Myths of Car Audio #1

I have to disagree

Under powering a subwoofer, especially a high-end designed for large wattage, can definately harm if not blow a speaker.

"Having too little power blows woofers"

Lets say you have a subwoofer with a 500w peak / 250w rms handling, and have an amp that is 150w X 2 peak / 70w X 2 rms. The key is RMS! This amp can blow the sub given that the amp does not have sufficient power to push the woofer at nominal levels. Even if you increase the volume to its max, you are also increasing disstortion, which is the most common killer for woofers.

You need to find an amp whose RMS is almost the same if not more than the subwoofer. Never go by peak power.

My example is very general. Any audio junkie knows that variables such as voltage output, disstiortion, and enclosure can change the outcome. I have seen a customer with a brand new JENSEN amp rated at 1,000w; the disstortion and heat rating were soo poor that amp barely made 150w RMS per channel.

underpowered speakers go bad because they overheat.

the speaker's diaphragm is attached to a metal coil "voice coil" that is suspended inside of a magnet. alternating current pushes the coil in and out, transducing the electrical signal into sound waves.

since we're talking about an electrically charged magnet, we're talking about heat. the heat is dissipated by actually powering the woofer. keeping it in motion disperses the heat rather well. underpower the woofer, and your voice coil isn't moving as much. over time, the coil can get hot enough to snap.

it's perfectly healthy to overpower a subwoofer, if done right. it's actually quite safer than underpowering it. i'm sure we all know peak wattage ratings are nothing but marketing, so anywhere between 5 to 10 percent over the RMS rating should be fine.

people who blow their speakers and blame it on overpowering either gave them too much power, or just turned them up too damned loud.

always be good to your ears. you'll be glad you preserved your hearing when you get old

Actually the problem is the low power amp gets turned up to the point it is constantly clipping. Yes, heat is the enemy, but it's not because the voice coil isn't moving enough, it's because the amp is clipping hard and applying what amounts to DC (sound waves are AC) to the voice coil. They won't tolerate that for long without frying unless you put a DC blocking capacitor inline with the speaker. With modern amps, it's very possible to have a straight DC output with a sufficiently large input. Most high-end home audio has very low frequency blocking built-in to prevent this.

The other contributing factor is 12v automotive electrics. If you only have 12 v to work with, you've got to run a LOT of current to make even 120 watts. 10 amps at 12 v (120W) is a LOT of current to run through a voice coil. Car audio will be a lot better when the new 48v automotive standards take effect (should be 2007?). You won't need nearly as much current for high power, and the wiring harnesses in cars will get a lot smaller and lighter with the generally reduced current requirements that come with a higher system voltage.

Saying it's perfectly healthy to overpower any speaker isn't quite accurate. It's common to use a bigger amp than the speaker's rating, but if you drive it too hard, you'll damage the cone suspension (or if you're smart, blow a fuse). These days with woofers as large as some people are putting in mobile systems, you'd be hard pressed to over-power the speakers, but it can be done.