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Designing for Spatial Sound in a Challenging Auditorium Restoration
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The early lateral energy fraction (LF) is one of the most important acoustic descriptors of concert hall sound. This paper describes a procedure for validating LF measurements of halls. The measurement of LF can be problematic due to uncertainties with calibrating, aligning and aiming two microphones of different sensitivities and directivity patterns. The validity and reproducibility of measured LF values needs to be established. A series of simulated sound fields consisting of the direct sound and a single reflection in an anechoic chamber were used to validate LF measurement systems. The reflection was varied in angle and level, and the measured LF values were compared with the known or calculated values. Two commercially available measurement systems were validated and the measured results were generally within one JND of the calculated values.
This paper describes experiments with simulated reflections in an anechoic chamber, in an attempt to understand the importance of early reflections in a concert hall. The subjective effects of a single side reflection were investigated; and the effect of “spatial impression” was identified as the predominant subjective effect. This “spatial impression” was produced for reflection delays between 10 and 80 msec by lateral rather than ceiling reflections.The variation in the degree of spatial impression for variations in different reflection parameters was investigated, as was the effect of two side reflections. It was concluded that the degree of spatial impression is probably related to the ratio of lateral to non-lateral sound arriving within 80 msec of the direct sound. Other authors' theories of the role of first reflections are discussed in the final sections of the paper. Results here gave support to the view that a cross-correlation process is involved in subjective spatial impression.
Abstract—Multiobjective evolutionary algorithms (EAs) that use nondominated,sorting and,sharing have been criti- cized mainly for their: 1),computational complexity (where,is the number,of objectives and,is the population size); 2) nonelitism approach; and 3) the need for specifying a sharing parameter. In this paper, we suggest a nondominated sorting-based multiobjective EA (MOEA), called nondominated sorting genetic algorithm II (NSGA-II), which alleviates all the above three difficulties. Specifically, a fast nondominated sorting approach with,computational complexity is presented. Also, a selection operator is presented that creates a mating pool by combining the parent and offspring populations and selecting the best (with respect to fitness and spread) solutions. Simulation results on difficult test problems show that the proposed NSGA-II, in most problems, is able to find much better spread of solutions and better convergence near the true Pareto-optimal front compared,to Pareto-archived evolution strategy and strength-Pareto EA—two other elitist MOEAs that pay special attention to creating a diverse Pareto-optimal front. Moreover, we modify the definition of dominance in order to solve constrained multiobjective problems efficiently. Simulation results of the constrained NSGA-II on a number of test problems, including a five-objective seven-constraint nonlinear problem, are compared with another constrained multiobjective optimizer and much better performance of NSGA-II is observed. Index Terms—Constraint handling, elitism, genetic algorithms, multicriterion decision making, multiobjective optimization, Pareto-optimal solutions.
The Christchurch Town Hall (2650 seats), which was opened in 1972, was designed primarily as a choral symphony hall. Reverberation time (125 Hz–2 kHz) in excess of 2.2 s with the hall full, is provided by a volume of 20 500 m3 and generally reflective surfaces. The basic design aim, audibility of early lateral reflections, is achieved by large interior oblique reflectors which hang in the space from the walls at about half‐ceiling height. They are, thus, within and independent of boundaries of the reverberant volume. The resulting temporal and spatial distribution of energy in the reflection sequences gives this hall an unusual combination of reverberance, envelopment, and clarity. Measurements of T60, T15, EDT, and integrated early energy are presented and discussed in explanation of the combination of reverberance and clarity experienced in the hall.
This paper reports the results of subjective studies to determine objective predictors of perceived listener envelopment in concert halls. Subjects, seated in an anechoic room, were exposed to simulated sound fields that were expected to have varied listener envelopment. As independent variables: the reverberation time, the early‐to‐late sound ratio, the overall sound level, and the angular distribution of the late‐arriving sound levels were varied. All of these factors had statistically significant effects on perceived listener envelopment. The results indicate, however, that the angular distribution of the late arriving sound and the overall level would have the largest effects in real concert halls. Thus listener envelopment depends on having strong lateral reflections arriving at the listener 80 ms or more after the direct sound. Several objective measures correlated significantly with listener envelopment. However, a new measure, the late lateral sound level, as measured using a figure‐of‐eight microphone, was found to be both conceptually simple and a very good predictor of the perceived listener envelopment of the sound fields in this experiment.
Multi-objective evolutionary algorithms which use non-dominated sorting and sharing have been mainly criticized for their (i) O(MN s) computational complexity (where M is the number of objectives and N is the population size), (ii) non-elitism approach, and (iii) the need for specifying a sharing parameter. In this paper, we suggest a non-dominated sorting based multi-objective evolutionary algorithm (we called it the Non-dominated Sorting GA-II or NSGA-II) which alleviates all the above three difficulties. Specifically, a fast non-dominated sorting approach with O(MN 2) computational complexity is presented. Second, a selection operator is presented which creates a mating pool by combining the parent and child populations and selecting the best (with respect to fitness and spread) N solutions. Simulation results on a number of difficult test problems show that the proposed NSGA-II, in most problems, is able to find much better spread of solutions and better convergence near the true Pareto-optimal front compared to PAES and SPEA two other elitist multi-objective EAs which pay special attention towards creating a diverse Pareto-optimal front. Moreover, we modify the definition of dominance in order to solve constrained multi-objective problems efficiently. Simulation results of the constrained NSGA-II on a number of test problems, including a five-objective, seven-constraint non-linear problem, are compared with another constrained multi-objective optimizer and much better performance of NSGA-II is observed. Because of NSGA-II's low computational requirements, elitist approach, parameter-less niching approach, and simple constraint-handling strategy, NSGA-II should find increasing applications in the coming years.
Applications of Machine Learning Bounding-Breps for Optimised Acoustical Reflectors
- J O'keefe
The influence of height/width ratio and side wall boxes on room acoustics measurements
- J Keefe