Session D Saturday, May 12 13:30 - 18:00 hr Room C/D
Loudspeakers, Part 1
Chair: David Clark, DLC Design, Wixom, MI, USA
13:30 hr D-1
Comparison of Non-Linear Properties of Closed, Vented and Passive-Radiator
Loudspeaker Boxes
Bronislaw Zoltogorski
Wroclaw University of Technology, Wroclaw, Poland
The basic types of
loudspeaker boxes have been compared with regards to non-linear distortions
introduced to radiated acoustical signal. For given driver characterized by
small signal parameters and additional four coefficients of Bl and stiffness
non-linear models, the frequency characteristics of SPL and THD have been
calculated by numerical integration of a non-linear differential equation set
corresponding to the electrical equivalent circuit. The submitted MATHCAD
programs enable to design the non-linear characteristics of analyzed
loudspeaker system.
Printed Paper not available
14:00 hr D-2
Loudspeaker Litz Wire
Steven Hutt
Harman/Becker Automotive Systems, Martinsville, IN, USA
Studies of loudspeaker
components most often concentrate on the functions that add or detract from the
acoustically measurable performance aspects of loudspeakers - such as cones,
suspensions, or magnet and motor assemblies.
On the other hand, application of litz wire into the loudspeaker design
is not well documented. Yet the litz
wire has a profound impact on reliability and has a propensity to cause
problems such as unacceptable extraneous noise. After a review of classical theory on the vibration of strings,
bars and elasticity one will surmise that understanding the vibration of litz
wire is not trivial. This paper reviews a loudspeaker case study and the
ramifications of using behaved and not so well behaved litz wire.
Paper 5303
14:30 hr D-3
Line Arrays: Theory
and Applications
Mark Ureda
JBL Professional, Santa Ana, CA, USA
Line arrays of
loudspeakers are often employed to provide increased directivity, generally in
the vertical plane. For improved performance, contemporary line arrays employ
specially designed loudspeaker elements to provide a nearly continuous line
source. However, even these may have
�imperfections� relative to a perfect line source. This paper provides
mathematical models to evaluate the directivity response of line sources and to
quantify the effects of certain imperfections.
Paper 5304
15:00 hr D-4
Crossover Systems in
Digital Loudspeakers
Simon Busbridge (1), Yaxiong Huang (1) & Peter Fryer (2)
University
of Brighton, Brighton, UK
B&W
Loudspeakers, Steyning, UK
A digital loudspeaker is
one that does not contain any form of embedded digital to analogue
converter. From a consideration of the
mathematical operations describing the digital to analogue conversion process
in a digital loudspeaker, it is concluded that n identical analogue filters (where n is the number of bits) separately filtering each bit driver
offers a practical alternative to digital signal processing. The implementation of a multiple driver
multiple voice coil digital loudspeaker is described. The effect of component
tolerances in the crossover and compatibility with the requirements of current
drive are evaluated. The interactions between the motion emf, driving current
and mutual coupling emf�s are considered. It is concluded that this method of
crossover implementation is both viable and achievable.
Paper 5305
15:30 hr D-5
Sound Directivity
Control using Striped Panel Loudspeaker
Marko Antila (1), Vesa V�lim�ki (2) & Jari Kataja (1)
VTT
Automation, Tampere, Finland
Helsinki
University of Technology, Espoo, Finland
The sound radiation
properties of a striped panel loudspeaker are modified in this study. The panel
loudspeaker is based on Electromechanical film (EMFi) and consists of 14
individual sound radiating areas in form of narrow stripes. Each stripe can be
driven individually so that the panel radiation pattern can be modified and it
can be used as a directivity-controlled sound source in audio applications. The
performance of the panel was analyzed using an acoustical boundary element
method (BEM) model. For real-time directivity control, an algorithm was
developed to process the input signals to gain appropriate radiation patterns.
The measurements carried out in anechoic conditions were used to verify that
the striped EMFi panel operates according to the simulations and that it
produces the desired directivity pattern.
Paper 5306
16:00 hr D-6
Phase Considerations
in Loudspeaker Systems
Neville Thiele
University of Sydney, Sydney, Australia
The effect of phase
rotation on the reproduced quality of an audio signal is well known. However,
the effect of phase rotations in the responses of individual drivers on the
amplitude response of a multi-way system is often misunderstood. The paper
quantifies this effect and, in showing that it is similar in nature to the
better understood problem of time alignment, demonstrates how similar remedies
may be applied to both effects together. It also shows how lowering the low
frequency cutoff of a loudspeaker system can reduce its group delay errors in-band.
Paper 5307
16:30 hr D-7
Fast and Accurate
Measurement of the Linear Transducer Parameters
Wolfgang Klippel &
Ulf Seidel
Klippel, Dresden, Germany
A new measurement
technique is presented for the estimation of the linear parameters of the
lumped transducer model. It is based on the measurement of the electrical
impedance and the voice coil displacement using a laser sensor. This technique
identifies the electrical and mechanical parameters directly and dispenses with
a second measurement of the driver using a test enclosure or an additional
mass. Problems due to leakage of the enclosure or the attachment of the mass
are avoided giving accurate and reliable results. The measurement of the
displacement also allows identification of the mechanical compliance versus
frequency (explaining suspension creep) which is the basis for predicting the
radiated sound pressure response at low frequencies precisely. The linear
parameters measured at various amplitudes are compared with the results of
large signal parameter identification and the need for nonlinear transducer
modeling is discussed.
Paper 5308
17:00 hr D-8
Far-Field Loudspeaker
Interaction: Accuracy in Theory and Practice
Justin Baird, John Meyer & Perrin Meyer
Meyer Sound Laboratories, Berkeley, CA, USA
The "Far-Field"
model of loudspeaker interaction is a widely used technique to model the sound
pressure radiated from arrays of loudspeakers. We will provide a quick but
thorough introduction to the mathematical foundation of the far-field model,
and how the model compares, with regards to accuracy and computational
efficiency, to other formulations such as series solutions and boundary element
methods. We present data from a series solution of a model spherical
loudspeaker, and compare this mathematical model to actual high-resolution
measurements. Using this model loudspeaker, we discuss methods for calculating
and measuring accurate loudspeaker far-field polar (or directivity) patterns,
and we discuss how the accuracy of the far-field polar patterns affect the accuracy of the far-field model.
Paper 5309
17:30 hr D-9
Speaker Auralization
- Subjective Evaluation of Nonlinear Distortion
Wolfgang Klippel
Klippel, Dresden, Germany
A new auralization
technique is presented for the objective and subjective assessment of drivers
in the large signal domain. Using the results of the large signal parameter
identification a digital model of the particular driver is realized in a
digital signal processor (DSP) to simulate the sound pressure output for any given
input signal (test signal, music). This technique combines objective analysis
and subjective listening test to assess the linear and distortion components in
real time. This valuable tool shows the impact of each distortion component on
sound quality and allows driver optimization with respect to performance, size,
weight and cost.
Paper 5310
