What does the overload protection circuitry do, how does it work?
When any speaker system is played loud for a long time the voice coil of the driver heats up. Eventually the voice coil may fuse and the driver will need replacement. The driver overload protection built into all GENELEC monitors is designed to protect the monitor drivers and is based on modeling the driver's thermal performance.
It is NOT a compressor, as the signal dynamics are not affected. Also, it is NOT a limiter, as the driver protection system turns down the whole signal input to the filter and amplifier stages. This driver protection system allows the use of over-amplification to improve signal dynamics whilst guaranteeing overall system reliability.
If the red OVL LED is permanently ON the driver protection system is operating and the amplifier may be clipping. The input signal to the amplifiers is automatically attenuated to allow the drivers to cool sufficiently before resuming normal operation. Turn down the input signal to the monitor so that this is not repeated.
If the red OVL LED flashes it indicates that the amplifier has clipped. Turn down the input signal to the monitor slightly to ensure that you are listening within the linear operation of the monitor.
Note: There is no red OVL LED on the models 8020B, 8030A, 8130A and the discontinued 1029A, 2029A, 2029B and 1030A. However the protection system operates in the same way to ensure long term reliability of the monitor.
Different source materials will cause different effects to be noticed. This is dependent on the crest factor (the ratio of peak level to rms level) and typical values are shown in the table below. It should be noted that all of this is highly frequency dependent and the values are a broad band indication only. Also note that crest factor is not the same as dynamic range which is the difference between the peak level and minimum level.
At one extreme, symphony music has a high crest factor due to the dynamic style of the music so the monitor amplifier will tend to clip before the protection operates. A flashing LED will be noticed at high output levels.
At the other extreme, modern music styles have a low crest factor due to the compression techniques used in the production stage and the style of the music itself. The driver protection system will tend to operate at high output levels before the amplifier stage even starts to clip.