AES New York 2009
Paper Session P4

P4 - Transducer Modeling and Design

Friday, October 9, 2:30 pm — 7:00 pm
Chair: Siegfried Linkwitz

P4-1 Modeling the Intermodulation Distortion of a Coaxial Loudspeaker—Edward Dupont, Stanley Lipshitz, University of Waterloo - Waterloo, Ontario, Canada
This paper is an attempt to explain the intermodulation distortion of a coaxial loudspeaker driver. Such a loudspeaker, in which the woofer and tweeter are excited at frequencies f₁ and f₂ respectively, is known to produce sum and difference frequencies f± = f₁ ± f₂. Generation of these can be attributed to both the nonlinearity of the equations of motion and the Lagrangian boundary behavior of the woofer. A simplified model is used consisting of an acoustic monopole located in front of a baffled planar piston. To characterize the phenomena of interest the second-order equation for pressure is used. An exact integral solution is then given for the f± pressure terms. A special case analytic solution is also discussed. Several numerical investigations of the model are performed and compared with experiment.
Convention Paper 7840 (Purchase now)

P4-2 Study and Characterization of the Odd and Even Nonlinearities in Electrodynamic Loudspeakers by Periodic Random-Phase Multisines—Pepe Gil-Cacho, Toon van Waterschoot, Marc Moonen, Katholieke Universiteit Leuven (KUL) - Leuven, Belgium; Søren Holdt Jensen, Aalborg University - Aalborg, Denmark
In acoustic echo cancellation (AEC) applications, often times an acoustic path from a loudspeaker to a microphone is estimated by means of a linear adaptive filter. However, loudspeakers introduce nonlinear distortions that may strongly degrade the adaptive filter performance, thus nonlinear filters have to be considered. In this paper measurements of three types of loudspeakers are conducted to detect, quantify, and qualify nonlinearities by means of periodic random-phase multisines. It is shown that odd nonlinearities are more predominant than even nonlinearities over the entire frequency range. The aim of this paper is then to demonstrate that third-order (cubic) adaptive filters have to be used, which is in clear conflict with the extensive, almost unique, use of second-order (quadratic) Volterra filters.
Convention Paper 7841 (Purchase now)

P4-3 The Effect of Sample Variation among Cabinets of a Line Array on Simulation Accuracy—Stefan Feistel, Wolfgang Ahnert, Ahnert Feistel Media Group - Berlin, Germany
Most line array systems consist of a number of discrete sound sources. For typical performance criteria of such arrays, such as the homogeneous, controlled radiation of sound or its minimum variation among mechanically identical arrays, it is important that the radiation properties such as sensitivity and directional response of the individual sources are very similar. Based on statistical means, we discuss the effect of sample variation on the overall array performance. We show that for typical modeling applications the influence of sample variation is small and that it can be neglected in most cases as a minor error. Our results are derived by three different methods, a rigorous mathematical analysis, numerical simulations, and exemplary measurements.
Convention Paper 7842 (Purchase now)

P4-4 SPICE Simulation of Headphones and Earphones—Mark Kahrs, University of Edinburgh - Edinburgh, UK
Unlike loudspeakers, headphones and earphones are not in the mainstream of electroacoustical design. In this paper different designs for headphones and earphones are discussed and simulated with the aid of SPICE, the well-known electrical circuit simulator. These simulations can be used to perform elementary design tradeoffs. One significant difficulty is the lack of component measurements in the open literature. The paper begins with an overview of design aspects of headphones. This is followed by a review of the use of SPICE as an electroacoustical simulator. The following section details various experiments done using SPICE to explore headphone design. The conclusion decries the lack of publicly available information as well as the dearth of components.
Convention Paper 7843 (Purchase now)

P4-5 A Preliminary SPICE Model to Calculate the Radiation Impedance of a Baffled Circular Piston—Scott Porter, Stephen Thompson, The Pennsylvania State University - State College PA, USA
Acoustic systems often use circular pistons to radiate sound into fluid media. Mathematically, the solution to the radiation impedance of a baffled circular piston is well known. Implementing the exact solution in circuit analysis packages, such as SPICE, however, can be difficult because many commercial packages do not include Bessel and Struve functions. A SPICE subcircuit is presented that calculates the radiation impedance for all frequencies to a good approximation.
Convention Paper 7844 (Purchase now)

P4-6 Comparison between Measurement and Boundary Element Modelization of Subwoofers—Manuel Melon, Christophe Langrenne, Olivier Thomas, Alexandre Garcia, CNAM - Paris, France
At very low frequency, even large anechoic chambers cannot be used to measure subwoofers accurately. A solution consists in using the Field Separation Method (FSM). This technique allows subtracting the field reflected by the measurement room walls to the measured field, thus recovering the acoustic pressure that would have been radiated under free field conditions. In this paper Field Separation Method is used to measure two subwoofer prototypes. Results are compared to the ones given by a boundary element modelization of the subwoofers. Input velocities required for the modeling are measured by using a laser Doppler vibrometer. Comparisons are performed on the following quantities: on-axis pressure and directivity. Discrepancies between results obtained by these two methods are discussed and explained when possible.
Convention Paper 7845 (Purchase now)

P4-7 Design of a Coincident Source Driver Array with a Radial Channel Phase-Plug and Novel Rigid Body Diaphragms—Mark Dodd, GPAcoustics (UK) Ltd. - Maidstone, Kent, UK; Jack Oclee-Brown, KEF Audio (UK) Ltd. - Maidstone, Kent, UK
The simple source characteristics that coincident-source driver arrays promise are an attractive design goal, but many engineering obstacles must be overcome to avoid undesirable complex behavior. This paper outlines an innovative design approach that achieves simple source behavior over several octaves and avoids the complex acoustical and vibrational behavior found in traditional drivers. The high frequency section of the driver combines techniques for optimizing the response introduced by Dodd and the radial channel phase-plug design, introduced by the authors. The midrange unit uses a cone with novel geometry allowing it to move as a rigid body to cover an octave above the crossover frequency. The resulting driver and its measured behavior is described in the light of some possible alternative approaches.
Convention Paper 7846 (Purchase now)

P4-8 New Induction Drive Transducer Designs—Marshall Buck, Psychotechnology, Inc. - Los Angeles, CA, USA; Patrick Turnmire, RedRock Acoustics - Arroyo Seco, NM, USA; David Graebener, Wisdom Audio, LLC - Carson City, NV, USA
Induction motor designs for a loudspeaker typically use a transformer assembly with a fixed primary and moving secondary (driving ring) immersed in a static magnetic field. Induction drive audio transducers can be designed to produce very high efficiency, high output mid/high devices. In another configuration a very linear, long stroke woofer with high output is realizable. Measurements will be provided on prototypes of both types of devices. The midrange exhibits an output of 83 acoustic watts with 300 Watts drive, and a maximum 10 Watt efficiency of 45%. The devices have a very linear stroke with both Bl vs. X and Le vs. X extremely flat. Reliability is enhanced over conventional voice coil drive means due to the elimination of moving lead in wires. A wide range of nominal impedances can be designed by changing the wire size and number of turns in the primary.
Convention Paper 7847 (Purchase now)

P4-9 A Thin and Flexible Sound Generator Using an Electro-Active Elastomer—Takehiro Sugimoto, Kazuho Ono, Akio Ando, NHK Science & Technology Research Laboratories - Setagaya-ku, Tokyo, Japan; Yuichi Morita, Kosuke Hosoda, Daisaku Ishii, Foster Electric Co., Ltd. - Akishima, Tokyo, Japan
We propose a new sound generator using electroactive elastomer (EAE), which is an elastic and flexible material. Our prototype sound generator is composed of a thin polyurethane elastomer sheet and conducting polymer electrodes. The electrodes are formed on both surfaces of the elastomer sheet and are driven by audio signals with a DC bias voltage. We conducted a transformation analysis of the EAE and found that using of the side-length change is more effective than using the thickness change. An EAE sound generator provides 30 dB higher sound pressure level (SPL) at 1 kHz than one using thickness change. The configuration design and operating conditions suitable for a sound generator are discussed.
Convention Paper 7848 (Purchase now)