Volume 120, Issue 2, August 2006
Index of content:
- NOISE: ITS EFFECTS AND CONTROL 
120(2006); http://dx.doi.org/10.1121/1.2213571View Description Hide Description
A mode-matching method is used to investigate the performance of a two-dimensional, modified reactive silencer. The modification takes the form of a membrane which is attached to the internal walls of the expansion chamber parallel to the axis of the inlet/outlet ducts. The height of the membrane above the level of the inlet/outlet ducts can be varied and, by this means, the device is tuned. It is shown that the stopband produced by the silencer can be broadened and/or shifted depending upon the height to which the membrane is raised. Attention is focused on the efficiency of the device at low-frequencies—the regime where dissipative silencers are usually least effective. The potential use of the device as a component in a hybrid silencer for heating ventilation and air-conditioning (HVAC) ducting systems is discussed.
120(2006); http://dx.doi.org/10.1121/1.2215219View Description Hide Description
The procedure for spatial sampling in order to find out the relation between and for urban noise is presented. From that data, other parameters like or can be easily obtained from values. To this end, a long-term measuring campaign was carried out in eight cities of different types and sizes in northeastern Spain. The statistical treatment of the measures was based on a characterization of the streets in view of their type, including factors such as traffic and land use, which enabled a final classification of six types of streets. The results show that streets of the same type located in different cities do not have the same value for -, due to socioeconomic factors, but analyzed city by city have a close to normal (or -Student) distribution. Under this behavior, it is demonstrated that a sample of between 14 and 25 points, depending on the city characteristics, is needed in order to calculate -, with a confidence level of 95% and a margin of error of .