Tech Briefs Magazine - October 2021 - 32a

DEMOCRATIZING SIMULATION
the problems come from a part of the
enclosure, or a part of the vent, that you
would not expect. A wooden model does
not show you exactly where the problems
are. " The L-Acoustics team came up with
an interesting way to work around this
problem. " Something we have done in
the past is to make some of the panels
in the box transparent. We would blow
smoke into the loudspeaker to enable us
to see the turbulence, " Horyn says.
While a see-through panel could
make a physical model more helpful, the
prototyping process remained a major
time sink. " When we design and build a
mockup, it takes several weeks between
drawing it and actual testing, " explains
Horyn. " And it would often take multiple
iterations to arrive at our design. "
FIGURE 5     
       
FIGURE 6      
         
     
significant acoustic losses of up to several
dB. Despite this risk, the potential
benefits of a resonator make it an
important tool for L-Acoustics, who strive
to fill massive spaces with sound.
" Our loudspeakers must perform at
a very high level of output, " says Yves
Pene, an acoustical engineer on Horyn's
team. " A resonator that is incorrectly
designed could lose up to half of its
potential output due to turbulence, so
it is really important that we design the
vent to work efficiently. "
» CUTTING WOOD,
SCULPTING CLAY, FILLING
SPEAKERS WITH SMOKE
" For several years, designing and
32a COMSOL NEWS
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testing vents has been a challenge for
development teams, " explains Horyn. " We
had no way of predicting precisely the
amount of loss created by an enclosure
with a high level of air displacement. "
This meant that the team had to build and
test wooden prototypes of every design
adjustment to either the enclosure or the
resonator vent. In some cases, they applied
clay to quickly change the shape of a vent's
opening or interior passages. This could be
a slow process - and even a completed
physical prototype would not give them all
the data they needed.
" Measuring acoustic loss and distortion
is interesting, but it does not always
give you an insight on where the
problems are, " says Horyn. " Sometimes,
» SIMULATION FOR CURRENT
AND FUTURE PROJECTS
To help refocus the L-Acoustics team's
efforts on acoustical engineering, rather
than woodworking, Yves Pene turned
to multiphysics simulation. His objective,
as explained in a 2020 research paper
presented to the Audio Engineering
Society (Ref. 1), was to model and
predict nonlinear acoustic loss in vented
port systems for a given loudspeaker,
enclosure volume, and port design. The
simulation incorporates the coupled
effects of the loudspeaker driver's motion
and the resulting fluid motion, including
turbulence and related phenomena. Pene
developed the model to test the effects of
four different speaker vent designs (Figure
4) on a given speaker and enclosure.
To validate the simulation results, they
followed up with experimental testing on
a speaker enclosure with removable vents.
These tests produced results that matched
the simulation's predictions remarkably
well: The predicted acoustic losses
deviated less than 1 dB from the actual
measured values of live testing. " We were
quite happy with the results, " says Pene.
Pene's successful simulation project
has revealed insights that could not
be achieved with prototyping alone.
Introducing simulation into the
L-Acoustics R&D workflow also promises
further benefits going forward. As
explained in the team's research report,
the simulation provided detailed velocity
and vorticity mapping throughout the
modeled enclosure and vent designs.
This provided data on exactly how
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Tech Briefs Magazine - October 2021

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