What gauge wire do I need for my subs? How exactly does the volume knob work?

Question

I have 2 subwoofers, 400W RMS, 800W max each, wired at 2 ohms each. I've looked online on http://www.powerstream.com/Wire_Size.htm, and it doesn't really say much about power, only about amperes, and I have no idea what voltage is on the amplifier output to calculate how many watts or amperes there are. So, the question is - what gauge wires do I need if I decide to wire both subwoofers to my amp in mono, and need to run at least 6 feet, preferably 15 feet long wire? I have 18 gauge wire and plan to use about 15 feet of it to connect the subwoofer - is the wire going to fry when I run 1000 watts through it? Another question - how exactly does the volume knob works? "Turn it clockwise and sound increases" is not good enough. When I turn the knob - does the voltage in the wire increase or amperage? Maybe, both?
P.S. Please stick to the topic and talk about wires and volume knobs only.
Thank you, everybody, for your effort.

Answer 1

When it comes to wire size it doesn't matter what the subs are rated at, it's what the amp can deliver and the distance. That's not to say that the wattage of the subs doesn't matter, it does relative to the amplifier. So for short runs like yours, if your amps power rating is close to your speakers power handling, then 14 would be OK, I would error to larger like 12 or 10 if you are really going to crank it. 18 is far too small for the kind of power you are talking about.

On to the volume knob. When you turn the knob the voltage and the amperage both increase. Power = Voltage x Current.

The volume control is a POT or potentiometer or basically a variable resistor, usually the resistance decreases at an increasing rate as you turn up the volume knob (an entire topic on its own). The volume knob controls the input signal to the power transistor (usually many transistors in stages). Leaving out the tech stuff a power transistor takes a small signal in and a big signal out. So putting a volume knob in the path of the input signal puts some variable resistance in the path decreasing the input signal strength. Thus a small input signal isn't amplified as much.

For example say your input signal has a rail voltage of +1v to -1v or a 2 volt range and your amp had a rail voltage of +10 to -10 or a 20 volt range. It would take a might big POT to attenuate or trim 20v, a lot of power to dissipate as heat. However 2v of the input signal is much more manageable for reasonable sized electronics.

Answer 2

Hi there.
I am an audiophile myself and have ran into the same head scratching math myself.
But, rather than make a mistake that may cost you an amp or two, here is a link that will answer just about any audio engineering question you can possibly conjure up.

http://www.polkaudio.com/education/index.php

I hope this helps. Its kinda sad that there are not as many sound engineers out there as computer geeks. I suppose it's true that the times they are a changin'.
Oh BTW, the volume knob thing. That's called an "attenuator". It allows a limited amount of current to flow through, relative to the amount of resistance adjusted for via the gain (sometimes called "Trim") pod.
See ya' :)

Answer 3

the amp should have a sub output jack on the back "one rca plug"
the best way to run the sub is LFE. try a long nicer video jack. to
plug in the left or right side of the input jack on the back of the sub .or just a long piece of cable tv wire with video jacks on the end .then you should be able to use the volume knob to adjust the power of the sub.all depending on the receiver.

Answer 4

14AWG wire will be fine. When you turn the knob, both voltage and current going to the speaker increase.