Acoustical effects of columns, beams and furniture on sound fields in small enclosures
In acoustic design of small enclosures, it is a considerably important matter to control eigenmodes at low frequencies, so that many researches have been done on the effect of overall shapes of rooms on the eigenmodes, such as optimization of room dimensions ratio. However, overall room shapes are usually restricted to rectangular forms due to easy construction, therefore it is desirable to improve sound fields only by changing partial elements in rectangular rooms. In the present paper, the effects of additional elements, such as columns, beams and furniture, on the sound field in a small rectangular room are investigated through wave-based numerical analysis. Supposing a room for listening use with a loudspeaker, the effects are evaluated regarding the flatness of frequency response and the uniformity of spatial distribution in a listening area. The results show that: the effect of columns is small but more than beams; that of closed-type shelves is relatively large but not so much as open-type shelves; the size and the arrangement of every element have unnegligible effects. It is also seen that the additional elements generally lead to positive effects in flatness of frequency response and special uniformity even at low frequencies, although in a specific case.
An investigation of the modal characteristics of nonrectangular reverberation rooms
The finite element method is used to study the modal characteristics of a class of reverberation rooms with parallel floors and ceilings. Special numerical procedures are developed to express acoustic finite element matrices as functions of room shape and to reduce the computational requirements for room evaluation. The modal distribution function proposed by Louden [M. M. Louden, Acustica 24, 101–104 (1971)] is used to evaluate room performance. Two studies of rooms with one nonparallel wall illustrate the typical influence of room shape on the modal distribution in the room. A global optimization is attempted for a room with five independent shape variables. A solution 40% better than the best rectangular reverberation room was found using approximately 450 000 room evaluations.
Marxism and Educational Theory: Origins and Issues
Introduction 1. The Development of Marxist Theory 2. The Development of Postmodernist Theory 3. The Sociological Context: The Place of Marxism and Postmodernism in Educational Theory 4. Postmodernism, Marxism and Educational Theory: A Critical Analysis 5. Postmodernism, Marxism and Educational Practice: A Critical Analysis 6. Globalization, Marxism and the Future of Education Conclusion