20 | K Series | User guide
Octave
band (Hz)
Attack time
(ms)
Release time
(ms)
Atk/Rel ratio
63
45
720
x16
125
16
256
x16
250
8
128
x8
500
4
32
x8
1000
2
8
x4
> 1000
1
2
x2
TABLE 8: Attack and release times per octave bands.
Where
Re
is the nominal impedance of only one driver,
P
peak
is the peak power and
V
peak
is the peak output voltage.
A peak limiter, used with a very short attack time (i.e.,
with a very rapid onset), can also be useful in limiting the
maximum peak voltage in distributed constant voltage lines.
Powersoft designed the K Series limiters as protective
measures; therefore, they are not meant to “color” the
sounds such as dynamic compressors can do. With this in
mind, time constants for these limiters should be selected
so as to limit potentially harmful phenomena which persist
for no more than one or two periods of the related signal
bandwidth.
TABLE 8
gives a few examples of attack and release
times with respect to the frequency range of the signal to
be limited.
The peak limiter menu allows the user to define the fol-
lowing parameters:
f
f
Active
: toggles the power limiter’s on/off status;
f
f
Threshold (V
pk
)
: the peak voltage threshold at which
the gain begins to be reduced;
f
f
Attack
: the attack time, i.e. the response time of the
limiter intervention;
f
f
Release
: the decay time, i.e. the time constant after
which the limiter’s action is released and the gain re-
stored to the nominal value.
In order to avoid choking the exceptional dynamic range
offered by K Series amplifiers, the peak limiter is designed
to ignore signal peaks lasting less than the attack time pa-
rameter. Moreover, the limiter has an additional lookahead
buffer (0.5 ms) to soften clipping and minimize distortion,
effectively yielding superior sonic performance.
When tweaking the peak limiter’s levels, it is preferable
to first setup the time parameters, and then adjust the
threshold voltage. When editing the threshold value, the
display shows the gain reduction (GR) in dB enforced by
the limiter.
This information, together with the limiting voltage re-
ferred to the signal in the input amplifier stage (I) expressed
in dBu, is displayed in real time to allow monitoring of the
limiting actions as they are performed.
9 : 11.6.1. Peak Limiter
The peak limiter avoids potentially dangerous displace-
ments of the cone (an excursion larger that allowed). It acts
by reducing the amplifier gain in order to reduce the meas-
ured output peak voltage. To limit the dangers of dangerous
very fast transient signals, all limiters implement a look
ahead time of 0.5 ms.
As a rule of thumb, use the declared peak power or
twice the program power as a loudspeaker safe-zone out-
put power.
The peak limiter’s setting do not change with the num-
ber of parallel speakers connected to the amplifier, this is
because the same voltage is applied to all the components
in a parallel circuit. When deciding parameters for a peak
limiter of an amplifier with many loudspeakers connected to
it in parallel, the peak power to be taken into consideration
is that reaching only a single speaker.
You can refer to the following formulas:
f
f
Power limiter
: protects speakers against thermal
damage when excessive power is applied for extended
periods of time, resulting in overheating and, eventu-
ally, burning. Designers should be aware of the maxi-
mum long term power safely applicable to speakers
(AES power rating). An interesting approach to RMS
limiting is one that uses coil temperature control. A
complete knowledge of the driver’s limits allows to
keep the temperature level in a safe interval not only to
avoid damage but to maintain the speaker in a “linear”
zone that avoids power compression.
Active:ON
back
sel
Thresh.(Vpk):169
Attack(ms):10
CH1
FIGURE 30: Peak limiter settings.
Thresh.(Vpk)
ok
fast
-
+
169 Vpk
CH1
GR= 0.0dB I= 11.7dBu
FIGURE 31: Peak limiter: threshold
voltage and gain reduction.
P
peak
=
Re
V
2
peak
V
peak
= √
Re
∙
P
peak
