AES New York 2015
Paper Session P9
P9 - Transducers—Part 3: Loudspeakers
Friday, October 30, 2:00 pm — 5:00 pm (Room 1A08)
Chair:
Peter John Chapman, Harman - Denmark; Bang & Olufsen Automotive
P9-1 A Model for the Impulse Response of Distributed-Mode Loudspeakers and Multi-Actuator Panels—David Anderson, University of Rochester - Rochester, NY, USA; Mark F. Bocko, University of Rochester - Rochester, NY, USA
Panels driven into transverse (bending) vibrations by one or more small force drivers are a promising alternative approach in loudspeaker design. A mechanical-acoustical model is presented here that enables computation of the acoustic transient response of such loudspeakers driven by any number of force transducers at arbitrary locations on the panel and at any measurement point in the acoustic radiation field. Computation of the on- and off-axis acoustic radiation from a panel confirms that the radiated sound is spatially diffuse. Unfortunately, this favorable feature of vibrating panel loudspeakers is accompanied by significant reverberant effects and such loudspeakers are poor at reproducing signals with rapid transients.
Convention Paper 9409 (Purchase now)
P9-2 Loudspeaker Rocking Modes (Part 1: Modeling)—William Cardenas, Klippel GmbH - Dresden, Germany; Wolfgang Klippel, Klippel GmbH - Dresden, Germany
The rocking of the loudspeaker diaphragm is a severe problem in headphones, micro-speakers, and other kinds of loudspeakers causing voice coil rubbing that limits the maximum acoustical output at low frequencies. The root causes of this problem are small irregularities in the circumferential distribution of the stiffness, mass, and magnetic field in the gap. A dynamic model describing the mechanism governing rocking modes is presented and a suitable structure for the separation and quantification of the three root causes exciting the rocking modes is developed. The model is validated experimentally for the three root causes and the responses are discussed conforming a basic diagnostics analysis.
Convention Paper 9410 (Purchase now)
P9-3 Active Transducer Protection Part 1: Mechanical Overload—Wolfgang Klippel, Klippel GmbH - Dresden, Germany
The generation of sufficient acoustical output by smaller audio systems requires maximum exploitation of the usable working range. Digital preprocessing of audio input signals can be used to prevent a mechanical or thermal overload generating excessive distortion and eventually damaging the transducer. The first part of two related papers focuses on the mechanical protection defining useful technical terms and the theoretical framework to compare existing algorithms and to develop meaningful specifications required for the adjustment of the protection system to the particular transducer. The new concept is illustrated with a micro-speaker and the data exchange and communication between transducer manufacturer, software provider, and system integrator are discussed.
Convention Paper 9411 (Purchase now)
P9-4 Horns Near Reflecting Boundaries—Bjørn Kolbrek, Norwegian University of Science and Technology - Trondheim, Norway
It is well known that when a sound source is placed near one or more walls, the power output increases due to the mutual coupling between the source and its image sources. This is reflected in an increase in the low frequency radiation resistance as seen by the sources. While direct radiating loudspeakers may benefit from this whenever the sources are within about a quarter wavelength of each other, horns will behave differently depending on if the increase in radiation resistance comes within the pass band of the horn or not. This has implications for the placement of corner horns. In this paper the Mode Matching Method (MMM) is used together with the modal mutual radiation impedance and the concept of image sources to compute the throat impedance and radiated sound pressure of horns placed near infinite, perpendicular reflecting boundaries. The MMM is compared with another numerical method, the Boundary Element Rayleigh Integral Method (BERIM), and with measurements and is shown to give good agreement with both. The MMM also has significantly shorter computation time than BERIM, making it attractive for use for the initial iterations of a design, or for optimization procedures.
Convention Paper 9412 (Purchase now)
P9-5 State-Space Modeling of Loudspeakers Using Fractional Derivatives—Alexander King, Technical University of Denmark - Kgs. Lyngby, Denmark; Finn T. Agerkvist, Technical University of Denmark - Kgs. Lyngby, Denmark
This work investigates the use of fractional order derivatives in modeling moving-coil loudspeakers. A fractional order state-space solution is developed, leading the way towards incorporating nonlinearities into a fractional order system. The method is used to calculate the response of a fractional harmonic oscillator, representing the mechanical part of a loudspeaker, showing the effect of the fractional derivative and its relationship to viscoelasticity. Finally, a loudspeaker model with a fractional order viscoelastic suspension and fractional order voice coil is fit to measurement data. It is shown that the identified parameters can be used in a linear fractional order state-space model to simulate the loudspeakers’ time domain response.
Convention Paper 9413 (Purchase now)
P9-6 Comparative Static and Dynamic FEA Analysis of Single and Dual Voice Coil Midrange Transducers—Felix Kochendörfer, JBL/Harman Professional - Northridge, CA USA; Alexander Voishvillo, JBL/Harman Professional - Northridge, CA, USA
The concept of the dual coil direct-radiating loudspeakers have been known for several decades. JBL Professional pioneered in design and application of dual coil woofers and midrange loudspeakers. There are several properties of the dual coil transducers that differentiate them from the traditional single voice coil design. First is the better heat dissipation—the dual coil may be considered as a traditional coil slit in two parts and each one is positioned into its own magnetic gap. Second is the symmetry of the force factor (Bl product) versus position of the voice coils in their gaps. It is explained by the fact that one coil leaves its gap the other one on contrary enters its gap. These two features are well researched and described in literature [1,2]. Less is known about advantage of the dual coil transducers related to the flux modulation and dependence of the alternating magnetic flux (and corresponding voice coil inductance) on frequency, current, and voice coil positions. In this work comparison of a regular single coil design and dual coil configuration is carried out through dynamic magnetic FEA modeling and measurements.
Convention Paper 9414 (Purchase now)
