Index of content:
Volume 108, Issue 3, September 2000
- NOISE: ITS EFFECTS AND CONTROL 
European methodology for testing the airborne sound insulation characteristics of noise barriers in situ: Experimental verification and comparison with laboratory data108(2000); http://dx.doi.org/10.1121/1.1286811View Description Hide Description
In the frame of the 1994–1997 Standard, Measurement and Testing program, the European Commission funded a research project, named Adrienne, to define new test methods for measuring the intrinsic characteristics of road traffic noise reducing devices in situ. The research team produced innovative methods for testing the sound reflection/absorption and the airborne sound insulation characteristics of noise barriers. These methods are now under consideration at CEN (European Committee for Standardization), to become European standards. The present work reports a detailed verification of the test method for airborne sound insulation over a selection of 17 noise barriers, representative of the Italian and European production. The samples were tested both outdoors, using the new Adrienne method, and in laboratory, following the European standard EN 1793-2. In both cases the single number rating for airborne sound insulation recommended by the European standard was calculated. The new method proved to be easy to use and reliable for all kinds of barriers. It has been found sensitive to quality of mounting, presence of seals, and other details typical of outdoor installations. The comparison between field and laboratory results shows a good correlation, while existing differences can be explained with the different sound fields and mounting conditions between the outdoor and laboratory tests. It is concluded that the Adrienne method is adequate for its intended use.
108(2000); http://dx.doi.org/10.1121/1.1287707View Description Hide Description
A time-domain computational approach is applied to investigate the behavior of perforated tube silencers at high sound levels. The one-dimensional computational technique employs a lumped parameter model for the perforate flows. The lumped parameter perforate model is based on time-invariant approximations for the equivalent length and resistance R, consistent with the use of a nonlinear perforate impedance. Empirical expressions for and R are developed experimentally using nondimensional scaling parameters. The model is applied to geometries representative of automotive resonators and multiple-duct mufflers. Conditions are simplified from those in an actual automotive system by considering single-frequency excitation and zero mean flow. Simulations with linear perforate behavior are compared to experimental data obtained with an extended impedance tube system. Simulations with nonlinear perforate behavior for one concentric tube resonator are compared to published experimental data.
Interference from degraded auditory stimuli: Linear effects of changing-state in the irrelevant sequence108(2000); http://dx.doi.org/10.1121/1.1288412View Description Hide Description
Cognitive performance, particularly on a number of tasks involving short-term memory for order, is impaired by the mere presence of irrelevant background sound. The current study examines the features of the irrelevant sound that determine its disruptive potency. Previous research suggests that the amount of variability in an irrelevant stream is related to the degree of disruption of memory. The present experiments used a parametric approach to manipulate degree of change more precisely. Increasing levels of degradation, effected either by low-pass filtering (speech) or by digital manipulation (speech and nonspeech), monotonically decreased the degree of interference. The findings support the following propositions: (i) the degree of physical change within an auditory stream is the primary determinant of the degree of disruption; and, (ii) the effects of irrelevant speech and irrelevant nonspeech sounds are functionally similar.