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v3.0, 20040325, ME

Session Z9 Tuesday, May 11 09:30 h–11:00 h
Posters: Loudspeakers & Microphones

Frequency Domain Experiences in Loudspeaker’s SuspensionsFernando Bolaños, Acústica Beyma S.A., Valencia, Spain
This paper proposes to individually analyze each component of a loudspeaker, specifically the diaphragm-surround set. Experiments were performed on low- and medium-amplitude displacement ranges. The paper uses traditional experimental methods in seeking the surround and diaphragm’s spectral signatures in the main eigen-value region. Our method consisted in exciting the diaphragm-surround set by a reluctance transducer that was fed by an electric impulse. We then analyzed its response with an Eddy Current Displacement Transducer in the Frequency Domain. The most typical experimental spectral signatures of the nonlinear systems in free response were reviewed. This paper presents the results that were obtained after examining six samples, finding only one sample completely free of nonlinearities.
Z9-2 Nonuniform Voice-Coil Winding for Electrodynamic LoudspeakerVictor Mazin, Yong-Sang Lee, Samsung BlueTek co. Ltd., Suwon City, Korea
In electrodynamic loudspeakers the force factor Bl is an irregular and asymmetrical function of voice-coil displacement. This results in diverse distortion during voice-coil oscillation. In this paper a method of artifact reduction is suggested. This method is based on application of nonuniform voice-coil winding, i.e., number of layers varies along the vice-coil axis. The voice coil proposed allows a more regular and symmetrical B1 factor than a conventional voice coil. Theoretical background of the method is given. Effects of the nonuniform voice coil on loudspeaker performance have been investigated using the Klippel Distortion Analyzer.
Z9-3 An Active Biquadratic Filter for Equalizing Overdamped LoudspeakersNeville Thiele, Consultant, Epping, New South Wales, Australia
When a bridged-T network is inserted into the feedback path of a voltage follower, it can produce an inexpensive biquadratic filter whose transfer function has first-order coefficients as low as 2.5 (Q = 0.4), often approaching 2 (Q = 0.5), in the numerator when those in the denominator lie in the very useful range between 0.5 and 2. Among its applications, it is peculiarly suited to equalizing “over-damped” loudspeakers, i.e., with exceptionally low QT’s, that are typical of robust, sensitive drivers with large magnets. The wide range of applications is possible through selection of the more suitable of the two possible configurations of a bridged-T network described as CRRC or RCCR. The work is the subject of intellectual property claims.
Z9-4 Radiation of an Enclosed Loudspeaker in a Large Baffle: Loudspeaker Simulation ModelElena Prokofieva, Linn Products Ltd., Glasgow, Scotland, UK
A theoretical step-by-step investigation of the conventional loudspeaker, placed into a sealed cabinet and then installed within a rigid wall has been conducted. The loudspeaker diaphragm was simulated by a rigid circle piston and then by a number of concentric rings inserted into a large but finite-sized baffle and enclosure. The acoustic pressure and dynamic displacement expressions were formulated using a quasi-dynamic approach to loading force representation. This simulation allows for the withdrawal of some standard assumptions commonly used in the traditional theory of plates. A block-scheme of a proposed computer simulation using the developed quasi-dynamic model is also presented.
Z9-5 Practical Considerations for Integrating Switch Mode Audio Amplifiers and Loudspeakers for a Higher Power EfficiencySøren Poulsen, Michael A. E. Andersen, Technical University of Denmark, Lingby, Denmark
An integration of electrodynamic loudspeakers and switch mode amplifiers has earlier been proposed in Karsten Nielsen, Lars Michael Fenger, “The Active Pulse Modulated Transducer (AT), A Novel Audio Power Conversion System Architecture,” AES 115th Convention Paper, October 2003. The work presented in this paper is related to the practical aspects of integration of switch mode audio amplifiers and electro dynamic loudspeakers, using the speaker’s voice coil as output filter, and the magnetic structure as heat sink for the amplifier.
Z9-6 Sound Radiation from a Dual Microflim Piezoelectric Loudspeaker in Free SpaceTim Mellow, Nokia Product Technology Platforms, Farnborough, UK
Radiation characteristics of a concept loudspeaker are calculated. It comprises two closely-spaced stretched piezoelectric membranes pushed apart by a pressurized gas. A drive voltage applied across conductive coatings on both membranes causes their tensions to vary in opposite phase. Consequently, the membranes are displaced in the same direction. Driven by a class D amplifier, this transducer offers higher efficiency than conventional moving coil technology but with the smooth response and light weight of electrostatic devices. However, the voltage requirement is lower and the potential SPL higher than the latter. Also, if the conductive coatings were transparent, there is the tantalizing possibility of combining it with a display. The only remaining question is whether it can be manufactured economically.
Z9-7 Sound Source Design in the Very Low-Frequency Domain— Guillaume Pellerin, Jean-Dominique Polack, Jean-Pierre Morkerken, Laboratoire d’Acoustique Musicale, Paris, France
Whereas the aerodynamic effects take a significant place in the behavior of sound sources in the low-frequency domain and for signals containing a high specific energy, new complex fluid parameters have to be implemented to take into account possible causes of sound distortion such as the stalling phenomenon in the boundary layer around the mechanical structure. For the design of vented boxes, we show that the choice of a nozzle profile for the resonator ensures a better dynamical stability of the airflow and thus authorizes extreme low cutoff frequencies in “dipole” configurations. We also describe some experimental and computed results based on fluid FEM about the radiating output for this kind of source under 40 Hz.

Microphone Response in a Closed-Loop SystemMichael Pincus, Acentech, Inc., Cambridge, MA, USA
A closed-loop audio system can be defined as one in which the loudspeaker is in the same space as the microphone. As such, some sound from the loudspeaker will mix with the source creating an interference pattern. The interference is dependent on the path length from the loudspeaker back to the microphone, the amplitude of the interfering signal, and the latency of the forward-fed signal. This paper investigates this interference and its effect on the output response of the microphone.
Z9-9 Space Characteristics of Directed Single Gradient MicrophonesEmil Milanov, Elena Milanova, NEC, Sophia, Bulgaria
In this paper we examine a single gradient microphone with two acoustical entrances. A formula is proposed for defining the space characteristics of the microphone in its whole sound frequency range. The defined formulas are valid when the microphone is in a sphere sound wave and in a plane sound wave. We also explain the reasons that lead to the change of the space and frequency characteristics in the area of the high frequencies when no diffraction events are present.
Z9-10 Performance Study of a Compact 2-Sensor Noise Canceling System—Kok Soon Phua, Jian Feng Chen, Louis Shue, Han Wu Sun, Institute for InfoComm Research, Singapore
In this paper we propose a compact directional noise-canceling device, which consists of a differential microphone formed by two omnidirectional microphones connected in an end-fire orientation. By making use of adaptive beamforming for improved directionality, and spectral shaping, a form of nonlinear speech enhancement, the proposed device is positioned to tackle noise found in real environments, which is typically a mixture of directional, stationary, and nonstationary interferences. Performance evaluation of our real-time implementation is based on the following criteria: (1) directionality, (2) distortions, and (3) speech quality as measured by the Mean-Opinion-Score (MOS), through subjective listening tests and using the ITU-T P.862 Perceptual Evaluation of Speech Quality tool. Our experimental results indicate an average interference suppression of as much as 22 dB, and consistent improvement in speech quality.

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