Starting and stopping

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Starting and stopping

Ever wonder why loudspeaker designers get so excited about woofer cone materials like Kevlar, aluminum, paper, sandwich cones of carbon fiber, and other materials?*

Their excitement comes from understanding the challenge of making an air piston (which is what a speaker driver is) that can start and stop in perfect synch with the instructions from your power amplifier.

To accomplish that feat one would prefer a cone (the piston part) that had zero mass (so it could start and stop without offering any resistance) and yet was stiff and strong enough not to deform when moving (its mass and shape determine its strength). Two impossible requirements: light enough to move yet heavy enough not to get deformed.

In engineering speak the designer needs to worry about mechanical compliance.

The mechanical compliance of a woofer is determined by its mass and suspension (surround and spider). The more massive a woofer is, the more difficult it is to move (and stop moving), and the less compliant it is. A less compliant woofer will have a slower response and will be less sensitive to high-frequency signals (transients), but will have a greater ability to produce low-frequency sounds with high output levels.

Taken to extremes, a massive heavy woofer cone (like one machined out of an aluminum billet) will not deform but at the cost of not being able to start and stop quickly (distortion from a lack of transient speed and overhang). Or the opposite: so low in mass that it wrinkles and deforms with the smallest blush of power applied.

The next time you listen to your speakers you might want to give a tip of the hat to all the engineering that goes into making bass.

Woof!

*(The new aspen FR20, for example, utilizes an exotic low-mass PMI foam core with non-woven carbon fiber skins on each side to accomplish its impossible task and it works great!)

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Paul McGowan

Founder & CEO

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