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AES Munich 2009
Paper Session P5

P5 - Loudspeakers

Thursday, May 7, 14:00 — 18:00
Chair: John Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada

P5-1 Estimating the Velocity Profile and Acoustical Quantities of a Harmonically Vibrating Loudspeaker Membrane from On-Axis Pressure DataRonald M. Aarts, Philips Research Europe - Eindhoven, The Netherlands, Technical University of Eindhoven, Eindhoven, The Netherlands; Augustus J. Janssen, Philips Research Europe - Eindhoven, The Netherlands
Formulas are presented for acoustical quantities of a harmonically excited resilient, flat, circular loudspeaker in an infinite baffle. These quantities are the sound pressure on-axis, far-field, directivity and the total radiated power. These quantities are obtained by expanding the velocity distribution in terms of orthogonal polynomials. For rigid and non-rigid radiators, this yields explicit, series expressions for both the on-axis and far-field pressure. In the reverse direction, a method of estimating velocity distributions from (measured) on-axis pressures by matching in terms of expansion coefficients is described. Together with the forward far-field computation scheme, this yields a method for assessment of loudspeakers in the far-field and of the total radiated power from (relatively near-field) on-axis data (generalized Keele scheme).
Convention Paper 7678 (Purchase now)

P5-2 Testing and Simulation of a Thermoacoustic Transducer PrototypeFotios Kontomichos, Alexandros Koutsioubas, John Mourjopoulos, Nikolaos Spiliopoulos, Alexandros Vradis, Stamatis Vassilantonopoulos, University of Patras - Patras, Greece
Thermoacoustic transduction is the transformation of thermal energy fluctuations into sound. Devices fabricated by appropriate materials utilize such a mechanism in order to achieve acoustic wave generation by direct application of an electrical audio signal and without the use of any moving components. A thermoacoustic transducer causes local vibration of air molecules resulting in a proportional pressure change. The present paper studies an implementation of this alternative audio transduction technique for a prototype developed on silicon wafer. Measurements of the performance of this hybrid solid state device are presented and compared to the theoretical principles of its operation, which are evaluated via simulations.
Convention Paper 7679 (Purchase now)

P5-3 Analysis of Viscoelasticity and Residual Strains in an Electrodynamic LoudspeakerIvan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia; Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia
An electrodynamic loudspeaker was analyzed in three steps: (a) as a device supplied by the market, (b) removed upper suspension, and (c) dismantled assembly consisting only of vibrating spider and voice coil. In three steps, resonant frequency and stiffness were measured dynamically for driving currents up to 100 mA, whereas stiffness was also measured quasi-statically by the use of calibrated masses. It was found that widely quoted effect of decreasing resonant frequency, as plotted against driving current, comes from the residual strain in the vibrating material, and significant contribution is associated with the spider. When driving current increases residual strain is gradually compensated, giving rise to the minimum of stiffness, and further increase of resonant frequency is attributed to a common nonlinearity in the forced vibrating system.
Convention Paper 7680 (Purchase now)

P5-4 Forces in Cylindrical Metalized Film Audio CapacitorsPhilip J. Duncan, University of Salford, Greater Manchester, UK; Nigel Williams, Paul S. Dodds, ICW Ltd. - Wrexham, Wales, UK
This paper is concerned with the analysis of forces acting in metalized polypropylene film capacitors in use in loudspeaker crossover circuits. Capacitors have been subjected to rapid discharge measurements to investigate mechanical resonance of the capacitor body and the electrical forces that drive the resonance. The force due to adjacent flat current sheets has been calculated in order that the magnitude of the electro-dynamic force due to the discharge current can be calculated and compared with the electrostatic force due to the potential difference between the capacitor plates. The electrostatic force is found to be dominant by several orders of magnitude, contrary to assumptions in previous work where the electro-dynamic force is assumed to be dominant. The capacitor is then modeled as a series of concentric cylindrical conductors and the distribution of forces within the body of the capacitor is considered. The primary outcome of this is that the electrostatic forces act predominantly within the inner and outer turn of the capacitor body, while all of the forces acting within the body of the capacitor are balanced almost to zero. Experimental results where resonant acoustic emissions have been measured and analyzed are presented and discussed in the context of the model proposed.
Convention Paper 7682 (Purchase now)

P5-5 On the Use of Motion Feedback as Used in 4th Order SystemsStefan Willems, Denon & Marantz Holding, Premium Sound Solutions - Leuven Belgium; Guido D’Hoogh, Retired
Class D amplification allows the design of compact very high power amplifiers with a high efficiency. Those amplifiers are an excellent candidate for being used in compact high-powered subwoofers. The drawback of compact subwoofers is the nonlinear compression of the air inside the (acoustically) small box. Fourth order systems are beneficial over 2nd order systems due to their increased efficiency. To combine the best of both worlds, 4th order design and acoustically small enclosures, a feedback mechanism has been developed to reduce the nonlinear distortion found in compact high-powered subwoofers. Acceleration feedback on woofer systems is traditionally used in 2nd order systems. This paper discusses the use of an acceleration and velocity feedback system applied to a 4th order system.
Convention Paper 7683 (Purchase now)

P5-6 Mapping of the Loudspeaker Emission by the Use of Anemometric MethodDanijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia; Ivan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia
Lateral wire anemometry (LWA) has been developed for recording of air vibration. Standard anemometry is founded upon the hot wire method, and wire temperature changes in the oscillating air velocity in the range 800-1000 °C, which is less suitable because of the proper heat emission from the wire. LWA deals only with the initial slope of the changing wire resistance, and subsequent Fourier analysis enables measurements of periodic air velocity. The probe has been developed for precise mapping of the air velocity field in the front of the membrane, and local power emission of the membrane may be evaluated in the region fitted to 0.15 cm2.
Convention Paper 7684 (Purchase now)

P5-7 Flat Panel Loudspeaker Consisting of an Array of Miniature TransducersDaniel Beer, Stephan Mauer, Sandra Brix, Fraunhofer Institute for Digital Media Technology IDMT - Ilmenau, Germany; Jürgen Peissig, Sennheiser Electronic GmbH & Co. KG - Wedemark, Germany
Multichannel audio reproduction systems like the Wave Field Synthesis (WFS) use a large number of small and closely spaced loudspeakers. The successful use of WFS requires, among other things, the ability of an "invisible” integration of loudspeakers in a room. Flat panel loudspeakers compared with conventional cone loudspeakers provide advantages in the space saved room integration because of their low manufactured depth. In this way flat panel loudspeakers can be found in furniture, media devices, or like pictures hung on the wall. Besides the integration, flat loudspeakers should provide at least the same good acoustical performance as conventional loudspeakers. This is indeed a problem, because the low depth negatively influences the acoustical quality of reproduction in the lower and middle frequency range. This paper demonstrates a new flat panel loudspeaker consisting of an array of miniature transducers.
Convention Paper 7685 (Purchase now)

P5-8 Subwoofer Loudspeaker System with Dynamic Push-Pull DriveDrazenko Sukalo, DSLab–Device Solution Laboratory - Munich, Germany
This paper examines the influence of mutual coupling between two driver-diaphragms driven by two electrical signals, each with a 90° phase shift on the voice-coil impedance curve. A new model of the system is described, and the effects are observed using the electrical circuit simulator PSpice. Finally, predicted and measured values are presented.
Convention Paper 7686 (Purchase now)