wiring gauge to amplifier

It appears you are talking about POWER and GROUND, not speaker wire.  You need to use the proper gauge wire for the current draw of your amp.  I recommend 4-AWG for both power and ground for your 400 watt amplifier if the total length from your battery to the amp is 10 feet or more.  If it's less than 10 feet, you can get away using 8 AWG.  Remove the 10 AWG wire from your car.  Be sure to fuse your power wire at the battery - if your use 4 AWG you can use up to a 150-amp fuse.  If 8 AWG, up to 100 amps.

Using the correct size power wire will not make the sub hit harder or play lower, but it will keep your vehicle from burning to the ground due to the amplifier power draw through the wire.

Custom Audio NY-

I will give you an example from Introduction to Electroacoustics and Audio Amplifier Design by W. Marshall Leach, Jr. Chapter 12, pg 261, example 28.

It is desired to design a stereo amplifier that will put out 100W of average power per channel into two 8 ohm loads.  It is estimated that the power supply voltage drops 10% at maximumpower output and that the amplifier clipping voltage is 7V lower than the power supply voltage. Calculate the required no-load power supply voltages.

Vclip = sqrt(2*Rload*Paverage) = sqrt(2*8*100) = 40V

The power supply voltages are thus given by plus and minus (40+ Vdrop)/0.9; Vdrop is the drop across the output transistors, which we will assume is 5V. So supply rails = +\- (40+5)/0.9 = +\-50V

The amplifier input will desire enough current  at the input so that the rails wil reach +\- 50V, the voltage at the input will drop but the amplifier can't easily demande more voltage like it can current.  The larger gauge input wire is used so there is less resistance in the wire when the amplifier has an increaed current demand for a large power output, which you already know.  I hope this helped you out.

DYohn answered the power wire precisely for the original question.

OK...so what we learned here is that using a wire that is a gauge or so too small..will burn up the amp..and/or burn the car down????? Did someone put a 150a fuse on a 10ga wire or did I miss something here??

Maybe if the speaker wire is too small it will slip out from under the carpet and a pet will choke on it..or..catch someones foot and they could trip and fall......hey..it's a possibility right?

Well anything is a possability......but statstics says the pet thing is unlikely. If you used a wire gauge that is too small but fused properly then you will likely keep blowing the fuse on the power wire and be replacing it constantly which really has no point.  If it is fused to high or you run it to the extreme continuously without blowing the fuse then you wil be shortening the lifespan of your amp over time, you probably won't burn it up instantly.

Personally, I don't like replacing fuse constantly, and I don't like to replace my equipment all the time.  Let me rephrase that...I can't afford to replace my equipment all the time, I would always like to come January, but the wife would not approve.

Ok... thanks again everyone for helping explain.For a while there it seemed to be bordering on the absurd..which Is why I mentioned the pet choking thing..a little sarcarsm to lighten things up.

Anyhow...some things I may also need help with on the subject.  Were discussing situations in which voltage fluctuates constantly..such as in a vehicle. I would assume some kind of voltage regulation is used in any 12v automotive amplifer to help compensate..for normal as well has more extreme fluctuations.

But regardless......dealing with this specific post..and my original reply...lets take this example.

Ok..a 400w amp....and a 15ft run of power wire. For the sake of this dicussion I will leave out fusing and other obvious issues..I just want to deal with wire gauge and what I belive the effects should be.

I used math..ohms law and a current draw calulator.I came to these conclusions...

using ohms law@ 12v the maximum current draw should beroughly 33.3a. At 14.4....roughly  27.7. So I averaged the current draw to be 30a @ 400w.

using a 4ga wire..(resistance of .25m ohm per foot) a run of 15 feet will have a Vdrop of  approx. .11v.

An 8ga. (.63m ohm per foot) @ 15 feet = Vdrop of  approx .28v.

A 10ga. (a little under 1ohm for a 15 ft run) should have a Vdrop of approx .44v..less then 1/2 a volt.

And these calculations are maximum assuming max draw at all times.

So I guess where I am going with this is does anyone really belive the difference in voltage drop using the 10ga is really enough to burn stuff up??  The normal voltage fluctuations in a vehicle far exceed the difference in Vdrop caused by the wire gauge...and remember..I am talking about the question from the OP..not hypotheticals or sytems running at 1ohm..or massive current draw that exceeds the limits of conventional charging systems etc.

Now before anyone jumps on me..lol...PLEASE realize I am not trying to arugue that it is ok to use a smaller wire ga. then required..I never do that..as a matter of fact I am notorious for overkill when it comes to audio system wire size...but it is the reason why I use the larger wire we seem to have some differnet opinion about..well at least in the case with this 400w amp.

Where I do have some issue...is believing that in this particular post ..that the extra heat caused by using a 10 ga wire would be substantial enough to cause concern...or should there be concern..but perhaps about as much as a pet choking on a speaker wire..lol sorry had to add that. I do plan on doing some experiments with wire gauge and amp temp in the future..I want to find out how much difference it make as far as heat being a major concern. I won't bother with anything ridiclous like running a 1000w amp off an 18ga..although it would be fun watching the wire insulation burn off..but something similar to this situation where using "border line" wire ga. vs. whats called for  vs. overkill.

Thanks again guys..great stuff.

Please keep in mind that this is a widely read forum whose history has been to provide basic fundamental truths about the workings of car audio.  New members often find answers to their own questions without ever posting, as can be seen by looking through the general membership list at the number of members who never posted a single question.  Answers, generally, are purposefully blunt and to the point.

The gist of this OP's concern is about power wire gauge.  Specifically, he doesn't understand the importance of using the appropriate or recommended gauge, so he asked if it was an issue to be concerned with.  There are other readers who want to know this, too; most with different specifics than those related here.  The answer that you are taking issue with is about basics and encourages all readers to realize the importance of wire gauge.

stevdart, I think you may have taken that statement out of context......(that happen here???lol) I didn't mean to imply that anything discussed on this post was not extremely useful information..or that I had "issue" with any replies per say.

The OP simply asked "Will I get better deeper bass by switching to the 4 gauge." I replied in a way that reflects what I have experienced.....more voltage will in most cases..produce more output. And more voltage will definatly be a side effect of using the proper gauge. 

Now others mentioning that he will not notice a difference in bass output.....right there we have debate???  right??

Now there is nothing wrong with debate..and there is nothing wrong with mentioning other factors that come into play when dealing with wire gauge. But when I started reading replies about amplifiers burning up...and wires melting down..well at that point I needed to attempt to put things into perspective.

I would rather people use the proper gauge in any situation....but I will debate anything I either don't understand...don't believe to be true...absurd.. an exaggeration or taken out of context.

Is there anything wrong with that.?..People should learn all sides..not just be frightened into thinking stuff will burn up when it's not going to happen. Or if it is going to happen..I would like some convincing, conclusive evidence.

In closing..I had a disagreement with a reply...should I be shunned from debating? Perhaps this place isn't for me.