Transducers—Part 3

Friday, October 20, 9:00 am — 11:30 am (Rm 1E11)

Chair:
Scott Norcross, Dolby Laboratories - San Francisco, CA, USA

P12-1 Objective Testing of High-End Audio Systems—Gregor Schmidle, NTi Audio AG - Schaan, Liechtenstein; Gerd Köck, Art Déco Acoustics by Audio Manufaktur Köck - Kornwestheim, Germany; Brian MacMillan, NTi Audio Inc. - Portland, OR, USA
The high-end audio equipment market is filled with extraordinary products. Although the engineering and the materials utilized are often of the finest available, the quality control of such systems is frequently done subjectively rather than objectively. This paper shows some best practice examples of how to deploy effective quality measurement systems through the complete life cycle (R&D, QC installation, and repair) of high-end audio systems. 

P12-2 Theory of Constant Directivity Circular-Arc Line Arrays—Richard Taylor, Thompson Rivers University - Kamloops, BC, Canada; D. B. (Don) Keele, Jr., DBK Associates and Labs - Bloomington, IN, USA
We develop the theory for a broadband constant-beamwidth transducer (CBT) formed by a continuous circular-arc isophase line source. Appropriate amplitude shading of the source distribution leads to a far-field radiation pattern that is constant above a cutoff frequency determined by the prescribed beam width and arc radius. We derive two shading functions, with cosine and Chebyshev polynomial forms, optimized to minimize this cutoff frequency and thereby extend constant-beamwidth behavior over the widest possible band. We illustrate the theory with simulations of magnitude responses, full-sphere radiation patterns and directivity index, for example designs with both wide- and narrow-beam radiation patterns. 

P12-3 Constant Directivity Circular-Arc Arrays of Dipole Elements—Richard Taylor, Thompson Rivers University - Kamloops, BC, Canada; Kurtis Manke, Thompson Rivers University - Kamloops, BC, Canada; D. B. (Don) Keele, Jr., DBK Associates and Labs - Bloomington, IN, USA
We develop the theory for a broadband constant-beamwidth transducer (CBT) formed by a conformal circular-arc line array of dipole elements. Just as for CBT arrays of point sources, with suitable amplitude shading of the source distribution the far-field radiation pattern is constant above a cutoff frequency. This cutoff frequency is determined by the prescribed beam width and arc radius. We illustrate the theory with examples, including numerical simulations of magnitude responses, full-sphere radiation patterns, and directivity index. Unlike a circular-arc array of monopole elements, a dipole CBT maintains directivity control at low frequency. We give an example of one such array that achieves just 1 dB variation in directivity index over all frequencies. 

P12-4 Voice Coil Temperature—Non Linearity Compensations for Ultra Audio Band Impedance Probing—Isao Anazawa, Ny Works - Toronto, ON, Canada
As loudspeaker output power of mobile devices increases for better audio experience, an accurate measurement or estimation of the voice coil temperature becomes necessary in order to protect the loudspeaker from over-heating. A voice coil designed with a short ring, a metal pole piece, or under hung voice coil will most likely exhibit impedance nonlinearity. A voice coil resistance based temperature measurement method that relies on the resistance value may be adversely affected by voice coil impedance nonlinearity when the resistance is measured using high frequency probing. For this reason, the nonlinearity must be known and compensated. This paper analyzes and explains voice coil high frequency impedance characteristics due to Eddy losses and impedance nonlinearity, and develops a method to compensate voice coil impedance nonlinearity to obtain an accurate voice coil temperature measurement. 

P12-5 Variable Fractional Order Analysis of Loudspeaker Transducers: Theory, Simulations, Measurements, and Synthesis—Andri Bezzola, Samsung Research America - Valencia, CA USA; Pascal Brunet, Samsung Research America - Valencia, CA USA; Audio Group - Digital Media Solutions; Shenli Yuan, Center for Computer Research in Music and Acoustics (CCRMA), Stanford University - Stanford, CA, USA
Loudspeaker transducer models with fractional derivatives can accurately approximate the inductive part of the voice coil impedance of a transducer over a wide frequency band, while maintaining the number of fitting parameters to a minimum. Analytical solutions to Maxwell equations in infinite lossy coils can also be interpreted as fractional derivative models. However, they suggest that the fractional order a  cannot be a constant, but rather a function of frequency that takes on values between 1/2 and 1. This paper uses Finite Element (FEM) simulations to bridge the gap between the theoretical first-principles approach and lumped parameter models using fractional derivatives. The study explores the dependence of a on frequency for idealized infinite and finite cores as well as in four real loudspeaker transducers. To better match the measured impedances and frequency-dependent a values we propose to represent the voice coil impedance by a cascade of R-L sections.