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Last Updated: 20060906, mei

P10 - Loudspeakers - Part 2

Friday, October 6, 2:00 pm — 4:30 pm

Chair: Richard Little, Tymphany - Cupertino, CA, USA

P10-1 Loudspeaker-Room Adaptation for a Specific Listening Position Using Information about the Complete Sound FieldJan Abildgaard Pedersen, Lyngdorf Audio - Skive, Denmark
A novel method is presented for equalizing a loudspeaker for a specific listening position in order to compensate for an influence of the room in which it is positioned. The method is based on measuring the sound pressure in the listening position (focus position) and in at least three randomly selected positions scattered across the entire listening room (room positions). The measurement in the listening position holds information about the listener’s access to the sound field while the room positions hold information about the energy in the 3-D sound field. The correction for the listening position is then bound by upper and lower gain limits calculated as a function of frequency from the information about the 3-D sound field.
Convention Paper 6908 (Purchase now)

P10-2 Allpass Arrays: Theory, Design, and ApplicationsMichael Goodwin, Creative Advanced Technology Center - Scotts Valley, CA, USA
The realization of nondirectional linear electroacoustic arrays using Bessel weighting and other methods has been described in the literature. In this paper we discuss generalized allpass arrays; since the far-field response of a uniformly spaced linear array is specified by a mapping of the DTFT of the array weights, any FIR approximation of an allpass filter gives weights that result in a nearly uniform array response. We explain the fundamental array theory and present a straightforward method for the design of arbitrary-order allpass arrays. We further discuss applications of allpass arrays in crossover-filtered configurations and in the implementation of efficient frequency-invariant beamformers.
Convention Paper 6909 (Purchase now)

P10-3 Assessment of Nonlinearity in Transducers and Sound Systems —From THD to Perceptual ModelsAlex Voishvillo, JBL Professional - Northridge, CA, USA
Research of audibility of loudspeaker nonlinear distortion has not shown good correlation between traditionally used metrics (harmonics and intermodulation) and subjective performance. The problem of sound fidelity-related methods to assess nonlinearity in transducers has not been solved. Wide application of low-bit rate compression systems (MP3, etc.) demanded the development of objective measurement methods based on perceptual models. These methods, however, have not been used for measurement of loudspeakers, and they may not be optimal for that due to the different nature of the nonlinearity in transducers. Recently, perceptual models created specifically for the assessment of nonlinearity in transducers have emerged. In this paper analysis of the old and new methods, their comparison, and the prospects for future developments are discussed.
Convention Paper 6910 (Purchase now)

P10-4 An Important Aspect of Underhung Voice-Coils: A Technical Tribute to Ray NewmanRaymond J. Newman (Deceased), Electro-Voice Inc. - Buchanan, MI, USA; D. B. (Don) Keele, Jr., Harman International Industries, Inc. - Martinsville, IN, USA; David Carlson, Jim Long, Electro-Voice Div. Telex Communications - Burnsville, MN, USA; Kent Frye, Gentex Corporation - Zeeland, MI, USA; Matthew Ruhlen, John Sheerin, Harman/Becker Automotive Systems - Martinsville, IN, USA
In the1970s, Ray Newman while at Electro-Voice, single handedly and very successfully promoted the use of the then new concept of the Thiele/Small parameters and related design techniques for categorizing loudspeakers and systems to the loudspeaker industry. This paper posthumously recounts the contents of three significant Electro-Voice memos written in 1992 by Ray Newman concerning a comparison of overhung versus underhung loudspeaker motor assemblies. The information in the memos is still very relevant today. He proposed a comparison between the two assembly types assuming motors that had: (1) the same Xmax, (2) the same efficiency, (3) similar thermal behavior, and (4) the same voice coil. He calculated the required magnetic gap energy and discovered to his surprise that the magnet requirements actually went down dramatically when switching from an overhung to an underhung structure and depended only on the ratio between Xmax and the voice-coil length. This is in contrast with “common sense” that dictates that longer gaps mean larger magnets. He showed that for high-excursion motors, a switch could be made from a ferrite overhung structure to an equivalent high-energy neodymium underhung structure with little cost penalty. This paper recounts this early work and then presents motor predictions using a present-day magnetic FEM simulator. The results show that indeed, the magnetic energy required by an underhung motor is actually less than an overhung motor as long as the operating flux in the overhung motor’s core is below the point where the core and fringe losses are comparable to its gap energy. Ray’s original memos and notes will also be included as an appendix to the paper along with reminiscences from the paper’s co-authors.
Convention Paper 6911 (Purchase now)

P10-5 The Acoustic Center: A New Concept for Loudspeakers at Low FrequenciesJohn Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada
This paper focuses on the acoustic center, which represents a particular point for a normal sealed-box loudspeaker that acts as the origin of its low-frequency radiation. At low frequencies, the radiation from such a loudspeaker becomes simpler as the wavelength of the sound becomes large relative to the enclosure dimensions, and the system behaves externally as a spherical point source. Although there are near-field effects very close to the loudspeaker, the acoustic center has a clear meaning even a short distance from the enclosure, up to frequencies of about 200 Hz for typical systems. The low-frequency response of loudspeakers in rooms is determined by the position of their acoustic centers. The study is underpinned by: (1) a mathematical multipole expansion of the output of a loudspeaker, (2) an acoustic boundary-element calculation of a number of loudspeaker systems, (3) some measurements that corroborate the concept of the acoustic center, and (4) a discussion of a number of relevant concepts.
Convention Paper 6912 (Purchase now)

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