5.More About Dpc - powersoft IpalMod User Manual

This protection system quickly reduces the amplifier
gain when the rails voltage decrease quickly due to an ex-
cessive power draw from the load. Threshold voltage value
is the value beneath which the rail voltage must drop for the
limiter to begin acting. A threshold voltage value of 0 V, for
example, disables the limiter.
Power Limiter
Ensures that the real part of the average output power
does not exceeds the limits set by the user.
Overcurrent protection
The overcurrent protection acts similar to the current
clamp but faster. You can just set the threshold.
Excursion Limiter
The excursion limiter keeps the loudspeaker cone dis-
placement within a user defined range. The threshold cone
excursion is set in mm. The excursion limiter works through
a current loop, dynamically changing the value of a resist-
ance proportionally to the displacement of the cone with
respect to its resting position.
It is important to note that this position is estimated;
its accuracy depends on the precision of the connected
speaker physical parameters entered in the Physical
Speaker Parameters section in the advanced parameters
window (see below).
The Gain (ohm/cm) parameter sets the displacement/re-
sistance conversion factor, so as to regulate the intensity of
the limiting effect. For a given cone displacement, a higher
gain value yields a more severe limiting action. The release
time determines the time needed for the limiter to release
the cone.
Please note that the maximum cone excursion set in this
window only determines the cone displacement value that
activates the effect of the limiter; it does not represent the
maximum excursion the cone will display. The limiter's in-
ternal design allows for a certain margin between maximum
displacement threshold value and effective cone displace-
ment, the latter being potentially higher.
Thermal Limiter
The thermal limiter reduces the rail voltage by an amount
proportional to the difference between the threshold tem-
perature and the measured output stage temperature in
order to lower the module's temperature.
Lowering the rails voltage reduces output power which
in turn decreases ohmic heating of the output stage. The
scaling factor that governs the rails reduction as a func-
tion of this temperature difference is called KGain; it can
be entered by the user, although the default value (1000)
is already an empirical optimum. For a given temperature
difference, a higher KGain factor yields a more severe rails
voltage reduction.
Gate
The system is equipped with a gate output block in-
tended to improve the overall signal-to-noise ratio. The
gate reduces the output gain for small signals interpreted
as noise.
The hold time indicates how long the gain reduction oc-
curs after the output signal falls below the threshold. The
attenuation parameter indicates the amount by which the
output gain is decreased with respect to no attenuation.
Note that the system gain changes slowly and not abruptly
so the effect is unnoticeable.
Energy Save
In order to reduce power consumption when the amp is
not receiving any viable input signal, the IPAL system enters
an energy save operation mode. Lower energy consumption
is obtained lowering the rails voltage to the value entered in
the voltage threshold. The energy save mode is activated
only after no signal input is detected for more than the use
set activation time.
Advanced Parameters: Virtual Speaker RP (mohm)
The Virtual Speaker RP is a scaling factor used by the
pressure sensor. This depends on the specific pressure
sensor in use and must therefore be changed only if the
sensor is changed.
Advanced Parameters: Safe Mode Threshold
The Safe Mode provides a protection against critical
settings that may bring the system to instability or even to
damages.
When Safe Mode is active, the output power is limited by
the value enetered as Safe Mode Threshold.
Special care should be used while setting this value:
it must not be greater than the maximum power handling
capabilities of any part of the system.
Voltage RMS Limiter
Set a threshold limit and the attack/release time for the
average (rms) output voltage.
Voltage peak/Clip Limiter
Set a threshold limit and the attack/release time for the
peak output voltage.
Physical Speaker Parameters
Parameters in this section refer to the transducer
and are the same described in
parameters. Please note, however, that the parameters en-
tered in this window refer to the real loudspeaker whereas
those entered in the Virtual speaker mode may refer a virtual
transducer.

15 : 5.More about DPC

For more information about the IPAL and DPC tech-
nologies, please refer to: Blasizzo, Desii, Di Cola, Lastrucci,
Practical applications of a Closed Feedback Loop
Transducer system Equipped with Differential Pressure
Control, presented at the 131st AES Convention New York,
New York, October 20-23, 2011.
Setting the Differential Pressure Control | 19
Chapter 15 : 3.Thiele/Small