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In addition, it prevents over- and under pressure behind the dust cap when the

cone moves back and forth. The advantage is a more dynamic and precise sound

reproduction.

The aluminium Centre-Plug also has a cooling effect on the voice coil, providing

greater power handling capability and very importantly, a stable sound reproduc-

tion when playing loud.

The mid-woofers all feature lightweight 2-layer voice-coils in order to achieve maxi-

mum "attack" (the ability to start and stop precisely) and minimum distortion. These

acoustic properties are of utmost importance for optimum voice reproduction.

Active Impedance Control

All C 80 mid/woofers feature Active Impedance Control (AIC), an innovative exten-

sion of existing techniques to reduce distortion in electrodynamic loudspeaker

drivers.

When a voice coil is moving in and out of a magnet gap, it changes induction. When

the coil moves inward, the induction increases and vice versa. This causes the cur-

rent from the ampliﬁ er to be modulated, creating very audible distortion.

Furthermore the current ﬂ owing in the voice coil modulates the magnetization 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 ﬂ ux modulation can be signiﬁ -

cantly counteracted.

The effect of AIC is a clearer midrange with a markedly reduced in 'roughness' , es-

pecially noticeable on vocal reproduction. In ﬁ gures, this amounts to a reduction of

third-order harmonic distortion of around of 6dB (ie a 50% reduction).