Session F Sunday, May 13 9:00  13:00 hr Room C/D Loudspeakers, Part 2Chair: Neville Thiele, University of Sydney, Sydney, Australia 9:00 hr F1 The software we will describe allows the study and
analysis of direct radiation loudspeaker systems of one or multiple ways and
with different configurations in the woofer one, by means of computer
simulation, based on electroacoustical analogous circuits. This program allows
simulating the electrodynamic loudspeaker behavior from the electrical,
mechanical and acoustical point of view, and could get information about
different variables frequency response. 9:30 hr F2 The directional properties of horn devices are
governed by the wave frontís shape presented at the mouth. An analysis of the
sound pressure distribution across the horn's mouth that we call Pressure
Distribution Mapping could certainly be helpful to understand how the wave
front is shaped there. Moreover, this could help to understand what happen in
some particular circumstances. For example midrange beaming or high frequency
mouth diffraction phenomena are two well known obstacles to overcome designing
a broad band constant directivity horn. The method forwarded by us in the
previous work is here extended to some different cases and improved in the data
processing. The results that come out of such analysis will be shown through
graphic illustrations. Presented will be the results obtained performing
measurements upon real devices correlated to traditional directivity plots as
well. 10:00 hr F3 An approach for simulating transient structural wave
propagation in loudspeakers is described. The Finite Element Method is used for
spatial discretization and the Laplace transform for the time solution. The
accuracy of the spatial discretization is verified by simulating the acoustic
frequency response of a loudspeaker and comparing the results with measured
data. A damping model is introduced that approximates standard hysteretic
damping and yet can be used directly in both the time and frequency domains.
The overall approach is verified by comparing laser measured and simulated
results of the transient structural response of a loudspeaker to an
impulselike excitation. Finally, structural energy is plotted and discussed. 10:30 hr F4 Although there is no question that the implementation of a
parallel crossover network represents the most useful and flexible approach to
the electroacoustical transducer matching in a loudspeaker system, there is
also no doubt that seriestype crossover networks can provide the designer with
some interesting features. Unfortunately, the conventional formulae are
restricted to the case where the impedance loads, representing the drivers, are
equal to each other, therefore limiting the application range. This work is
intended to explore in more detail the series crossover network topology,
presenting more general formulae and showing the advantages and disadvantages
with respect to a parallel solution. In this paper, first to ìlessthansecondî
order circuit realizations will be considered. 11:00 hr F5 It is possible to arrange loudspeakers in such a way that
only one lobe emits from the array. This lobe can have an arbitrary beam width
and to a certain extent an arbitrary beam shape. Because of this control over
the beam, narrow beam widths can be made where wave fronts travel coherently
200 meters or more. It is possible now to cover an area below and in front of
the array from almost zero to 200 meters with even directsound distribution of
+/ 3 dB, where the frequency response is only dependant on the transducer used
and the air absorption. This eliminates the colorationeffects due to side or
grating lobes. 11:30 hr F6 A new three band
loudspeaker/room correction system has been designed in order to reveal what
room acoustic properties and psychoacoustic relations are necessary and
sufficient to consider. Most parameters are variable, and the system is
designed to enable realtime implementation. A small scale listening test has
revealed that even when operating on highend audio equipment and employing a
well damped listening room, improvements in reproduction quality can be
achieved. Also in a listening position far away from the optimal and corrected
one, some improvement is observed. 12:00 hr F7 This work investigates experimentally the effect a porous
layer on the acoustic response of distributed mode loudspeakers (DMLs), which
are manufactured under license from NXT plc. The experiments were carried out
in an anechoic chamber. The results suggest that a porous layer between a rigid
base and a DML panel can considerably alter the acoustic emission in the
nearfield and in the farfield. This is typically illustrated by a reduction
in the level of fluctuations in the emitted acoustic pressure spectra. These
fluctuations are normally associated with interference between the sound
emitted by the front surface of the speaker and by that emitted from the back.
The results also suggest that the interference pattern in the air gap is
altered by the porous layer, so that some individual resonances in the acoustic
pressure spectra which inevitably occur between the rigid base and the
vibrating plate can appear suppressed. A numerical simulation was carried out
to model this effect. 12:30 hr F8 A denominator of a transfer
function of a symmetrical bandpass loudspeaker system can be presented as a
product of three or four second order polynomials. Every polynomial can
represent the denominator of the transfer function of an electrical filter. The
product of remaining polynomials forms the denominator of the transfer function
of a nonsymmetrical loudspeaker system. Then, various combinations of these
polynomials give various possibilities of realization of the entire system.

