Technology & Engineering

Aerated Polypropylene Cone Technology

Only the best materials will produce the best sounds.

Sound is made by a rapidly moving membrane, which produces sonic vibrations that are then mirrored by the membranes in your ear (your eardrums). In a loudspeaker, that membrane is the driver cone. The driver cone moves back and forth on a pole piece, taking up -and-down instructions from a magnet-driven motor.

To maximize efficiency, that motor deserves a cone made of material that is best suited for accurate sound reproduction. It should be something stiff (to better generate accurate vibrations) and yet lightweight (to move quickly in response to the motor). Cone materials can be anything from coffee filter-like paper, to food storage container lid-type plastic. Remember the old tin cans connected by string? The tin bottom of the can was your membrane.

In the search for audio accuracy, energy efficiency, and instant response, Polk engineers have spent years testing materials that might improve the performance of the standard driver cone. They took a major step forward when Polk joined with Johns Hopkins University to perform exclusive laser interferometer research on possible cone materials. This research allowed our engineers to see material responses on a microscopic level for the very first time, resulting in a slew of improvements in speaker technology.

One of the coolest technologies to come from our laser interferometry research is aerated polypropylene.

Finding the Best Balance of Stiffness, Damping and Mass.

Poly Cone Foam Crosssection Polypropylene is a superb material. It’s stiff, and when it’s formed into the complex, slightly concave shape of a speaker cone it retains that delicate shape despite the most intense twisting and bumping. Our laser interferometry research showed that polypropylene had a very low distortion rate. But, polypropylene is also relatively heavy, which makes it inefficient for accurate response in a speaker cone.

So, Polk engineers puffed up the polypropylene with a super secret ingredient, air. Injected air formed a honeycomb structure in the polypropylene. (You can see this in the scanning electron microscope cross-section, at right.) Suddenly, the heavy material was lightweight. Yet, it retained all its great cone qualities! It was stiff and durable, but lightweight and efficient.

Lightweight aerated polypropylene cone materials deliver maximum stiffness and efficiency, with minimum cone resonances. As an integral part of Polk’s Dynamic Balance® material & construction technology, aerated polypropylene cones ensure an articulate response over a wide dynamic range, for superb accuracy and lifelike realism.

This article was last modified on Mar 26, 2013

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