QSC power amplifiers have been a staple of large rock
’n’ roll concert systems for decades — and for
good reason. The amps are extremely powerful, they sound good, and
they're rugged enough to stand up to the abuses of the road. But
does their pedigree as roadworthy workhorses make them suitable for
use in small venues and in the racks of weekend-warrior musicians?
I decided to find out.
I test-drove the RMX 2450, the largest and most powerful
amplifier in QSC's new RMX series. Rated at 750W per channel into 4
(1,200W per channel into 2), the amp is just the right size to
light up a midsize club speaker system all by itself, or to be used
as part of a triamplified touring rack. When providing sound for
clubs, I use a set of Community XLT-55 2515 bottoms and XLT-65
3-way tops, which you can either triamplify or power with a single
amplifier in passive crossover mode. I tested the RMX 2450 in both
configurations.
HEAVY METAL
The RMX 2450 is no cream puff. The 2-rackspace unit weighs in at
44.5 pounds, so you may need help loading it into your rack. It
includes front and back mounts, and unless you happen to be placing
the amp in the bottom two spaces, you'll definitely want to use
both mounts. A peek under the hood revealed a large toroidal power
transformer and a wind-tunnel cooler for the power transistors. An
exceptionally quiet variable-speed fan adjusts to changes in
temperature, increasing speed as needed. The fan pushes air from
the rear of the amp to the front, which reduces the amount of heat
transferred to any other gear mounted in the same rack.
This fan arrangement is fine if the RMX 2450 is the only amp in
your rack, but if you use more than one and the second amp pulls
air from the front to the rear, you could end up with an air
recycling problem in which each amplifier sucks up the other's
exhaust. Of course, you always want to be certain any power
amplifier is adequately ventilated, so bear this in mind any time
you're positioning the RMX 2450 in a rack next to other gear.
PLUG ME IN, JACK
The RMX 2450 has the full complement of inputs and outputs you
would expect to find on a professional power amplifier. It has
three types of inputs: balanced XLR connectors, balanced
¼-inch TRS jacks, and a barrier strip. The balanced inputs
reduce hum on long cable runs and fight those bothersome ground
loops. A very useful 10-position filter and input switch defines
the amplifier characteristics. You can enable a clipping limiter,
insert a 30 Hz or 50 Hz low-frequency cut filter, or choose
bridge-mono output mode. The parallel input allows you to plug in a
single XLR or ¼-inch TRS plug and have both sides of the
amplifier patched to it without any Y-cables. Moreover, the switch
settings are silk-screened right onto the back of the amplifier.
While I'm on the gig, I simply hate having to pull out a reference
manual for something as simple as bridging an amp — so thank
you, QSC!
Outputs are on both high-quality binding posts (aka banana
jacks) and two types of Neutrik NL4-MD Speakon jacks. The binding
posts can handle even the thickest-gauge speaker wire, and the
Speakon jacks give you a quick twist-and-go connection that can
pass either mono or stereo channels down a single cable. One
Speakon jack is wired for mono signals only, while another is wired
to pass two channels down four conductors. This is convenient for
an instant connection to both standard stereo and biamplified
speakers.
Each channel has separate controls, enabling you to use one side
of the amp for a subwoofer (with the low-frequency filters turned
off), and the other side to drive a full-range speaker system (with
the 50 Hz filter inserted). This isn't quite as handy as a true
subwoofer crossover at 100 or 125 Hz, but it does protect the
speakers from infrasonic excursions (inaudible sounds below 16 Hz
that listeners can only “feel”) — these can sap
headroom power and overheat the voice coils needlessly. Gain
controls and separate signal and clip lights for each channel are
also located on the front panel. The input controls are not
detented, however, making them more difficult to match than
necessary.
IN THE HOUSE
I used the RMX 2450 in one of my most critical live shows last
December: the winter solstice concert at Meyerhoff Symphony Hall in
Baltimore. The act was Helicon, a high-caliber 3-piece Celtic and
world music group. The room, which seats 2,700 listeners, has a
large speaker cluster over the stage to cover the balcony seating,
as well as a set of Eastern Acoustic Works (EAW) apron speakers on
the downstage lip.
On the edges, I put up my Community speaker system, powered by
the RMX 2450, and patched in to the house cluster. Meyerhoff
Symphony Hall is a serious listening room, and the audience has
come to expect a lot from the winter solstice concert, so I always
pull out all the stops for this particular group of listeners.
The amp worked just as it was supposed to. If I had to sum up
the RMX 2450's sound in a word, it would be transparent. A really
great power amp shouldn't color the sound at all (unless it's in a
state of overload, and even then it shouldn't add too many clipping
artifacts or sound strained). Without a single compressor or
limiter patched in anywhere, stunning overall sound emanated from
my system, with gorgeous details on the hammered dulcimer strings
and a very solid bottom end for piano. I never heard any hint of
sonic strain, even when I was smacking the clip lights with
percussion peaks.
I also used the RMX 2450 for a loud rock band in a small club
the following week. The amp took a beating and never overheated,
acted up, or otherwise demanded attention. That's exactly what you
should expect from a great power amplifier.
All in all, I found the RMX 2450 a solidly built and versatile
piece of gear, equally at home in small or large venues —
very impressive indeed.
Mike Sokol is an audio engineer and musician who's been on both
sides of the microphone for more than 30 years. His first attempts
at live sound in the ’70s resembled the TV series Junkyard
Wars, but it's gotten a little better since then. Check out his Web
site at www.modernrecording.com for old and new
stuff.
RMX 2450 SPECS
Inputs (2) XLR, (2) ¼" TRS phone, and barrier strip
Outputs (2) binding posts, (4) NL4-MD Speakon jacks
Power 475W @ 8, 750W @ 4, and 1,200W @ 2 (per channel)
Frequency Range 20 Hz-20 kHz(+0/-1 dB, -3 dB @ 5 Hz and 50
kHz)
Noise 100 dB below rated output
Input Level 1.15V (+3.4 dBu) for full output
Dimensions 19" (W) × 3.5" (H) × 15.9" (D)
Weight 44.5 lbs.
PRODUCT SUMMARY
QSC
RMX 2450 Power Amplifier
$899
Overall Rating (1 through 5): 4
PROS: Extremely flexible I/O. Variable-speed fan is very quiet
until it's really needed. Plenty of power and headroom in a
2-rackspace chassis. Sounds like a high-grade hi-fi amp.
CONS: Nondetented input-level controls. Front-exhaust cooling fan
could cause air circulation problems when racked with rear-exhaust
amps. Could use a 100 Hz filter setting for subwoofers.
Contact:
QSC Audio Products tel. (800) 854-4079
e-mail info@qscaudio.com Web
www.qscaudio.com
