Martin Audio ASX User Manual page 11

A transducer that would minimise the voice coil resistance, maximise the Bl "force factor", or
that would present a more reactive load, would enable a significant increase in the
conversion efficiency.
In the practical embodiment of the IPAL principle in the ASX, DSP controlled, active
feedback topology "emulates" an ideal virtual "target" transducer to maximise efficiency and
maintain linearity at maximum excursion. Distortion is reduced by up to 20dB and power
compression virtually eliminated.
The IPAL system in the ASX comprises a dedicated Class D amplifier module, a DSP
system, a 21" (530mm) transducer unlike any other and a differential pressure sensor.
The drive unit
A neodymium motor system of immense proportions, coupled with a voice coil impedance of
less than one ohm enables the drive unit to generate an unprecedented force upon the air
load presented by the enclosure. This ability dominates the rest of the driver's electro-
acoustic parameters thus creating the "virtual transducer".
By adjusting the processing in the control loop, fixed parameters such as moving mass,
resonant frequency and even cone area can be "virtually" adjusted and optimised.
To handle the unprecedented forces and resultant air pressures requires an extremely
strong cone material. Made from a mix of cellulose and carbon fibres, the cone has
excellent strength when in tension and compression – unlike woven aramid fibre cones,
whose compressive strength is much lower than their tensile capabilities.
Amplification and DSP
The efficient Class D amplifier topology in the ASX is capable of delivering a peak power of
8.5kW and dramatically reduces the amount of energy dissipated as heat, as well as being
much smaller and lighter than other amplifier topologies.
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