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15 : 3.Thiele/Small parameters
The Thiele/Small parameters are electromechanical
parameters that define the performance of a loudspeaker
driver. T/S parameters are provided by driver manufacturers.
In order to setup the system, you are asked to enter the
following T/S parameters:
f Fs: loudspeaker resonant frequency in free air (Hz);
f
f Qes: electrical loudspeaker damping at resonance
f
(unitless);
f Qms: mechanical loudspeaker damping at resonance
f
(unitless);
f Vas: volume of air with the same acoustic compliance of
f
the driver suspension in free air (cubic meters or liters);
f Re: electrical resistance of voice coil (Ω);
f
f Sd: effective projected surface area of the driver dia-
f
phragm (square meters).
f Cms: suspension compliance (m/N)
f
f Mms: effective moving mass combining cone, coil, all
f
moving parts and the acoustic load by the air in con-
tact with the loudspeaker cone (kg);
f Rms: suspension and all moving parts losses or
f
damping (mechanical ohm);
f Bl: force factor, i.e. strength of the magnetic field times
f
the length of the wire forming the voice coil (T·m or N/A).
Furthermore, the system takes into account the folloging data:
f Sound speed: speed of sound (meter/second)
f
f Ro medium density: air's medium density (kg/m3)
f
15 : 3.1. Calculated parameters
The Power Control Manager derives the following data:
f Qts: total loudspeaker damping at resonance combin-
f
ing electric and mechanical effect (unitless):
Qms·Qes
Qts =
Qms+Qes
f Cmes: electrical capacitive equivalent of the moving
f
mass Mm (farad)*;
f Lces: electrical inductive equivalent of the suspension
f
compliance Cm (henry);
f Ref eff. no: loudspeaker free air standard reference
f
efficiency (unitless);
( )
Ro
(Bl)
Sd
2
no =
2�c
Re
Mms
f Ref eff. no%: same as Ref eff. no in percentage;
f
f Ref SPL: reference sound pressure level (dB):
f
Ref SPL = 112 + 10 log(no).
18 | IpalMod | User guide
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15 : 4.Advanced parameters
Advanced parameters are common to both Virtual
speaker and Pressure model modes. Before accessing the
Advanced parameters window by clicking on the Advanced
button, a dialog box asking a password appears.
The Advanced parameters default password is
filippo
This extra step in necessary to ensure that system
parameters are not changed by mistake as incorrectly set
values can permanently damage the system.
As an added precaution, when the user tries to assign a
parameter value outside the range of acceptable values, the
text box is highlighted in red and the parameter automati-
cally set below the safety threshold.
FIGURE 25: Advanced parameters.
15 : 4.1. DSP setting parameters
The Zero Latency DSP implements a number of limiters
that can be activated and customized by the user:
Current limiter
Set a threshold limit and the attack/release time for the
average (rms) output current.
Current clamp
The Current Clamp is a faster acting current limiter.
Current Clamp is meant to limit spikes of current, effectively
protecting the output stage and the connected loudspeaker
from dangerous high peak current: this is different respect
the short circuit protection that works by sensing decreas-
ing rails values.
The current threshold value does not indicate the
maximum output current, but the current level at which the
limiter will start sensing spikes of current. Output current
level can exceeds the clamp threshold considerably due to
the internal limiter design.
Brownout
Brownout is an even faster acting output peak power
limiter, and works on a different principle than all other
limiters.
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