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AES Amsterdam 2008
Loudspeakers - 2
Paper Session P7
Sunday, May 18, 09:00 — 11:30
Chair: Ronald Aarts, Philips Research - Eindhoven, The Netherlands
P7-1 Low-Frequency Extension of Gated Loudspeaker Measurements—Juha Backman, Nokia Corporation - Espoo, Finland
The free-field response of a loudspeaker system can be approximated through a gated measurement, made in a sufficiently large space. The frequency resolution is nominally determined by the time gap between the direct sound and the first reflection, but the actual low-frequency accuracy of gated measurements is reduced also by the group delay of the loudspeaker itself. The group delay at low frequencies may cause a large fraction of the energy sound radiation to be cut off, underestimating the low-frequency response. A method is presented to estimate the approximate low-frequency response from the impedance measurement of the loudspeaker and to use the response to pre-process the acoustical measurement to improve the accuracy of the gated measurement.
Convention Paper 7353 (Purchase now)
P7-2 Measurement and Fourier-Bessel Analysis of Loudspeaker Radiation Patterns Using a Spherical Array of Microphones—Filippo M. Fazi, Vincent Brunel, Philip A. Nelson, University of Southampton - Highfield, Southampton, UK; Lars Hörchens, Delft University of Technology - Delft, The Netherlands; Jeongil Seo, Electronics and Telecommunications Research Institute (ETRI) - Daejeon, Korea
Loudspeakers are widely used in three-dimensional sound field reconstruction systems, but their spatial directivity features are relatively little-known. In this paper a hemispherical array of 40 microphones was designed and built in order to measure the pressure field radiated by different commercially available loudspeakers. The spatial samples of the acoustic pressure were processed in order to estimate the truncated Fourier-Bessel expansion of the sound field, which allows the reconstruction of the 3-D radiation pattern. An analysis of the errors involved in the estimation was also performed with a numerical model of the array.
Convention Paper 7354 (Purchase now)
P7-3 Turbulent and Viscous Air Friction in the Mid-High Frequency Loudspeaker—Ivan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia; Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia
Mid-high frequency loudspeaker with resonant frequency f = 982 Hz has been studied in atmospheres of air, He4, D2 and H2 at pressures ranging 0-1 bar. The measurements of viscous and turbulent contributions to the friction entering Q-factor showed significant difference as compared to a low frequency loudspeaker. The resonant frequency in air is considerably lower in an evacuated space than at 1 bar, and this differs from the low frequency loudspeaker, when the opposite is true. Measurements showed that imaginary part of viscous friction in Navier-Stokes equation is dominant, while contribution of the real part to the friction term is less significant, and Navier-Stokes equation reduces to the Stokes form ?p=-µ?vr , when imaginary part of the viscous force reduces effective vibration mass, which in turn enables operation of the loudspeaker at high frequency. The data were interpreted in terms of Greenspan theory of the piston radiator.
Convention Paper 7355 (Purchase now)
P7-4 Modeling of an Electrodynamic Loudspeaker including Membrane Viscoelasticy—Antonio Petosic, Ivan Djurek, University of Zagreb - Zagreb, Croatia; Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia
The model is proposed based upon viscoelastic properties of the loudspeaker membrane, and properties considered include stress-strain hysteresis, creeping effect, initial stress effect, and appearance of the temperature fluctuations on the membrane surface. The creeping displacement response dependent on the step-like excitation current has been measured on different loudspeaker configurations, and listed effects were analyzed in terms of the N-order Bennewitz-Rötger differential equation, commonly used for description of the system of vibrating viscoelastic body. The main parameter in this equation is inverse stress parameter which connects friction and restoring term in the loudspeaker vibrating system.
Convention Paper 7356 (Purchase now)
P7-5 On a Novel Concept of Membrane Suspension in an Electrodynamic Loudspeaker—Danijel Djurek, Alessandro Volta Applied Ceramics (AVAC) - Zagreb, Croatia; Ivan Djurek, Antonio Petosic, University of Zagreb - Zagreb, Croatia
A laboratory model of an electrodynamic loudspeaker has been realized with the membrane suspended on a hollow elastic torus positioned in the bottom of the membrane, close to the voice coil. This geometry removes the torque in the membrane coming from the maximum possible distance of the suspension on the outer rim from the voice coil. The suppressed torque results in the suppression of the Bessel vibration modes, which generate stochastic deformation tilts on the membrane surface. Such tilts contribute to the intrinsic friction of the membrane, and their absence results in minor viscoelastic losses. Lateral rigidity of the torus is sufficient for operation of the loudspeaker without centric fixation.
Convention Paper 7357 (Purchase now)
Last Updated: 20080612, tendeloo