Klippel R&D System
KCS Monitor Tutorial
9
1.
Transducer produces Impulsive Distortion
Xmax
is determined during KCS-ID using an imported target excursion value and using an IDR
(
Impulsive Distortion Ratio
) measurement. It can happen that the IDR limit in KCS-ID was set
too low or was deactivated. In addition, it is not very sensitive for certain irregular distortion
such as air flow noise.
If audible impulsive or other irregular distortion (e.g. Rub&Buzz) is produced by the
transducer during evaluation (subjective and objective tests), reducing the
Excursion Limit
can increase sound quality.
2.
Amplifier is not sufficient
If the maximum excursion
Xmax
set by KCS-ID/KCS Server cannot be reached with the used
amplifier due to insufficient peak voltage, the voltage limiter will activate frequently to avoid
amplifier clipping.
As a limiter can degrade the perceived sound quality due to its inherent nonlinear behavior,
it can be beneficial to limit
Xmax
. Especially if a significant bass boost is applied (maximum
gain > 10 dB) so that a major part of the voltage needed to reproduce broadband signals is
used at low frequencies, reduce the
Excursion Limit
to lower peak voltage requirements.
Good indications showing that the amplifier is not sufficient for achieving
Xmax
is that
‘KCS Output Limiter active’
in the
State
window pops up regularly
u out peak
in the
Voltage and Current
window is regularly reaching the
U limit
value
displacement is always significantly (>10 %) below the protection limit
Xprot
indicated by the bold red lines in the
Displacement
window, even when the amplifier
voltage is at its limits
Thermal Protection
A conservative default limit is set automatically on the KCS Server. Anyway, make sure that it is
below the maximum rating of your transducer. Note that the limit value is a temperature increase in
the unit
Kelvin,
referenced to the temperature during the KCS-ID measurement. It should be
adjusted if better values are provided by the transducer manufacturer. Anyhow, choose a
conservative value as the voice coil heats up nonhomogeneous, but the thermal protection relies on
an average coil temperature.
Output Voltage Limiter
Default values for the limiter are set automatically on the KCS Server if the maximum voltage of the
power amplifier is known, for instance the KA3’s AMP card, the APE evaluation board and the NAD
platform. In this case usually the limiter setup parameters do not have to be changed. However, in
some cases manual adjustments as described in the passages below might increase the system’s
performance:
If a strong bass boost is performed (>12 dB maximum gain), the major part of the total voltage is
used at low frequencies for broad-band signals. Then
CU Deactivation
can be set to a high negative
value (-6 … -12 dB) and the limiter will mainly attenuate low frequencies. If no significant bass boost
is performed (<6 dB maximum alignment gain),
CU Deactivation
should be set to approx. -3 dB.
The audio system should not be used with the voltage limiter activating all the time as this might
degrade audio quality. For improved sound quality it is better to reduce peak voltage requirements,
for instance by
