mean-square sound pressure at a distance of 1 m in a free field were determined. At 4 kcps, the efficiencies are approximately 10−14, 10−9, and 10−8 for representative R, C, and L components, respectively. For some C and L components, the sound pressures were sufficiently high to require noise-control measures. The effectiveness af various noise-control treatments (e.g., capsulation, potting) was evaluated.

Sound control for gas turbine package power plants.

Abstract The Gas Turbine Package Power Plant is a self-contained generating unit capable of 11,250 Kw. Designed for emergency, stand-by power it is being installed in residential areas. This article presents results of acoustical measurements before and after treatment for noise control. The breaking down of the complex sound source into individual components and treating each item individually provided a successful solution.

Noise Control Treatment for a 15-Passenger Commercial Helicopter

In 1955 a noise measurement and noise reduction study was carried out on a military model H-21 helicopter. Based on this study, two commercial versions of this helicopter were constructed early in 1957 by the Vertol Aircraft Corporation for the French Government for use in the recent International Air Exposition in Paris. This paper presents the noise control treatments contained in the commercial helicopters and compares inside noise levels before and after the treatment. The noise reduction achieved by the treatment in the passenger cabin averages approximately 5 db in the low-frequency octave bands and 20–25 db in the high-frequency octave bands. The resulting noise levels inside the completed helicopters are comparable to those of commercial fixed-wing airliners.