Apogee APL-220, Руководство пользователя

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A clipping LED indicator is located on the rear panel. This LED will illuminate
when the speaker is several dB into limiting and indicates maximum operat-
ing level has been reached. It is not uncommon to see these LEDs illuminate
regularly, such as on downbeats and crescendos.
If the LEDs appear to be "on" more than "off " (i.e., if they are continuously
flashing or glowing at a steady state), the loudspeaker system is being pushed
too hard for its size and power output capability. To correct this, reduce the
drive level to the speaker system, or install additional speakers to achieve the
SPL (Sound Pressure Level) required for the application.
(4) A Word About Limiters
Properly designed protective limiters can do wonders to help prevent driver
damage and extend normal driver life, but they are by no means a panacea.
Apogee limiters do not exhibit “brick-wall” characteristics because such limiters
seriously degrade sound quality. Apogee’s intelligently engineered limiter circuits
provide an excellent measure of protection, while maintaining sonic purity.
Apogee's limiter circuits are capable of effectively reducing program levels
that would otherwise damage the system’s drivers. This takes place with little
or no loss of sonic quality or dynamic range, because the circuits are designed
so that they only engage when driver non-linearity or driver damage would
otherwise occur. However, when a limiter is pushed well past its threshold of
engagement to the point where it is continually “in circuit”, by nature it
increases the duty-cycle of the program material. This happens because, as the
limiter decreases peak amplitudes, RMS values increase, causing the drivers to
heat beyond normal. Additional circuits could be employed to reduce levels
and “clamp” the output of the system, but such circuits would represent a
high level of intervention and be very audible in their action. The proper solu-
tion is for the operator to recognize that the system is being pushed past its
capabilities and either reduce the operating level or add additional speaker
systems to provide the desired Sound Pressure Level (SPL).
(5) High-Pass Filter (HPF) Switch
The APL-220, -500 , and -800 are equipped with a switchable High-Pass Filter.
The filter is of the
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2 dB/octave type with a corner frequency of 80 Hz. The
High-Pass Switch is intended to be used when the speaker system is not
required to produce full-range output, such as in downfill, front fill, and other
band-limited applications. By using the High-Pass Filter Switch, the speaker
system can be driven approximately 6 dB harder before LF peak and LF RMS
limiters are engaged. The switch is located on the rear panel below the Input
XLR connector. It is recessed with only a small portion accessible, so that it
cannot easily be changed inadvertently.
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