Omkar Sharma

Noise emission levels in coal industry

Abstract The noise levels in coal washeries, coal preparation plants, open cast and underground mining centres are very high when compared to accepted limits for occupational noise exposure. Even the residual noise level when there is minimal activity is 80 to 82 dB. The results of the noise emitted by machines are analysed to predict an overall noise climate.

Characterisation of sound pressure levels produced by crackers

Abstract The study of the characterisation of crackers is undertaken to specify maximum sound pressure levels produced by crackers. It is observed that the sound pressure level produced by Indian crackers is higher than the accepted norms. It is also seen that there exists a simple relation between sound pressure level values measured in peak C-weighted, average impulse A-weighted and A-weighted sound exposure level. The data may help in fixing the choice of parameter to be adopted for instantaneous and multiple impulsive events.

A noise and vibration survey in an underground railway system

Abstract Noise and vibration measurements have been made in the rapid rail transit system (metro) in Calcutta. The track is 16·43 km long, is ballastless and has been laid for most of the journey in a specially-designed underground concrete tube of box structure. The results of measurement show that both noise and vibration levels are higher than the recommended values for reasonable comfort. The factors responsible for excessive noise have been analysed and methods to bring noise and vibration levels within comfortable limits have been suggested.

Design Considerations for Enhancing Sound Insulation Characteristics of Window Glazing for Traffic Noise Abatement

The work reviews the design aspects related to window glazing constructions for combating the low frequency noise radiated by vehicular traffic and assimilates them in a cause and effect diagram. An experimental investigation is conducted in Reverberation chambers on various window glazing configurations to ascertain the performance of various parameters viz., depth of air space and effect of lamination on sound insulation characteristics. A pronounced dip attributed to mass-air-mass resonance consistent with theoretical formulation is observed when air gap is less that 30 mm in double glazings. Significant increase in (Rw+Ctr) value is observed in a sandwich constructions with 85 mm air gap or in sandwich constructions with either one double glazing or both are double.

Sound absorption by conical absorbers and glasswool layer combination

Abstract The fact that the addition of a cone to a porous absorbent can increase the range of its absorption characteristics prompted the authors to investigate the possibility of using a cone and a certain layer of glasswool as a substitute for the traditional wedge structure for treatment in anechoic chambers. Although the combination can yield increased absorption in the low- and medium-frequency ranges, the drop in absorption at high frequencies limits its use as an ideal substitute for wedge structure. Yet the combination can give uniform high absorption for most noise and reverberation control applications.