Subwoofer Damage

“Blowing” a subwoofer refers to damage inside the woofer that causes unwanted noise or no sound at all. Damage can happen suddenly or slowly over time. Common causes of damage to woofers are clipping signals, over/under powering, and operating outside of the enclosure’s tuning. Each of these can cause specific damage to certain internal parts of the sub.

CLIPPING SIGNALS

A clipping signal can occur when an amplifier is pushed beyond its design specifications. Clipping is simply a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability. Driving an amplifier into clipping may cause it to output power over its power rating. The “peak” of the power waveform is “clipped” so it’s flat on top. The excess power from a clipping signal builds up as heat in the voice coils. As the temperature of the coil gets extremely hot, the coil adhesive melts, and the coils expand. Eventually they will detach from the former. If heat build up is quick enough, the gases inside the coil adhesive (similar to lacquer) releases hot gases that can create a bubble in the former. A bubbled former can be heard as a rattling sound coming from the subwoofer.

A photo of an oscilloscope screen showing clipped and normal waveforms.  

To avoid clipping, you first need to know the voltage of the signal coming from your head unit. Using source audio with consistent quality and volume level helps prevent clipping. Playing audio sources with unpredictable volume level and quality from track to track can cause the amplifier to receiving too much signal at its set gain level.

Turning down the gain on your amp reduces the power level coming from the amp to the subwoofers. Once you isolate the source of the clipping, you can set your amp levels for better performance of the subs.

OVERPOWERING YOUR SUBWOOFERS

When an amp consistently delivers more than the RMS power required for the speaker, this builds up heat in the voice coils. This extra power level builds up heat in the voice coils.

Another possibility is over-excursion from peaks in the power waveform, which can physically damage the woofer instead of causing heat buildup.

UNDERPOWERING YOUR SUBWOOFERS

If your amp isn’t powerful enough to fully drive your speakers, you’ll have to turn up the gain of the amp  for a “normal” sound level. Turning up the gain can bring in too much signal from the head unit. The amp then tries to send more power to the subs than it is designed for, clipping the signal. This under-powered situation can still cause heat buildup from the amp that will overheat the voice coil.

The best way to avoid damage is to design a system where all pieces that have compatible power handling based on your goals for the system.

Especially when partially upgrading, consider upgrades that might be necessary to your charging system to supply consistent, clean power to your audio system components.

ENCLOSURE TUNING

The tuning of your enclosure reinforces sound waves at certain frequencies. This means the subwoofer doesn’t have to work as hard to produce those frequencies. This change in the motion of the voice coils affects the impedance at certain frequencies (check out this video on box rise). This change in impedance affects the power interaction between the amp and sub. Operating well outside the tuning of your enclosure can lead to damage because of this change in the power handling dynamics.

CONCLUSION

Car audio is a highly technical subject, and there’s a lot that can go wrong. Fortunately, our customer support team are available to answer your technical questions before you damage your gear. Build your confidence by learning the fundamental concepts of electronic audio equipment. Get loud while saving time and money on replacing or repairing needless damage!