Authors: Poletti, Mark A.
The theory of recording and reproduction of three-dimensional sound fields based on spherical harmonics is reviewed and extended. Free-field, sphere, and general recording arrays are reviewed, and the mode-matching and simple source approaches to sound reproduction in anechoic environments are discussed. Both methods avoid the need for both monopole and dipole loudspeakers—as required by the Kirchhoff–Helmholtz integral. An error analysis is presented and simulation examples are given. It is also shown that the theory can be extended to sound reproduction in reverberant environments.
Authors: Orfanidis, Sophocles J.
A family of digital parametric audio equalizers based on high-order Butterworth, Chebyshev, and elliptic analog prototype filters is derived which generalizes the conventional biquadratic designs and provides flatter passbands and sharper band edges. The equalizer filter coefficients are computable in terms of the center frequency, peak gain, bandwidth, and bandwidth gain. The issues of filter order and bandwidth selection are considered, and the frequency-shifted transposed, normalized-lattice, and minimum roundoff-noise state-space realization structures are discussed. The design equations apply equally well to low-pass and high-pass shelving filters, and to ordinary bandpass and bandstop filters.
Authors: Avis, Mark R.; Xiao, Lejun; Cox, Trevor J.
In comparison to active absorbers, active diffusers have more complicated target impedance functions, a smaller region of stable control, and are more sensitive to control impedance errors. The issues of stability and sensitivity are analyzed theoretically and empirically. Measurements show comparable performance for active and passive diffusers with the active solution requiring less space.
Authors: Bai, Mingsian R.; Liao, Jerwoei
[Engineering Reports] Miniature loudspeakers are key components of mobile phones in modern-day wireless communication. Although the fundamental principle of miniature loudspeakers is similar to that of larger loudspeakers of other kinds, there are still some distinct features of these devices that may give rise to different design considerations. An extensive electroacoustic analysis is conducted to explore the characteristics of miniature loudspeakers when fitted to the interior of mobile phones. Of particular interest is the modeling of the duct structure in the analysis. Thiele and Small parameters of miniature loudspeakers are experimentally identified. Dynamic response simulation is carried out on the basis of electro-mechano-acoustical (EMA) equivalent circuits. Head diffraction in hands-free application is also simulated. In order to assess the miniature loudspeakers, performance indices including frequency response, sensitivity, and efficiency are measured. An acoustic design that extends the low-frequency bandwidth is also presented to meet the ever-increasing demand of sound quality of miniature loudspeakers.
Authors: Staff, AES
[Feature Article] Loudspeakers have remained relatively unchanged in their basic design for many decades, but recent approaches have begun to take advantage of the characteristics of multidriver arrays. In this article we will review AES 118th Convention papers that describe novel developments involving loudspeaker arrays, including digital transducer arrays, multi-actuator panels, and parametric array loudspeakers. The conventional moving-coil cone driver has held sway in the loudspeaker market for many years, but there is strong research activity in new areas where, for example, miniaturization, spatial control, or direct digital conversion is envisaged.
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