Friday, October 10 3:30 pm 5:00 pm
Session Z3 Posters: Loudspeakers
Z3-1 Adjusting A Loudspeaker to Its Acoustic EnvironmentThe ABC SystemJan Abildgaard Pedersen, Bang & Olufsen a/s, Struer, Denmark
This paper presents a system for adapting a loudspeaker to its position and to the acoustic properties of the listening room: the ABC room adaptation system. Adaptive Bass Control (ABC) measures the acoustic radiation resistance seen by the bass drive unit and calculates a digital filter, which is inserted in the signal path before the power amplifier. The radiation resistance is calculated from measurements of sound pressures at two different positions in front of the bass drive unit. The measured radiation resistance is compared to sound pressure measurements at different listening positions. The ABC system has been found to provide a room adaptation, which is globally valid throughout the listening room, i.e., all listening positions benefit from this system.
Z3-2 Lamps for Loudspeaker ProtectionScott Dorsey, Kludge Audio, Williamsburg, VA, USA
Incandescent lamps have been used for over 50 years as loudspeaker protection devices, but a large amount of misinformation about them exists. The author measures static and dynamic parameters of over 30 types of auto lamps, as well as tests some types for consistency between manufacturers and production. The results contradict a lot of the common wisdom about using lamps for protection and show serious linearity problems even at low operating levels.
Z3-3 Hey Kid! Wanna Build a Loudspeaker? The First Ones FreeSteven Garrett, Penn State University, State College, PA, USA; John F. Heake, Naval Surface Warfare Center, Philadelphia, PA, USA
Penn State University recently instituted a first year seminar (FYS) requirement for every student. This paper describes a hands-on FYS on audio engineering that has freshmen construct and test a two-way loudspeaker system during eight two-hour classes. Time and resource constraints dictated that the speaker system must be assembled using only hand tools and characterized using only an oscillator and digital multimeter. The cost of the entire system could not exceed $60/side. This paper describes the speaker system, made primarily from PVC plumbing parts, and the four laboratory exercises that the students perform and document that are designed to introduce basic engineering concepts including graphing, electrical impedance, resonance, transfer functions, mechanical and gas stiffness, and nondestructive parameter measurement.
Z3-4 Loose Particle Detection in LoudspeakersPascal Brunet, Listen, Inc., Boston, MA, USA; Evan Chakroff, Tufts University, Medford, MA, USA; Steve Temme, Listen, Inc., Boston, MA, USA
During the loudspeaker manufacturing process, particles may become trapped inside the loudspeaker, resulting in a distinctive defect that is easily heard but difficult to measure. To give a clearer view of the problem, time-frequency maps are shown for some defective loudspeakers. Based on this analysis, a reliable testing procedure using a swept-sine stimulus, high-pass filter, and RMS-envelope analysis is presented. Further possible enhancements and applications of the method are listed.
Z3-5 Radiation of Sound by a Baffled DML-Panel Near a Porous LayerElena Prokofieva, University of Bradford, Bradford, UK
Theoretical analysis of the problem of an elastic rectangular vibrating panel placed into a baffle in the vicinity of a porous layer has been conducted. Numerical results were obtained from a special computer program written in Matlab 6.0. It has been found that the presence of the porous layer considerably alters sound emission by the panel. The effect of the porous layer characteristics as well as the air gap width between the vibrating panel and the porous layer on the acoustic pressure and surface velocity was investigated.
Z3-6 Practical Application of Linear Phase Crossovers with Transition Bands Approaching a Brick Wall Response for Optimal Loudspeaker Frequency, Impulse, and Polar ResponseJustin Baird, David McGrath, Lake Technology, Sydney, New South Wales, Australia
Conventional crossover design methods utilize traditional frequency selective networks to combine multiple transducers into a single full-bandwidth system. These traditional networks, whether they are implemented in analog or digital form, exhibit large transition bands and suffer from phase distortion. These characteristics result in poor frequency, impulse, and polar responses. A practical crossover implementation is presented that removes the detrimental effects of transition bands and phase distortion. This method implements linear phase crossovers whose transition bands approach a theoretical ideal brick wall response. Comparisons to conventional crossovers will be presented. Applications to large scale array optimization are also discussed and presented.
Z3-7 Practical Benefits and Limitations of Digitally Steered ArraysWilliam Hoy, David Gunness, Eastern Acoustic Works, Inc., Whitinsville, MA, USA
The capability of digitally steered line arrays to create directional patterns of varying beamwidth, and to steer those patterns off the primary axis of the device is well known. However, significant additional benefits may be realized with nontraditional coverage patterns and by exploiting the horizontal invariance of the vertical pattern to more precisely cover typical audience areas. The practical limits of off-axis steering and beamforming will also be characterized, so that practitioners may asses the potential impact of any unintended directional artifacts.
Z3-8 The Development of a Forward Radiating Compression Driver by the Application of Acoustic, Magnetic, and Thermal Finite Element MethodsMark Dodd, Celestion International Ltd. Ipswich, Suffolk, UK
A compression driver with an annular two-slot phase-plug coupled to the convex side of a hemispherical diaphragm is introduced. Magnetic and thermal domains are modeled using static and transient finite element methods (FEM). Structural and acoustic domains are modeled by finite elements with boundary elements used to model free space. Structural and acoustic elements are fully coupled to both each other and the boundary elements. The application of these FEM techniques to the optimization of compression driver performance is discussed and illustrated with results. The limitations of plane-wave tube measurements are also mentioned and illustrated with FEM and measured results.
Z3-9 Comparison of Direct-Radiator Loudspeaker System Nominal Power Efficiency vs. True Efficiency with High-Bl DriversD. B. (Don) Keele, Jr., Harman/Becker Automotive Systems, Martinsville, IN, USA
Recently Vanderkooy et al. considered the effect on amplifier loading of dramatically increasing the Bl force factor of a loudspeaker driver mounted in a sealed-box enclosure. They concluded that high Bl was a decided advantage in raising the overall efficiency of the amplifier-speaker combination particularly when a class-D switching-mode amplifier was used. This paper considers the effect of increasing Bl on the efficiency of the driver only. Two efficiency definitions are considered: the traditionally-defined nominal power transfer efficiency (acoustic power output divided by nominal electrical input power) and the true efficiency (acoustic power output divided by true electrical input power). Raising Bl dramatically increases the drivers true efficiency at all frequencies but severely attenuates the nominal power efficiency bass response. Traditional design methods based on nominal power transfer efficiency disguise the very-beneficial effects of dramatically raising the drivers Bl product.