Transducers Part 2

Paper Sessions

P06-1 On the Interdependence of Loudspeaker Motor Nonlinearities—Finn T. Agerkvist, Technical University of Denmark - Kgs. Lyngby, Denmark; Franz Heuchel, Technical University of Denmark - Kgs. Lyngby, Denmark
Two of the main nonlinearities in the electrodynamic loudspeaker are the position dependence of the force factor, Bl, and the voice coil inductance, Le. Since they both are determined by the geometry of the motor structure, they cannot be independent. This paper investigates this dependence both analytically and via FEM simulations. Under certain simplifying assumptions the force factor can be shown to be proportional to the spatial derivative of the inductance. Using FEM simulations the implications of this relation is illustrated for drivers with more realistic geometry and material parameters. 

P06-2 Comparison of Dynamic Driver Current Feedback Methods—Juha Backman, Huawei Technologies - Tampere, Finland; Genelec Oy - Iisalmi, Finland
Current feedback is a versatile method of modifying the behavior of a loudspeaker driver, with opportunity for linearization and matching the driver to the enclosure design targets, but depending on the chosen approach a potential risk of increasing the effects of either voice coil impedance variation or driver mechanical parameter nonlinearity. This work compares using a nonlinear simulation model various forms of current feedback, including current drive, finite positive or negative amplifier resistances, and negative resistance combined with a reactance. 

P06-3 Non-Linear Optimization of Sound Field Control at Low Frequencies Produced by Loudspeakers in Rooms—Adrian Celestinos, Samsung Research America - Valencia, CA, USA; Pascal Brunet, Samsung Research America - Valencia, CA USA; Audio Group - Digital Media Solutions; Glenn S Kubota, Samsung Research America - Valencia, CA, USA
The low-frequency response of loudspeakers can be affected severely when placed in typical living rooms. Past investigations have focused on reducing the energy at the room resonances but not reducing seat-to-seat variation. Other works, using multiple loudspeakers, nullify the room modes or eliminate them with acoustic interference but are restricted by loudspeaker position and room geometry. In this work the loudspeaker position is not restricted and both frequency and time-domain methods are explored. Nonlinear optimization has been computed to improve the time response of the speaker in the room. Results have shown significant reduction of seat-to-seat variation. The time-frequency analysis reveals elimination of room resonances; producing a clear tight bass response. 

P06-4 Evaluation of Efficiency and Voltage Sensitivity in Horn Drivers—Alexander Voishvillo, JBL/Harman Professional Solutions - Northridge, CA, USA; Brian McLaughlin, Harman Professional - Northridge, CA, USA
There is a belief in horn driver design that if the resistive component of the input impedance of the diaphragm’s acoustical load is equal to the DC component of the voice coil’s electrical impedance, a maximum efficiency of 50% can be reached. This work shows that in reality, the compression driver’s real efficiency differs from the classical theory prediction. The discrepancy is explained by the fact that the driver’s output impedance and the acoustical loading impedance are different functions, not mere resistances. Additionally, the input electrical power and the output acoustical power are essentially integral functions of frequency and can be expressed by single numbers rather than frequency-dependent functions. Examples illustrating dependence of efficiency and sensitivity on various parameters are given. 

P06-5 Characterization of Nonlinear Port Parameters in Loudspeaker Modeling—Doug Button, Harman International - Northridge, CA, USA; Russ Lambert, L3 Communications - Salt Lake City, UT, USA; Pascal Brunet, Samsung Research America - Valencia, CA USA; Audio Group - Digital Media Solutions; James Bunning, Harman International - Northridge, CA, USA
The outputs from ports used in common vented box loudspeakers are not linear with input level. With the goal of developing accurate modeling of vented boxes, a new method for estimation of nonlinear port parameters is shown. Acoustic mass and acoustic resistance parameters change with pressure in the enclosure and velocity in the port. Along with all nonlinear speaker parameters required for modeling, a practical way to characterize the changing acoustic mass and acoustic resistance is presented and tested with measurements. Using the new method, nonlinear port parameters are extracted for multiple box and port types.