LSI Review June 2017
Road Test
VIA PROSOUNDWEB.COM
LINEA RESEARCH 44M20
Looking into
a new DSP
amplifier
platform.
by Craig Leerman
K-based Linea Research, for
years a designer and manufacturer of OEM power amplifiers
with sophisticated digital signal processing for several top pro audio companies,
has now launched products under its
own name. The Linea line includes 8- and
4-channel DSP amplifiers for both touring
and installation applications, as well as a
digital system controller.
Here we’re going to take a look at the
44M20, a 4-channel DSP amplifier for
live sound/touring. It’s housed in a 2RU
package specified as delivering (per channel) 1,500 watts at 8 ohms, 3,000 watts
at 4 ohms, and 5,000 watts at 2 ohms,
all channels driven. The class D amplifier
designed has a stated frequency response
U
The I/O facilities on the back panel of
the 44M20.
of 7 Hz – 30 kHz (-2.5 dB) at 4 ohms, low
inter-channel crosstalk (better than -85
dB at 1 kHz), and a low total harmonic
distortion rating of <0.05 percent (typical
at 4 ohms with a 1 kHz signal).
Analog and AES inputs are standard,
with Dante inputs an option. (The unit
provided for this evaluation had all
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LIVE SOUND INTERNATIONAL
JUNE 2017
three.) It’s only 14 inches deep behind
the rack ears and weighs in at a scant 27.5
pounds. Note that while light in weight,
if the amp is mounted in a mobile rack,
it’s important that the rear is supported
with the rear rack mounting kit.
The front panel offers input and output meters as well as individual channel
output mute buttons. A nicely sized LCD
screen occupies the middle, flanked by six
menu buttons and two rotary encoders.
The bottom is dominated by a large air
inlet covered with an intake filter that’s
easily removed for cleaning.
The rear panel provides all I/O, including Neutrik SpeakON connectors for
loudspeaker outputs. Each amplifier
channel has an XLR input and output,
and there’s also AES I/O. Dante primary
and secondary ports and a RJ45 port
for computer control are located next
to a recessed software reset button and
Phoenix connector that can relay fault
information. For power, a 32A Neutrik
PowerCon-type locking AC connector is
provided. All Linea models are designed
to operate on 50/60 Hz AC power, and the
power supply automatically configures
itself for either 115- or 230-volt nominal
voltage at turn on.
FRESH APPROACH
The processing offers a new way of ordering and grouping channels called Drive
Modules that provide a more loudspeak-
Linea Research 44M20 DSP amplifier.
er-centric approach to controlling, designing and recalling configurations. A Drive
Module consists of different “blocks” of
DSP, one for the input and several for the
outputs that are used for control and monitoring of the associated loudspeakers.
Further, presets can be broken apart
into components, allowing any output to
be used for any loudspeaker or even specific transducer in a system. For ease of
use, Overlay Groups allow various input
parameters to be adjusted in all modules
in a group while maintaining independent
parameter values across each group. For
example, EQ could be adjusted for every
group without having to access each channel’s Drive Module.
In addition to gain, EQ, and delay
parameters, the software also provides
access to a new type of crossover filtering
called LIR. This response filtering results
in a linear phase crossover that has a constant delay regardless of frequency. The
shape of the LIR filter is quite similar to a
4th order or 24 dB/octave Linkwitz-Riley
filter, and the factory states it maintains
zero phase difference between the adjacent bands across the crossover region
to keep the polar response “rock steady.”
Control of the 44M20 is provided by the
System Engineer PC application that offers
features such as flexible management of
presets and overlay grouping of mutes,
gains, delays, and EQ across an entire
sound system. In addition to the DSP, each
output can be optimized to drive either a
low impedance load (8, 4 or 2 ohms) or
a constant voltage setting (25-, 70- and
100-volt line) in the output menu.
www.ProSoundWeb.com
POWER TO SPARE
Unpacking the unit from the box, I was
immediately impressed with the power
to weight ratio. The 44M20 only weighs
about 25 pounds yet can put out 20,000
watts? Whoa. And that’s not a “peak” or
“burst” power number; the factory states
that the amp can deliver 5,000 watts at
2 ohms per channel with all channels
driven simultaneously. Back when I
started in pro audio, my first real amp
rack contained four amps that weighed in
at more than 200 pounds while delivering
2,400 watts in total.
Our company warehouse manager Wes
and I set up a passive loudspeaker system
so we could give the unit a listen. It was
easy to dial in the DSP. First we hooked
up a few full-range loudspeakers for critical listening test, and the loudspeakers sounded noticeably better with the
44M20 than with the 15-year-old amp
technology we currently use it.
Next, we adjusted the DSP and then
hooked up a couple of subwoofers. With
all four channels running, we played some
bass heavy electronic music to see if the
bass through a pair of channels would
make the amplifier sag a bit. But it just
chugged along with the subs thumping
and the tops sounding great. There was
also very little heat coming out of the
amp. Wes was really impressed and placed
the sonic quality at the same level as
some studio monitors that he’d recently
mixed a project with. We’ve had the loudspeakers for years and have never heard
them sound as good.
We also tested the Dante networking
with one of our Soundcraft mixers as well
as a Mackie DL32R compact rack-mount
mixer also in the shop for evaluation. I’m
a big fan of Dante and have switched to
it instead of analog as much as possible. Both mixers and the laptop running
Dante controller found the amplifier and
easily patched it into the network.
GENUINE PERFORMANCE
Confident in the capabilities of the
44M20, the next step was to take it to
www.ProSoundWeb.com
Control is
provided by
the System
Engineer
application.
some gigs. At a corporate meeting where
we normally use powered 15-inch loudspeakers, we swapped in a pair of passive 15-inch (also horn loaded) models
in order to drive them with the amplifier. Rik Kirby of Allied SMD (alliedsmd.
com), the North American distributor for
Linea, had included a PowerCon-to-Edison cable with the unit so we could plug
the it into a single outlet for testing. Of
course, we weren’t going to be able to
run it at full power from a 15-amp wall
circuit, but for this average-sized room,
we only needed a few hundred watts to
adequately drive the PA.
The 44M20 made that pair of passive
loudspeakers sound great, and sat in the
corner running cool all day. If there were
more time available, we could have set the
DSP to match the loudspeakers perfectly,
but the production ended up being a rush
so we just ran two channels of the amp,
full range.
Supporting a live band at an event
came next. Basically, we deployed the
same system configuration that we’d set
up in the shop – two full-range top boxes
pole-mounted over two subs. In this case,
however, the loudspeakers were higher
end, and they’re normally driven by three
amplifiers (two of them bridged running
one per sub at 4 ohms and the other running the tops in stereo). In contrast, just
the single 44M20 supplied 3,000 watts
at 4 ohms for each sub and 1,500 watts
for each top, more audio power than the
three amps we normally use, plus the
DSP is built in. It also made the rig sound
noticeably better.
I’m confident that if we bought our
current amp rack components new, the
cost would be more than the 44M20.
Using it to drive the mains and a smaller
Linea 4-channel model for monitors
would make for a small, light and therefore easy-to-transport power solution
that could take the place of two of our
16-space racks.
The band sounded great through the
rig, and during sound check the singer
stood by the mix position and commented how fantastic the rig sounded.
Before the show and during the breaks
we played some of the test tracks used
at the LSI Loudspeaker Demos. They
sounded amazing, so much so that I
even listened to Jennifer Warnes’ “The
Hunter” for the 17,345th time with a
smile on my face. Suffice to say that the
unit worked flawlessly and my creaky
old back appreciated not having to move
around a heavy amp rack.
The Linea Research 44M20 represents
the highest caliber of professional audio
technology. It very well could be the
best sounding power amplifier I’ve ever
heard. It’s also flexible, not only in terms
of the DSP but that it can be optimized
for 70-volt systems and networked seamlessly in live and installed systems, large
and small.
U.S. MSRP: $7,500 LSI
Senior contributing editor Craig Leerman
is the owner of Tech Works, a production
company with offices in Las Vegas and Reno.
JUNE 2017
LIVE SOUND INTERNATIONAL
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