S.K. Tang

Performance of noise indices in office environment dominated by noise from human speech

Abstract An acoustical environment survey was carried out in six similar air conditioned landscaped offices in which human speech was considered to be the major source of complaint. Both questionnaire and physical noise measurement were administrated. Physical noise measurement data reveal higher sound energy within the human speech frequency range and high speech intelligibility level in the offices. Results also show that the preferred noise criterion gives good correlation with the auditory sensation comments of the office workers. The noise climate, the equivalent sound pressure level and the noise pollution level are also found to be useful in assessing the acoustical environment inside the surveyed offices.

On the application of active noise control in an open end rectangular duct with and without flow

Abstract The performance of the adaptive active control system in a relatively short open-end rectangular duct with and without air flow is investigated experimentally. Results show that the existence of broadband noise in the duct can reduce the sound attenuation level as high as 3 dB. Frequency range of the attenuation is also reduced by the broadband noise. The presence of air flow further reduces the performance of the system. It is found that the centre of the duct cross-section is suitable for error microphone location regardless the types of noise investigated. The effect of downstream position of error microphone on sound attenuation depends on the nature of the noise to be attenuated. Results also indicate that level of attenuation depends on the acoustic properties of the open end duct. The adaptive active control system in the present study is found to be not efficient at frequencies close to the duct eigen frequencies.

The effects of neighborhood views containing multiple environmental features on road traffic noise perception at dwellings

The importance of non-acoustical factors including the type of visual environment on human noise perception becomes increasingly recognized. In order to reveal the relationships between long-term noise annoyance and different types of neighborhood views, 2033 questionnaire responses were collected for studying the effect of perceptions of different combinations of views of sea, urban river, greenery, and/or noise barrier on the annoyance responses from residents living in high-rise apartments in Hong Kong. The collected responses were employed to formulate a multivariate model to predict the probability of invoking a high annoyance response from residents. Results showed that views of sea, urban river, or greenery could lower the probability, while views of noise barrier could increase the probability. Views of greenery had a stronger noise moderation capability than views of sea or urban river. The presence of an interaction effect between views of water and views of noise barrier exerted a negative influence on the noise annoyance moderation capability. The probability due to exposure to an environment containing views of noise barriers and urban rivers would be even higher than that due to exposure to an environment containing views of noise barriers alone.

Some characteristics of noise in air-conditioned landscaped offices

Abstract In the present study, noise measurements were carried out in 26 air-conditioned landscaped offices during lunch and office hours. The noise spectra show that, in general, the noise from office activities is of a frequency higher than 500 Hz. A-, B- and C-weighted sound levels are also calculated and it is found that linear relationships exist between these weighted levels. In addition, simple formulae are proposed for the estimations of noise criterion (NC) and noise rating (NR) from the A-weighted sound level which is also known as the equivalent sound pressure level. The air-conditioning systems affect the noise levels, NC and NR, but not the basic relationships between weighted sound levels, NC and NR.