Ten Line Array Myths by Apocalypse Acoustics
1. Line arrays are a fad
Not
true. Line arrays offer cogent means to increase coverage and SPL while
reducing temporal distortion and the architectural footprint of the
loudspeakers. Unless you are a speaker manufacturer without one, what's not to
like?
2. J-Arrays improve the vertical coverage
J-arrays
consist of two totally different loudspeaker arrays. They perform poorly
because of the withering discontinuity where curved and straight segments join.
3. Down-fills are a good way to cover 'down front'
Like
the doomed pilot who runs out of altitude and ideas, we sometimes run out of
both time and viable alternatives. But like the J-Array, using down-fill boxes
splices completely different loudspeakers to the main
array, creating interference where
Coverage conjoins.
4. Split
processing can optimize J-Arrays
This bolsters the
sales of DSP devices, but we can't fix directivity discontinuities with
DSP. Curved and
straight arrays have radically different vertical directivity characteristics and
should not be connected together.
5. Simulations
show the best way to configure line arrays
Simulation programs
are subject to the same human errors and manipulations that haunt every complex
software, only more so. Most programs are based upon assumptions and constructions
that fail to recognize the effects of discontinuities in array shapes. Use simulations
with care, but don't recommend or construct an array that has a physical discontinuity
just because a simulation shows appealing coverage representations – it isn't
possible.
6. Configurable
horizontal coverage improves spatial uniformity
Configurable
horizontal coverage seems like a good idea, but we cannot achieve
Directivity-matched
transitions through crossovers while making wave guide mouth
Openings smaller to
narrow the horizontal coverage. The result is irregular directivity frequency and
inconsistent frequency response in the critical middle and upper middle frequencies.
Efforts to 'fix' the frequency response with filters come at the expense of spatial
uniformity.
7. Each
venue requires its own unique DSP
This stems from the
misconception that observed misbehavior is caused by room
Acoustics and that
DSP can somehow rescue the day. Both assumptions are false.
Most misbehavior
is either the loudspeakers or the arrays, and DSP has no effect on
Room acoustics
anyway. Use equalization appropriately.
8. Tried-and-true
audio practices perform well with line arrays
Most 'tried and
true' practices don't perform as well as we'd like to think they do, and
They are less
likely to perform well with line arrays. Best results will always come from
Careful
cause-and-effect analysis before postulating solutions.
9. High
sound levels from line arrays are OK
If the sound
leaving the loudspeakers is 'clean' there won't be any distortion, right?
Wrong. Three types
of acoustic distortion are more significant in live sound than all
Others and line
arrays have a propensity for one of them.
10. Line
arrays radiate cylindrical sound fields
All that can be
said in support of this thesis is that the near field of a line array is an
Interference field
that roughly follows the frontal aspect of the loudspeakers. Inverse
Square law has not
been abrogated. The far field acts like that of any other loudspeaker.
All
of these myths are fallacious
They are either
untrue, or require narrow context setting to be true. Some are the result of
faulty understanding of the basic mechanics of how line arrays work and some
are deliberate misrepresentations. Nevertheless, they are the cornerstones of
line array folklore that are responsible for much of what sounds bad today.
Fortunately, practicing good science will always
be easier than fumbling bad science.
Why Array?
Arrays
serve to increase, decrease or re-shape coverage and/or increase the sound
Pressure
level. Other than these, arrays have no useful purpose.
Loudspeakers
that are physically offset from one-another with conjoining coverage are a
source of temporal distortion – combing and time smear in three dimensions that
cannot be 'fixed' with one-dimensional solutions.
That
some loudspeakers can be mounted closer to one-another, and that some might have
less coverage overlap than others only reduces combing and time smear.
Minimum
temporal offset results from small, tightly packed sources. Small sources have low
directivity and 'soft' pattern edges, increasing coverage overlap and temporal distortion.
High-directivity sources are big – separating the sources in space and time, which
also increases temporal distortion.
Line
arrays optimize the ability to conjoin coverage of a plurality of like sources
to
Produce
minimal temporal offsets in the direction of coverage, but they cannot repeal the
realities of time and space.
Why Line Arrays?
Line
arrays enable high sound levels, when compared to traditional multi-way systems. Due to their
greater length, line arrays maintain high vertical directivity to much lower frequencies.
• Improved direct-to-reverberant sound ratios in enclosed spaces
• Reduction of atmospheric interference effects out-of-doors
Line
arrays can be constructed to provide optimally wide vertical coverage to meet
Special
auditorium needs, e.g., balconies. They can also be shaped to provide tapered vertical coverage for
very deep auditoria, long throws and low trim heights.
Line
arrays lack one dimension that is responsible for temporal distortion in large
sound systems.
Extracts
from Mark
Engebretson: Designing & Deploying Line Arrays.
For further Information call us at +919848083140 or email us at apocalypse@mail.org
