Few weeks ago, a member of CHIP’s forum asked me why do we need a powerful subwoofer (with big magnet, stiff/hard cone, and lots of power) in car audio application?

The question was actually simple, but it took time for me to answer it (since I had forgotten my physic class, anyway I was in social class, not science).

Before answering this, I want to turn back few years ago at my senior high age. At physic class, we all know the equation below:

Speed of sound = Wave Length x Frequency
c = λ * f
The standard for c (speed of sound) is 343 metre/second.
Let’s say we want to hear the low frequency at 30 Hz.
So, the wavelength is about 11.43 metre (343 divided by 30).The minimum range to hear this 30 Hz is about 1/4 of the wavelength or about 2.8575 metre.Do you have this distance from you subwoofer (at back seat or trunk) to your ears (driver’s ears)? I don’t think so. So, how can you enjoy this low frequency? That’s why most of the car subwoofer is designed with big magnet, stiff cone, weight materials, and big power handling. By doing this way, we all hope that the subwoofer can push the low to the highest limit and make sure that you can enjoy the low frequency (and eliminate shortest distance problem).

Earthquake Subwoofer

Picture above is Earthquake HoLeeS15 15″ Elite Competition Subwoofer.
Over 45 Kgs or 100 lbs, has dual 1 Ohm 4″x8″ voice coils (over 7000 RMS each) and over 4″ long throw excursion! Ready to rumble, eh?
So, what makes the car subwoofer different from home subwoofer?
Nothing special (I guess). Some car subwoofer are designed with low impedance (could be as low as 1 Ohm), so you will need a high current amplifier or put them in pararel configuration to achive lower impedance. The rest parameters shouldn’t be special. They all use the same T/S standard. You can input these parameters to your loudspeaker box designer (like WinISD) and design a correct box, even for your home use.I’m not saying that all car subwoofer can be used at home. It’s possible, but it depends on the designer of the subwoofer itself (whether he/she is able to design a correct box with these car drivers). It’s not about the gun, but the man (or woman) behind it.