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Motional Feedback (MFB)
C 80 SUB features a Motional Feedback circuit. When a large woofer has been
abruptly driven by a strong sonic impulse such as an explosion or a timpani,
the woofer continues moving after the impulse stops. The MFB circuit com-
pares the impulse to be reproduced with the actual movement of the woofer.
If the woofer moves unnaturally in relation to the input signal, the MFB circuit
corrects the error before it becomes audible. Furthermore, the MFB makes it
possible to equalize the subwoofer to go deeper without losing any precision.
The result is incredibly accurate, deep bass, full of punch and dynamics.
Motional Feedback (MFB)
0
Impulse response [V]
Time - msec.
Without MFB With MFB
Boundary Gain Compensation
The Boundary Gain Compensation lter in C 80 SUB compensates for the
room inuence at low frequencies, as any room amplies the lowest frequen-
cies. The magnitude of the room’s amplication depends on the room size
and where the sub is positioned in the room – normally it increases the closer
the sub get to a wall. This can result in too high a bass level from approx.
60Hz and increasing downwards – in the range between 20 - 30Hz it peaks
up to 5 - 10dB in an average room!
At rst this could sound really impressive, but the sound quickly begins to
sound ‘boomy’, especially when listening to music, and rather annoying. So
the Boundary Gain Compensation ensures a very linear in-room bass response
and gives you more exibility when it comes to placement and choosing your
favourite listening position.
Boundary Gain Compensation
10.0
SPL/Volts [0.33 oct]
100.0
O On
Active Impedance Control (AIC)
All C 80 mid/woofers feature Active Impedance Control (AIC), an innovative
extension of existing techniques to reduce distortion in electrodynamic loud-
speaker drivers.
The AIC makes the impedance more linear in the mid and high frequency
range. AIC also increases the sensitivity and total SPL in the upper range of
the driver.
30
25
20
15
10
5
0
200 500
Impedance [Ohm]
1k 2k
Frequenzy ]Hz]
2k 10k 20k
driver with AIC driver without AIC
AIC - Active Impedance Control:
The eect of AIC is a clearer midrange with a markedly reduced ‘roughness’, es-
pecially noticeable on vocal reproduction. In gures, this amounts to a reduc-
tion of third-order harmonic distortion of around 6dB (ie a 50% reduction).
-35
-40
-45
-50
-55
-60
-65
200 500
[dB]
1k 2k
Frequenzy ]Hz]
driver with AIC driver without AIC
Harmonic distortion
When a voice coil is moving in and out of a magnet gap, it changes induc-
tion. When the coil moves inward, the induction increases and vice versa.
This causes the current from the amplier to be modulated, creating very
audible distortion.
Furthermore the current owing in the voice coil modulates the magnetiza-
tion of the magnet assembly which also causes distortion of the current.
By using an extra coil, placed inside the voice coil with opposite polarity to
the voice-coil winding, the inductance variation and the ux modulation can
be signicantly counteracted.
Compared to the conventional conductive rings in a magnet system AIC has
the advantage that it is signicantly better at higher frequencies i.e. in the
midrange (on voices) where distortion is most audible to the human ear.
Jamo Tech platforms
Frequenzy ]Hz]
Jamo C 80 page 07