AES London 2010
Paper Session P15

P15 - Loudspeakers and Headphones: Part 2

Monday, May 24, 09:00 — 12:00 (Room C5)
Chair: John Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada

P15-1 Chameleon Subwoofer Arrays—Generalized Theory of Vectored Sources in a Closed Acoustic Space—Adam J. Hill, Malcolm O. J. Hawksford, University of Essex - Colchester, UK
An equalization model is presented that seeks optimal solutions to wide area low-frequency sound reproduction in closed acoustic spaces. The methodology improves upon conventional wisdom by incorporating a generalized subwoofer array where individual frequency dependent loudspeaker polar responses are described by complex spherical harmonic frequency dependent functions. Multi-point system identification is performed using three-dimensional finite-difference time-domain simulation with optimization applied to seek global equalization represented by a set of orthogonal transfer functions applied to each spherical harmonic of each subwoofer within the array. The system is evaluated within a three-dimensional virtual acoustic space using both time and frequency domain metrics.
Convention Paper 8074 (Purchase now)

P15-2 Dynamical Measurement of the Effective Radiation Area S_D—Wolfgang Klippel, University of Dresden - Dresden, Germany; Joachim Schlechter, Klippel GmbH - Dresden, Germany
The effective radiation area S_D is one of the most important loudspeaker parameters because it determines the acoustical output (SPL, sound power) and efficiency of the transducer. This parameter is usually derived from the geometrical size of the radiator considering the diameter of half the surround area. This conventional technique fails for microspeakers and headphone transducers where the surround geometry is more complicated and the excursion varies not linearly versus radius. The paper discusses new methods for measuring the S_D more precisely. The first method uses a laser sensor and microphone to measure the voice coil displacement and the sound pressure generated by the transducer while mounted in a sealed enclosure. The second method uses only mechanical vibration and geometry of the radiator measured by using a laser triangulation scanner. The paper checks the reliability and reproducibility of conventional and the new methods and discusses the propagation of the measurement error on the T/S parameters using text box perturbation technique and other derived parameters (sensitivity).
Convention Paper 8075 (Purchase now)

P15-3 Modeling Acoustic Horns with FEA—David J. Murphy, Krix Loudspeakers - Hackham, South Australia, Australia; Rick Morgans, Cyclopic Energy - Adelaide, South Australia, Australia
Simulations for acoustic horns have been developed using Finite Element Analysis (FEA) in both ANSYS and COMSOL modeling software. The FEA method solves the ideal, linear wave equation, so the effects of nonlinearity and viscosity are not inherently simulated. Quarter models were used in each case as the acoustic horns were not axi-symmetric. The size and shape of the horns have been informed by longstanding design parameters. The simulation results have been compared with acoustic measurements, and discrepancies investigated. While it was found that beam angle (dispersion) characteristics were relatively robust, it was useful in both cases to improve the accuracy of the beam angle, SPL, and impedance simulations by the application of frequency dependent damping to models of the compression driver.
Convention Paper 8076 (Purchase now)

P15-4 Electroacoustic Measurements for High Noise Environment Intercom Headsets—Stelios Potirakis, Technological Education Institute of Piraeus - Aigaleo-Athens, Greece; Nicolas – Alexander Tatlas, University of Patras - Patras, Greece; Maria Rangoussi, Technological Education Institute of Piraeus - Aigaleo-Athens, Greece
Intercom headsets are mandatory communication apparatus in high noise environment (HNE) conditions. Although military intercom headsets are typically used under extreme environmental conditions, a standard performance evaluation method exists only for the earphone elements. A systematic methodology for the measurement and performance evaluation of HNE headsets has recently been proposed based on the use of Head and Torso Simulator (HATS), addressing both signal reproduction and noise reduction issues. In this paper an improvement of the specific method is proposed concerning the headset electroacoustic reproduction measurements. The proposed enhancement refers to the use of impulse response measurements for the extraction of the specific characteristics as a function of frequency.
Convention Paper 8077 (Purchase now)

P15-5 Phase, Polarity, and Delay or Why a Loudspeaker Crossover Is Not a Time Machine—Ian Dash, Australian Broadcasting Corporation - Sydney, NSW, Australia; Fergus Fricke, University of Sydney - Sydney, NSW, Australia
Phase delay and group delay functions are well known in lumped system theory but they are not well understood, particularly in the context of non-minimum phase lumped systems. This paper presents four paradoxes that arise from an overly-literal interpretation of the phase delay function. The paradoxes are very simply illustrated using the example of a first order loudspeaker crossover. A new system response model is presented to resolve these paradoxes. The model is extended to higher order systems and to non-minimum phase systems. Applications and implications for system analysis are discussed.
Convention Paper 8078 (Purchase now)

P15-6 Time and Level Localization Curves for a Regularly-Spaced Octagon Loudspeaker Array—Laurent S. R. Simon, Russell Mason, University of Surrey - Guildford, Surrey, UK
Multichannel microphone array designs often use the localization curves that have been derived for 2-0 stereophony. Previous studies showed that side and rear perception of phantom image locations require somewhat different curves. This paper describes an experiment conducted to determine localization curves using an octagonal loudspeaker setup. Various signals with a range of interchannel time and level differences were produced between pairs of adjacent loudspeakers, and subjects were asked to evaluate the perceived sound event's direction and its locatedness. The results showed that the curves for the side pairs of adjacent loudspeakers are significantly different to the front and rear pairs. The resulting curves can be used to derive suitable microphone techniques for this loudspeaker setup.
Convention Paper 8079 (Purchase now)