AES New York 2007
Acoustic Modeling, Part 2
Paper Session P15
Sunday, October 7, 1:00 pm — 5:00 pm
Chair: Geoff Martin, Bang & Olufsen a/s - Struer, Denmark
P15-1 Improvement of One-Dimensional Loudspeaker Models—Juha Backman, Nokia Corporation - Espoo, Finland
Simple one-dimensional waveguide models of loudspeaker enclosures describe well enclosures with simple interior geometry, but their accuracy is limited if used with more complex internal structures. The paper compares the results from one-dimensional models to FEM models for some simplified enclosure geometries found in typical designs. Based on these results it is apparent that one-dimensional models need to be refined to take some three-dimensional aspects of the sound field in close proximity of drivers into account. Approximations matched to FEM solutions are presented for enclosure impedance as seen by the driver and for the end correction of ports, taking both edge rounding and distance to the back wall into account.
Convention Paper 7253 (Purchase now)
P15-2 Simulating the Directivity Behavior of Loudspeakers with Crossover Filters—Stefan Feistel, Wolfgang Ahnert, Ahnert Feistel Media Group - Berlin, Germany; Charles Hughes, Excelsior Audio Design & Services, LLC - Gastonia, NC, USA; Bruce Olson, Olson Sound Design - Brooklyn Park, MN, USA
In previous publications the description of loudspeakers was introduced based on high-resolution data, comprising most importantly of complex directivity data for individual drivers as well as of crossover filters. In this paper it is presented how this concept can be exploited to predict the directivity balloon of multi-way loudspeakers depending on the chosen crossover filters. Simple filter settings such as gain and delay and more complex IIR filters are utilized for loudspeaker measurements and simulations, results are compared and discussed. In addition advice is given how measurements should be made particularly regarding active and passive loudspeaker systems.
Convention Paper 7254 (Purchase now)
P15-3 Intrinsic Membrane Friction and Onset of Chaos in an Electrodynamic Loudspeaker—Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia; Ivan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia
Chaotic state observed in an electrodynamic loudspeaker results from a nonlinear equation of motion and is driven by an harmonic restoring term being assisted by intrinsic membrane friction. This friction is not the smooth function of displacements but the sum of local hysteretic surface fluctuations, which give rise to its high differentiability in displacements, being responsible for onset of Feigenbaum bifurcation cascades and chaos. When an external small perturbation of low differentiability is added to the friction, another type of chaotic state appears, and this state involves period-3 window evidenced for the first time in these experiments.
Convention Paper 7255 (Purchase now)
P15-4 Damping of an Electrodynamic Loudspeaker by Air Viscosity and Turbulence—Ivan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia; Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia
Damping of an electrodynamic loudspeaker has been studied with respect to air turbulence and viscosity. Both quantities were evaluated as a difference of damping friction measured in air and in an evacuated space. The viscous friction dominates for small driving currents (< 10 mA) and is masked by turbulence for currents extending up to 100 mA. Turbulence contribution was evaluated as a difference of air damping friction at 1.0 and 0.1 bars, and it was studied for selected driving frequencies. Hot wire anemometry has been adopted to meet requirements of convection study from the loudspeaker, and obtained spectra were compared to measured turbulence friction, in order to trace the perturbation of emitted signal by turbulent motion.
Convention Paper 7256 (Purchase now)
P15-5 Energetic Sound Field Analysis of Stereo and Multichannel Loudspeaker Reproduction—Juha Merimaa, Creative Advanced Technology Center - Scotts Valley, CA, USA
Energetic sound field analysis has been previously applied to encoding the spatial properties of multichannel signals. This paper contributes to the understanding of how stereo or multichannel loudspeaker signals transform into energetic sound field quantities. Expressions for the active intensity, energy density, and energetic diffuseness estimate are derived as a function of signal magnitudes, cross-correlations, and loudspeaker directions. It is shown that the active intensity vector can be expressed in terms of the Gerzon velocity and energy vectors, and its direction can be related to the tangent law of amplitude panning. Furthermore, several cases are identified where the energetic analysis data may not adequately represent the spatial properties of the original signals.
Convention Paper 7257 (Purchase now)
P15-6 A New Methodology for the Acoustic Design of Compression Driver Phase-Plugs with Concentric Annular Slots—Mark Dodd, Celestion International Ltd. - Ipswich, UK, and GP Acoustics (UK) Ltd., Maidstone, UK; Jack Oclee-Brown, GP Acoustics (UK) Ltd. - Maidstone, UK, and University of Southampton, UK
In compression drivers a large membrane is coupled to a small horn throat resulting in high efficiency. For this efficiency to be maintained to high frequencies the volume of the resulting cavity, between horn and membrane, must be kept small. Early workers devised a phase-plug to fill most of the cavity volume and connect membrane to horn throat with concentric annular channels of equal length to avoid destructive interference . Later work, representing the cavity as a flat disc, describes a method for calculating the positions and areas of these annular channels where they exit the cavity, giving least modal excitation, thus avoiding undesirable response irregularities. In this paper the result of applying both the equal path-length and modal approaches to a phase-plug with concentric annular channels coupled to a cavity shaped as a flat disc is further explored. The assumption that the cavity may be represented as a flat disc is investigated by comparing its behavior to that of an axially vibrating rigid spherical cap radiating into a curved cavity. It is demonstrated that channel arrangements derived for a flat disc are not optimum for use in a typical compression driver with a curved cavity. A new methodology for calculating the channel positions and areas giving least modal excitation is described. The impact of the new approach will be illustrated with a practical design.
Convention Paper 7258 (Purchase now)
P15-7 A Computational Model for Optimizing Microphone Placement on Headset Mounted Arrays—Philip Gillett, Marty Johnson, Jamie Carneal, Virginia Tech Vibration and Acoustics Laboratories - Blacksburg, VA, USA
Microphone arrays mounted on headsets provide a platform for performing transparent hearing, source localization, focused listening, and enhanced communications while passively protecting the hearing of the wearer. However it is not trivial to determine the microphone positions that optimize these capabilities, as no analytical solution exists to model acoustical diffraction around both the human and headset. As an alternative to an iterative experimental approach for optimization, an equivalent source model of the human torso, head, and headset is developed. Results show that the model closely matches the microphone responses measured from a headset placed on a Kemar mannequin in an anechoic environment.
Convention Paper 7259 (Purchase now)
P15-8 A Simple Simulation of Acoustic Radiation from a Vibrating Object—Cynthia Bruyns Maxwell, University of California at Berkeley - Berkeley, CA, USA
The goal of this paper is to explore the role that fluid coupling plays on the vibration of an object, and to investigate how one can model such effects. We want to determine whether the effects of coupling to the medium surrounding a vibrating object are significant enough to warrant including them into our current instrument modeling software. For example, we wish to examine how the resonant frequencies of an object change due to the presence of a surrounding medium. We also want to examine the different methods of modeling acoustic radiation in interior and exterior domains. Using a simple 2-D beam as an example, this investigation shows that coupling with dense fluids, such as water, dramatically changes the resonant frequencies of the system. We also show that using a simple finite element model and modal analysis, we can simulate the acoustic radiation profile and determine a realistic sound pressure level at arbitrary points in the domain in real-time.
Convention Paper 7260 (Purchase now)
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