A major factor in car subwoofer design is the development of voice coil cooling. The voice coil is the motor that drives your music's bass, and it takes the abuse of loud, long, or poorly tuned play when excessive heat builds beyond design limits.
What Is a Voice Coil?
A voice coil is the coil of wire attached to the base of the speaker cone. When the amplifier oscillates a signal to the voice coil, an electromagnetic field is generated around it that reacts quickly in repulsion or attraction with the stable magnetic field of the large permanent magnet. This drives the cone back and forth in proportion to the amplifier signal. The more closely the voice coil follows that signal, the more accurate the reproduction of the original music.
Why Voice Coil Cooling Matters
Ideally, the voice coil's transfer of electric energy to acoustic energy would be 100%. In reality, only about 1–2% of the amplifier's current energy gets converted to sound. The rest becomes heat.
For loud, extended car subwoofer play, excessive heat will occur. That heat can alter performance or damage the voice coil, so proper subwoofer designs built to remove heat are essential for long-lasting, accurate bass performance — especially at high volume.
Speaker parts including the voice coil must be designed with low mass to avoid inertial dampening on quick transients in the music. This makes the voice coil inherently delicate. Too much power passing through the coil causes overheating. Voice coil temperatures above 232 degrees Celsius can damage the adhesive systems that hold the coil together. Heat also increases voice coil resistance, which introduces distortion into the signal.
How Clipping Makes It Worse
A major cooling source for the voice coil — particularly in a vented enclosure — is the action of the subwoofer cone pumping air in and out around the voice coil gap. When an amplifier is overdriven and clips, the distorted signal it sends causes less cone movement per unit of energy. Less movement means less air pumping through the gap, which means less cooling. The result is more heat concentrated in the voice coil with less acoustic output — the worst possible combination.
An amplifier's output is not intended to run at the top of the volume control or even three quarters. And depending on the gain setting, tone adjustments like bass boost and EQ can increase the subwoofer amplifier's effective output without touching the volume knob.
Choosing and Setting Up Your System Correctly
A subwoofer is rated to handle a maximum RMS power. If a larger-rated amplifier is connected and driven too hard, damage to the voice coil can occur. Even at matched power ratings, it is important to properly set the amplifier gain to deliver only the maximum clean signal without overdriving it. Poor gain adjustment causes signal clipping, which results in both music distortion and excess heat.
If you plan to crank up the music for extended sessions, choose a subwoofer rated for higher power with superior voice coil cooling. Match it to an amplifier whose RMS output closely matches the sub's RMS rating, and tune the gain for proper clean performance. You will be rewarded with crisp, clear sound that lasts for years.
