Nova HDC 84, User Manual

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Limiters
The HDC48 includes three limiters in the output signal path. Please note that whilst the Limiters in
this product offer protection for amplifiers and drivers, they can never protect from all possible
scenarios, therefore NOVA is not responsible for any damage which might occur.
VX Limiter (Unique to NOVA)
This is a peak-detecting signal limiter. The VX Mode parameter determines the style of limiter. When
Virtual Crossover (VX) mode is off, the limiter is controlled in a conventional manner; the only
controls being Threshold and Overshoot.
The Overshoot limiter prevents the signal from exceeding threshold during the attack phase of the
main limiter by more than a predetermined amount. The optimal Overshoot setting is usually about
8dB. Lower Overshoot settings will sound progressively ‘harder’.
When VX mode is engaged, the user can choose the crossover point of a ‘virtual crossover’, which
incorporates two limiters per output so the user can individually limit the drivers in a passive 2-way
enclosure using individual thresholds, and optimised attack and release characteristics for each. The
Threshold of the second
‘Hi’ limiter is set relative to the threshold of the first ‘Lo’ limiter.
The effect of the VX threshold and split frequency on the Limiter curve can be seen in System
Engineer.
This Limiter introduces some delay. In non-VX mode, this delay will depend on the lowest high-pass
frequency used in the crossover filters in a given Drive Module. In VX mode, the delay is related to
the Split frequency. This delay will be applied to all of the outputs in a given Drive Module to keep
them in phase.
Also see Latency Delays
Tmax Thermal Limiter
The Thermal Limiter is intended to protect the driver against damage due to over-heating. It models
the temperature of the driver, and constrains the output signal level in order to keep the average
output power below a predetermined limit, applying attack and release characteristics to go some
way towards modelling the complex thermal circuit of a driver’s voice coil and magnet assembly.
Three parameters are available for adjustment:
Threshold
– the continuous RMS voltage which the driver should be able to withstand. This is
calibrated at the output of the amplifier. The Thermal Limiter can be defeated by setting the
Threshold to the maximum “Off” value.
Attack – The time-constant of the speed at which the driver heats up (in seconds).
Release – The time-constant of the speed at which the driver cools down (expressed as a multiple of
the Attack time).
Also see
Amplifier Gain
Xmax Excursion Limiter
The Excursion Limiter protects the driver against excessive linear movement of the cone and voice-
coil which could otherwise cause mechanical damage. Since this movement (excursion) is largely