MACKIE HR824 - Manual (Page 11)

11
The HR824 is a bass reflex 6th-order system.
Rather than use ports, the vent takes the form
of a passive radiator, a mass-loaded flat piston
coupled to the air trapped within the enclo-
sure. You can’t see the passive radiator because
it is located at the rear of the cabinet, behind
the power amplifier assembly.
• Simple ports or ducts must have sufficient
surface area to prevent the velocity of the
air within them from exceeding 5% of the
speed of sound, which keeps the vent from
becoming audible (breathing and wheezing
sounds) at high signal levels.
• This requirement for sufficient surface area
creates a design problem when using ports —
finding enough space in the enclosure for
them to fit.
The passive radiator replaces the port found
on most speaker systems. It offers several ad-
vantages to simple porting:
• One primary advantage is that a passive
radiator can reproduce low frequencies
with lower distortion and at a higher sound
pressure level (SPL) than a simple port or
duct.
• Our unique passive radiator design uses a
diaphragm made with a composite honey-
comb material providing exceptional
stiffness to the radiating surface.
• The elliptical shape of the passive radiator
takes up nearly the entire surface area
available on the rear of the enclosure,
allowing the passive radiator to move more
air than a port.
input signal level of –45 dBu (minimum)
activates the auto-on function. A silent
period greater than five minutes activates
the auto-off function. The red
PWR LED
on the front panel reflects the state of the
amplifiers.
MAINS INPUT
Connect the power cord to this IEC socket, and
plug the other end into your AC outlet.
• When the
POWER MODE switch is in
the ON position, and the power switch
is in the ON position, applying AC power
activates the muting circuit for about four
seconds while the power supply and
internal circuitry stabilize.
PASSIVE RADIATOR
When you mount a loudspeaker in a box,
there are two things that you can do with the
radiation from the rear of the cone: use it to
enhance the low-frequency performance of the
speaker system (bass reflex system) or soak it
up (acoustic suspension system).
• A bass reflex system uses the rear radiation
to extend the low-frequency response. Most
systems provide holes (ports) in the front
or back of the cabinet to release the rear
wave. Sometimes the holes have tubes
(ducts) in them. The dimensions of the
holes and the volume of the cabinet work
with the characteristics of the woofer to
produce low-frequency extension. These
systems are characterized by good low-
frequency performance down to the –3 dB
frequency set by the design. Below this
frequency, the frequency response falls at
24 dB/octave or more.
Tweeter
Woofer
Passive Radiator