QuestionHi I just bought an Infinity Reference 12" Subwoofer for my car. It is 1245Watts Peak and 300 RMS. The amp I'm trying to Use is a Rockford Fosgate 360Watt Punch 2 channel amp. And the sub is DVC 4 ohm.
The sounds really great when the volume is very low....very low. As soon as you get past about 10 on the head unit you cant hear the sub anymore and all the lights in the car dim a lot. including the instrument cluster and everything. My question is, is the amp insufficient or is this perhaps a problem with my charging system???
I followed a wiring diagram on rockford fosgate for a 2 ohm load. The amp is bridged. Maybe the sub cant take 2 ohm???
AnswerHello Tony,
You have discovered the dirty secret of car audio. The vast majority of high power installed systems cannot provide their rated power because the car electrical systems are almost never designed to support that kind of extraneous power consumption. First off, some basics. Your battery is NOT the power supply. Your battery is there to provide a high impulsive current to make the starter motor (which runs on DC) spin so the engine will follow. When the engine starts, it turns the generator (ALTERNATOR) which charges your 12 volt battery, by putting about 14.4 volts across it. When you suck SO MUCH power from your alternator that it runs out of available current, the voltage drops, and you have to run off the battery. If you pull out your car amplifier data sheets, and look closely, you will note the power they supply is only rated at 14.4 volts (off your alternator) not 12 volts (your battery). At 12 volts it might work, but with considerably less power. When you turn up your system, it seems either the overcurrent protection, or under-voltage protection on the amp activates, turning off your sub and killing your bass. Go online or call your auto dealer and ask them what is the continuous current available from the alternator. Let's assume you have a big alternator and it can supply around 100 amps. (Typical would be 65 amps) At 14.4volts, that equates to 1440 watts total. (Power = Volts * Amps) If it takes 300 watts to run the automobile, then you have 1140 to spare before you start to overload the alternator. (As you call it the charging system). If your amp is 65% efficient (typical) then out of the 1140 watts available, you can get (1140 * 0.65 = 741 watts). If your amps need to deliver more continuous power than this, you will have the voltage drop (which makes the amps pull even MORE current) the lights dim, and the whole system is at risk of failing. Your car stereo dealer won't tell you this. First off, they don't know, secondly if they did and told you you would not spend your money there, you'd be spending it first buying a bigger alternator. As far as the sub "taking" two ohms, the comment does not make sense. The sub-amplifier is either "2 ohm stable" or not. The speaker is what it is, and it is up to the amplifier to supply the power. The speakers job is to absorb and convert as much as it can. By the way, the average car audio sub converts about 0.5% into sound (that is half of one percent, not 50%). Talk about Global warming!
