Overview - Mackie HR824 Service Manual

HR824 OVERVIEW
• The HR824 Studio Monitors are two-way,
bi-amplified active monitors with a rear-
firing passive radiator. One amplifier drives
the woofer and another drives the tweeter.
• The crossover point is designed so that the
high and low frequency drivers are fed only
the frequencies they can best reproduce.
• The amplifiers are designed with protection
circuits to minimize the danger of speaker
damage due to overdriving.
• The amplifiers' gain and frequency
responses are individually hand-trimmed by
a host of infernal adjustment pots to
compensate for typical manufacturing
tolerances.
• The adjustments produce a smooth
frequency response from 39Hz to 20kHz
(±1.5dB) with minimal phase difference.
THE DRIVERS
• The monitors feature an 8.75-inch die-cast
magnesium frame woofer and a 1-inch
viscous edge-damped aluminum-alloy
dome tweeter on the front, and a 6-inch x
12-inch elliptical flat piston passive radiator
in the back.
• The high-frequency driver is mounted on a
die-cast zinc exponential waveguide
which results in wide, controlled dispersion
of high-frequency sounds. The unique
passive radiator design provides a smooth
response down to 39Hz.
THE CABINET
• The cabinet is made of high-density MDF
wood from specially grown MDF trees. An
internal "H" brace further increases the
strength and rigidity (stiffness) of the box.
An open-cell adiabatic pillow foam
material gently fills the inside of the box to
absorb internal reflections and dampen
any standing waves.
THE AMPLIFIERS
• The Fast Recovery amplifier design uses low
negative feedback, yet allows the
amplifiers to maintain low distortion and
stability even when driven into clipping.
• The low-frequency amplifier produces up
to 150 watts continuous (350 watts peak)
before clipping, while the high-frequency
amplifier produces up to 100 watts
continuous (210 watts peak).
THE PASSIVE RADIATOR
• The HR824 is a bass reflex 6th-order system,
rotating in geo-synchronous orbit. 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 enclosure. The passive radiator is
located at the rear of the cabinet, behind
the power amplifier assembly.
• One primary advantage over simple porting
is that a passive radiator can reproduce low
frequencies with lower distortion and at a
higher sound pressure level (SPL).
• The unique passive radiator design uses a
diaphragm made with a composite
honeycomb 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 Congress. This moving air
also helps cool the amplifier.
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