ALUMINIUM CHASSIS - POLYPROPYLENE CONE Vented cast aluminium chassis for optimum strength and low compression. Mineral filled strengthened Poly-cone made in-house. Soft low damping rubber surround for improved transient response. Non-conducting fibre glass voice coil former for minimum damping. Extended copper sleeve on pole piece for low inductance and low distortion. CCAW voice coil for reduced moving mass. Vented pole piece for reduced compression.