Volume 123, Issue 3, March 2008
Index of content:
- NOISE: ITS EFFECTS AND CONTROL 
123(2008); http://dx.doi.org/10.1121/1.2835608View Description Hide Description
The use of a single actuator tuned to an optimum impedance to control the sound power radiated from a turbulent boundary layer (TBL) excited aircraftpanel into the aircraft interior is examined. An approach to calculating the optimum impedance is defined and the limitations on the reduction in radiated power by a single actuator tuned to that impedance are examined. It is shown that there are too many degrees of freedom in the TBL and in the radiation modes of the panel to allow a single actuator to control the radiated power. However, if the panel modes are lightly damped and well separated in frequency, significant reductions are possible. The implementation of a controller that presents a desired impedance to a structure is demonstrated in a laboratory experiment, in which the structure is a mass. The performance of such a controller on an aircraftpanel is shown to be effective, if the actuator impedance is similar to but not the same as the desired impedance, provided the panel resonances are well separated in frequency and lightly damped.
123(2008); http://dx.doi.org/10.1121/1.2828068View Description Hide Description
Geo-referenced close proximity rolling noise and sound absorptionmeasurements are used for acoustical characterization of asphalt concrete surfaces in an urban environment. A close proximity noise map of streets with low speed limits is presented for a reference speed of . Different pavements and pavement conditions, common in urban streets, are analyzed: dense and semidense asphalt concrete, with Spanish denomination D-8 and S-12, respectively, and on the other hand, dense pavement at the end of its service life . From the acoustics point of view, the most favorable surface, by more than compared with the S-12 mix, is the smoothest surface, i.e., the D-8 mix, even though it presents a minor absorption coefficient in normal incidence. Noise levels from dense surfaces (D-8) increase significantly over time, principally due to the appearance of surface defects such as cracks and ruts. Longitudinal variability of the close proximity tire/pavement noise emission and surface homogeneity are also analyzed.
The acoustic and visual factors influencing the construction of tranquil space in urban and rural environments tranquil spaces-quiet places?123(2008); http://dx.doi.org/10.1121/1.2831735View Description Hide Description
Prior to this work no structured mechanism existed in the UK to evaluate the tranquillity of open spaces with respect to the characteristics of both acoustic and visual stimuli. This is largely due to the fact that within the context of “tranquil” environments, little is known about the interaction of the audio-visual modalities and how they combine to lead to the perception of tranquillity. This paper presents the findings of a study in which visual and acoustic data, captured from 11 English rural and urban landscapes, were used by 44 volunteers to make subjective assessments of both their perceived tranquillity of a location, and the loudness of five generic soundscape components. The results were then analyzed alongside objective measurements taken in the laboratory. It was found that the maximum sound pressure level and the percentage of natural features present at a location were the key factors influencing tranquillity. Engineering formulas for the tranquillity as a function of the noise level and proportion of the natural features are proposed.