The Cool Subwoofer

The Cool Subwoofer: Better Voice Coil Cooling = Better Music

A major factor in improved car subwoofer design is the development of the voice coil cooling processes. The sub 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?MTX 95 Series Car Subwoofer Exploded View

A voice coil (VC) is the coil of wire attached to the base of the speaker cone. When the amplifier oscillates the signal to the voice coil, an electromagnetic field is generated around the VC that reacts quickly in repulsion or attraction with the stable magnetic field of the large permanent magnet to drive the cone back and forth in proportion to the amplifier signal. The closer the voice coil follows this signal, the more accurate the reproduction of the original music.

Why is voice coil cooling important?

Ideally, the voice coil transfer of electric energy to acoustic energy would be 100%. But in reality, only about 1-2% of the amplifier current energy gets transferred and the rest goes to creating heat. So for loud, extended car subwoofer play, excessive heat will occur.  Excessive heat can alter the performance or even damage the voice coil, so proper subwoofer designs built to remove voice coil heat are imperative to getting long-lasting, accurate bass performance especially at high volume.

Speaker parts including the voice coil must be designed to be low in mass to avoid inertial dampening on quick transients in the music. This makes the VC delicate, so too much power passing through the coil can cause overheating. A subwoofer is specified to handle a maximum RMS power (wattage). If an amplifier rated for a larger wattage is connected and driven too hard, damage to the voice coil can occur. But even at matched amplifier ratings, it is important to properly set the gain of the amplifier to deliver only the maximum ‘clean’ signal and not be overdriven. (Besides possible heat damage, poor gain adjustment can cause signal clipping which results in music distortion)

Voice coil heat above 232 degrees Celsius are extreme and can cause damage from the degradation of the adhesive systems. In addition, VC resistance is also affected by heat, so undue distortion can be introduced.

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, the clipping that occurs causes less movement per energy level, which contributes to excessive heat. (Note this is typically a problem with amps rated the same or more than the sub)

Always remember that amplifier output is not intended to go to the top of your volume control or even three quarters. And depending on the gain setting, the tone adjustments (bass, equalizer, etc) can skew the subwoofer amplifier output up at the same volume setting on the knob.

Choosing the right subwoofer

So you have seen how car subwoofer voice coil cooling is important to keep distortion to a minimum for clear, accurate sounding music and to prevent damage to the speaker. The louder you play your music, the more important it becomes to choose a sub that is rated for higher power, and choose an amp with average (RMS) output that is properly matched to the sub rating as well as tune the gain for proper performance. And the longer you expect to play music at loud volumes the more the cooling must be accomplished effectively.

So if you are going to crank up the tunes for a long cruise party, choose a high quality subwoofer with superior voice coil cooling features that can handle the load. You will be rewarded with crisp, clear sound that lasts for years.

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