JBL Professional MXP1200 - Manual (Page 4)

PROTECTION FOR YOUR
LOUDSPEAKERS
TRANSDUCER EXCURSION (PEAK)
Xd mm
MPX Series amplifiers provide the protection
of a steep 30 Hz high-pass filter that keeps
inaudible, but damaging, infrasonic (also
called subsonic) frequencies from reaching
your loudspeakers. Today's vented speaker
systems can be damaged by signals below their
resonant port tunings, which are typically
around 30 Hz or 40 Hz. These low
frequencies can cause excursion (cone travel)
beyond the loudspeaker’s safe capability.
Because these infrasonic signals can be
induced into your system anywhere along the
signal path, filtering incorporated in line level
equipment does not protect from signals
induced later in the chain. The MPX Series
provides the safety of filtering these potentially
damaging signals just before they get amplified
and sent to your loudspeakers.
The high-pass filter may be defeated for
applications such as driving digital cinema
subwoofers, where energy below 30 Hz is
required, and where the speakers are
specifically designed to safely accept this
spectral content.
40
35
30
25
20
15
10
5
0
WITHOUT FILTER
WITH FILTER
Other loudspeaker protection features include
relays to protect against DC offset and a
muting circuit to eliminate turn-on surges
when powering up. In addition, the largest
model, the MPX1200, provides clip limiting.
MPX Series incorporate professional amplifier
self-protection features, including full
protection for short circuit, open circuit,
ultrasonic and RF conditions, as well as
current limiting and thermal muting.
STABLE WITH ANY LOAD
ACOUSTIC ON AXIS RESPONSE: SPL, PHASE
100
95
90
85
80
75
70
65
60
dB
WITHOUT FILTER
You never know what load you’re going to
have to drive on any particular night. Maybe
one night some of your equipment racks don’t
show up at the venue . . . or you find you
have to add a few extra speakers to cover an
odd-shaped room. Perhaps a speaker cable
develops an intermittent short that could cause
other amplifiers to fail. With your MPX
amplifier, you can drive into any impedance
load, even below 2 ohms, safely and reliably.
Whether you use an amplifier from JBL or
from another company, we highly recommend
operating nominal load impedances of 4 ohms
or higher to obtain optimum performance
from your sound system. Unrelated to the
capabilities of the power amp itself, sound
systems utilizing very low load impedances
incur greater line losses through the speaker
cabling, higher distortion, and deteriorated
speaker damping (“flubby” lows).
While it’s not a good idea to run low
impedances, it’s comforting to know that your
MPX amp can take it if you ever find yourself
in a situation where you have to occasionally
run a low impedance load. To help out in
these situations, the extra cooling capability
means MPX’s will run longer continuously into
low impedances before overheating than most
other amplifiers.
AGENCY APPROVALS FOR SAFETY
AND PERFORMANCE
As a measure of safety you will be pleased to
know that MPX Series amplifiers are UL listed
as well as approved by the CSA and TUV safety
agencies.
An added plus, MPX amplifiers are approved
by Lucasfilm Ltd. ® for use in THX ® cinema
system installations*. This approval ensures
that the product has met or exceeded stringent
performance and power output requirements,
as determined by the experts at Lucasfilm
® .
POWER TO SPARE
MPX Series power amplifiers deliver
continuous power capability that accurately
matches the power handling capabilities of
most JBL professional loudspeaker systems.
In addition, MPX Series amplifiers feature a
high dynamic headroom capability of nearly 3
dB, for clear and powerful transients. This
reduces the incidence of amp clipping, which
is the most frequent cause of compression
driver failure.
WITH FILTER
THE RIGHT AMPS FOR
WORKING PROFESSIONALS
The MPX Series power amplifiers include the
features that working professionals need most,
so you get the best performance from your
professional sound system. As a working
professional, your amplifiers must meet the
challenges of today’s demanding audio
environment . . . MPX Series fits the bill.
*
THX is a registered trademark of Lucasfilm, Ltd.
10 20 30 40 50 70 100 Hz
FREQUENCY
FIGURE 1
TRANSDUCER EXCURSION
This illustration explains the protective action of the
3OHz, 18 dB per octave high-pass filter which, when
engaged, effectively limits low frequency transducer cone
excursion to within a safe range. The dotted line
indicates a damage threshold based on cone travel
(excursion). Note bow easily this threshold can be
reached and exceeded at infrasonic (subsonic)
frequencies with no filter protection. With the filter
engaged, you have substantially greater protection from
cone “over excursion” at these frequencies.
10 20 30 40 50 70 100
FREQUENCY
Hz
FIGURE 2
ACOUSTIC ON-AXIS RESPONSE
With the filter engaged, low frequency response is
smoothly contoured to deliver balanced output while
eliminating only the unusable and potentially dangerous
infrasonic energy.