ALUMINIUM CHASSIS - POLYPROPYLENE CONE Vented cast aluminium chassis for optimum strength and low compression. Unique mineral filled polypropylene cone material, made in-house. Soft low damping rubber surround for improved transient response. Non-conducting fibre glass CCAW voice coil former and extended copper sleeve on pole piece for low inductance and low distortion. Long life silver lead wires. Vented pole piece for reduced compression.