Mackie SRM 450 Service Manual - page 6
6
Overview
The SRM450 is an active two-way loudspeaker system capable of extremely high sound
pressure levels.
The Transducers
The SRM450 active monitors feature a 12” high-power low-frequency woofer and a 1.75”
titanium diaphragm high-output precision compression driver. This high
frequency driver is mounted on an acoustically non-resonant exponential waveguide,
providing a wide, controlled dispersion and precise reproduction of the critical upper
mid-range and high frequencies. The result is an unbelievably smooth off-axis response
that allows everyone in the audience to experience the same high-resolution audio no
matter where they are seated.
Each driver has been specifically designed by our engineers for optimum performance in
the lightweight high-strength cabinet.
FR Series Power Amplifiers
To power these beautiful things, each SRM450 includes two of our acclaimed FR Series
“Fast Recovery” power amplifiers. Our exclusive design uses low negative feedback, yet
allows the amplifiers to maintain low distortion and stability and to quickly recover when
driven into clipping.
The amplifiers include the following features:
•
The low-frequency amplifier produces up to 540 watts peak (300 continuous)
before clipping.
•
The high-frequency amplifier produces up to 150 watts peak (100 continuous)
before clipping.
•
Each amplifier has its own compressor circuit that acts when the input signal is large
enough to cause clipping, distortion and excessive voice coil heat. The compressor will
automatically decrease the input signal to a safe level. The compressor in the low-
frequency amp works independently from that in the high-frequency amp.
•
The low-frequency amp uses a servo feedback loop which senses the current flowing in
the woofer coil. This controls the low-frequency response and maintains low distortion at
high output levels.
•
The low-frequency amplifier also has a sweeping filter. This will automatically move the
low cut-off frequency up or down depending on the amplifier output. For example, if the
amplifier is below clipping, the low-frequency cut-off point is 55Hz. As it approaches
clipping, this shifts up smoothly to 120Hz, providing more power reserves and less
distortion before clipping. This happens quickly and continuously, protecting the amplifer
and the woofer and reducing any noticable distortion.
Warning: Although the amplifiers have these protection circuits, you must still make sure
the PEAK light is not blinking often or continuously. If it is, turn down your mixer faders, or
preamplifier gain, or turn down the SRM450 LEVEL control.