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DPA Series — DPA80/DPA100 Operating Instructions
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Setting Accurate Limiter Thresholds — Program Limiter
Introduction
The limiters built into your amplifier are intended to be used for loudspeaker driver
protection, as opposed to amplifier protection. The amplifier has additional limiters which
can adapt automatically to both temperature and incoming mains conditions to stay
operational and playing music for as long as possible. The following section describes how to
set up the units’ limiters to provide exceptional protection against driver overheating and
cone over-excursion. Most speaker systems are given a power rating in Watts RMS. This is
the maximum continuous power that the system will handle and often appears very
conservative. In reality, as music program is far from continuous in nature, the peak power of
the system is much higher — up to ten times the continuous figure. Any limiter, which is to
protect the driver from damage, must be able to fulfil the following tasks:
-
Have an attack time which is calculated to allow transients through but keep the RMS
level below the speaker manufacturers specification;
-
Have a release time which is sufficiently long to avoid the limiter itself modulating the
program;
-
Be intelligent enough to adjust the envelope of the limiter according to the frequency
content of the program material.
The RMS limiters are capable of performing all these tasks. The only parameter that the user
must set manually is the threshold, and it is crucial that this is done correctly.
