Sorry, but I have to respond to this. As an electronics engineer and fanatic, I can't help it, I just have to.
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Originally Posted by coolice
I wouldn't be entierly convinced your idea of using an 8ohm subb woofer will necassarily help in reducing the current draw down the power line. While good in theory the amp is still going to pull it's required amps regardless of what is connected at the end of it, only then when power is at the amp will the amp itself then run cooler through the 8ohm subb loading it up a bit more and not allwoing the power to flow so freely.
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You have a bit of a strange idea about power, current, and so on.
An 8 ohm load draws only half the current of a 4 ohm load. You say that the input current is about just as high. Well then, where does the rest of the current go then? And more, since
U = R x I (voltage = resistance x current)
and
P = U x I (power : current x voltage)
we can derive
P = R x IČ
That would mean that, if indeed the current would be constant, the 8 ohm speaker delivers twice the power of the 4 ohm...
Sorry man, wrong there...
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Just thinking about this somemore (it's been a while since I've had to think of this) an 8ohm load is going to add more resistance to the amp, hence power will backup. A 4ohm load allows the power ffrom the amp to flow more freely.
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What does "power run freely" mean? An output stage of an amp delivers some current to the load, and depending on the output impedance (which should be as low as possible) that results in a voltage across the load, and some voltage across the output impedance, called "loss". That's why them things get hot!
Keeping that in mind, you will understand that the loss is lower when the amp is loaded with 8 ohms instead of 4 ohms.
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Lets not forget an 8ohm subb connected to the bridged output of an amp will be seen as a 4ohm load at the amp anyway, load ~ divided by 2 (as it's on the bridged output) = 4 ohms at the amp.
A 4ohm subb will present a 2ohm load at the amp, current will flow more freely and the RMS power goes up.
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That's not how it works, however going deeper into this would take me far into schematics and theory.
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We need to bear in mind that electricity does not flow in the wires but along the out side of it, hence good quality audio power cable has multiple thin strands of wire which increases the surface area of the wire compared to it's size.
Even though the car cabling will be of good quailty it wont have a high strand count and as amps are pulled it will not be as capable of delivering them as well as a multi strand cable.
For safety I'd say fit an 8 gauge power cable minimum from a fused connection under the bonnet to the boot. It's a pain but will be safest and should you have a fire your insurance company cannot say it was the faulty ICE install.
Pulling major amps down a thin wire will make it heat up and it's near plastics & carpet.
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It is indeed ALWAYS better to install power supply cables as thick as possible, with as low resistance as possible. Even a very low resistive loss costs power at the end. Suppose that the cable from battery to amp has only 0,1 ohm resistance, which is not bad at all! For a 240 watt RMS amp it would carry 20 amps, meaning a loss of 2 volts! So your amp wouldn't be getting 12 volts, but only 10... (Simplified calculations). That's also where these big electrolytic capacitors come into play: they flatten out the load peaks, so the current in the supply cables is less peaky, and you'll have a more steady supply, and less loss.
K.
K.