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By DanDaley
Scientific protocol calls for lots of
testing before a product is finally
assembled. However, in the highly
subjective and opinionated realm of
loudspeakers, testing has become not
so much an afterthought as an afterthe-fact
proposition in some instances.
The transducer and cabinet assembly of
each component in a line array are subjected
to plenty of testing as each element
is developed and connected, but
the dynamic and incrementally minute
nature of the line array itself tends to
get its final checks in situ, flying above
the crowd.
Routine Systems Testing BIZ
JBL has historically been a major
proponent of systems testing — during
the development of the VerTec line array
system at the turn-of-the-century
rigs were routinely set up in the parking
lot and on the roof to check ground
planes and other splays, and in one instance,
an entire system was set up in
an airplane hangar at Van Nuys airport
near the Harman Industries’ headquarters.
“This enabled JBL engineers to
validate correlations of predictive software
tools with actual measurements
of large-scale arrays, which is especially
important with line-array type system
formats,” recalls David Scheirman, JBL’s
vice president of tour sound.
“The issue with very large sound
systems is that the bigger they get, the
farther away you have to measure them
from and it can reach the point where it
becomes less and less practical to test
physically,” comments Paul Bauman,
JBL’s director of tour sound engineering.
Tips ‘n’ Tricks
Combating Feedback
Even though monitor placement is
simple, it is very important. Where you
place your monitors can affect the perceived
tone and be an important tool
in combating feedback. If you ask your
worship band players or singer where
they want their monitors placed you
may find that they have some very specific
ideas about placement. I like to
have my wedge set at about 10 o'clock
to my left. I play 12-string acoustic guitar
at my church and if I place the monitor
directly in front of me, there is a
good chance my guitar will feed back.
At 10 o'clock, I can hear the wedge and
I am off axis for resonance-induced
feedback from my guitar.
— Jamie Rio from his “Sound
Sanctuary” column in the October
2008 issue.
It’s a pragmatic and logistical problem,
but one rooted in ideology as much as
science. “Back in the early days of EASE
there was a debate over angular resolution,”
says Bauman. “The analogy to that
today is whether you can accurately extrapolate
far-field data from near field
measurements.”
A Small and Interesting Niche BIZ
This situation, along with the proliferation
of line arrays being used in applications
ranging from massive arenas
to small clubs, has created a small and interesting
niche, one that more and more
systems designers and component manufacturers
are coming to rely on. In the
1960s and ‘70s, Ron Sauro used to work at
NASA, measuring trajectories that would
help put Voyager, Pioneer and Apollo
spacecraft into space. One of the human
manifestations of the peace dividend,
Sauro now parses data about speakers in
his lab in Santa Clarita, Calif., where his
company NWAA Labs tries to bring some
order to a combination of tricky measurements
and marketing-speak. “It used to
be that you could measure key aspects,
like magnitude and phase, of a speaker in
a system fairly easily when most AP systems
took the form of clusters,” he says.
“Once the line array became popular, it
was slowly realized that it couldn’t be
measured accurately the same way. With
a cluster, you could take all of the far-field
information and trace it back to a single
point in space. But with line arrays, where
the point sources are multiple and highly
variable, you have to measure more and
from farther away to create a meaningful
set of data.”
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NWAA accomplishes this with its
MACH (Multi-Angle Computerized High-
Speed) testing system, which uses a proprietary
array comprised of 19 matched
Earthworks M-30 microphones and a
Linear X precision turntable capable of
0.1-degree accuracy. It simultaneously
samples impulse responses within an
anechoic chamber and uses these to
create loudspeaker radiation “balloons”
(a graph of a sound radiation pattern)
in a fraction of the time used by other
testing methods. This data is gathered
by a multi-channel version of EASERA
and is then converted to EASE V4, EASE
V3, CLF 1 and 2 formats for transmission
to the client or user. If you were to apply
the older methodology of taking 2,500
[impulse response] measurements to a
line array, it would take you a week,” he
says. Using MACH, he says they can do it
in less than an hour, yet still measuring
for every possible configuration of LF,
MF and HF boxes at any and all possible
angles, by rotating the box around the
axis of the driver.
Cutting Through the Clutter BIZ
While some of his clients are systems
designers seeking to cut through the
clutter of marketing materials masquerading
as spec sheets, the majority are
actually the speaker makers themselves,
including JBL, Meyer and EAW, seeking
to provide their customers a more valid
way to compare performance characteristics
before a system is hung. What
becomes an enormous amount of measurement
data is codified into a program
called Generic Listening Library
(GLL), that seeks to document and ar-
The Biz
Testing, Testing…
chive performance records of all types
of speakers.
The message, though, should be less
about the data than how it is used, says
Pat Brown, president of Synergetic Audio
Concepts (Syn-Aud-Con) in Greenville,
Ind., and its testing division, Electro-
Acoustic Testing Co., one of a handful
of independent testing facilities in the
sector. “There is good agreement on the
required data set for simple loudspeakers
with modeling as the stated objective,
[but]… it is more important that
the data be appropriate for the device
being tested,” Brown cautions. “Understanding
loudspeaker data is not trivial,
and comparing different loudspeakers
with a few ‘one number’ metrics such
as sensitivity or power handling can be
completely meaningless. Unfortunately,
this is often how the buying decision is
made, and this fact can affect how loudspeaker
specifications are determined
and published. Collecting the data is a
much easier task than conveying to the
end user what it means and how to use
it in a meaningful way.”
Testing at this level is likely to remain
a niche, albeit an intense one.
“There’s something to be said for having
an independent, impartial laboratory
do these kinds of measurements,”
says Bauman. “It’s reassuring to clients
like sound designers who deal with issues
like allocating the resources and
time needed to do it right, which is often
not practical even for large manufacturers
anymore.”
Dan Daley can be reached at ddaley@
fohonline.com
2008 NOVEMBER
47
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