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Discussion Starter · #1 ·
I'm looking for opinions on whether or not the following changes to the primary current carrying cable from the battery to my amp(s) will be realisticly noticeable from a hearing standpoint. For simplification, ignore the speaker wire sizes and efficiency of the amps.

Current setup: 600 watts rms @ 14.2 volts = 42 amps (perfect world, no line loss).
6 gauge wire, 12 feet total length (10 ft for the positive, 2 ft for the negative)

According to the Rockford Fosgate website, with 6 gauge wire I'm loosing 20 watts (or 3.5%) to line losses.

If I replace the 6 gauge with a 4 gauge, the line loss will be 13 watts (2%). If I replace the 6 gauge with a 2 gauge, the line loss will be 8 watts (1.5%).

Realistically speaking, will the volume (or subwoofer punch) change be noticeable going from 20 watts lost out of 600 to 13 or 8 watts lost out of 600?

If you have a reply based on experience I'd love to hear from you. However, anybody who really believes that a capacitor is beneficial will help out, or anything else other than worthless need not respond.

Thanks!
 

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that would be the least of my worries.... your really stopping fires when you go with a larger gauge.... try knukonceptz.com for wires
 

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line loss of wire??? your amp is pulling 42 amps of current....period...where are you "losing" power????? the wire is not draining wattage from your amp...ohms law...the wire makes it pull 3.5% power...meaning your 600 watt is acting as 620 watts.......

this would make no benefit to sound quality.....unless your amp cuts out due to insufficent power....

everytime i put a system in i used 4awg minimum because you never know when you would add another amp....only time i didnt is with my 3, because i only put in a 150rms amp fomr my 8" sub....which obviously doesnt need 4awg
 

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Discussion Starter · #4 ·
I guess where I'm going with this is that any line loss will have a corresponding voltage drop (ask any electrician). A voltage drop may or may not have an effect in this situation.

Watts = Voltage X Amps. So if the voltage seen by the amp decreases from say 14 volts to 12 volts, and the amperage being drawn from the amp stays more or less the same or decreases with the lower voltage, then watts has to decrease, resulting in a volume loss.

The heart of the original question, regardless if you agree with my interpretation of the effect of ohm's law or not as it pertains to the audio amplifiers, is that would you honestly hear a difference in an amp producing 580 watts of sound vs. 587 or 592 watts?

Likewise, if I mod my engine to increase my horsepower by 2%, would you, the driver, even going to notice it for all practical purposes? I could be wrong but I don't think I would.


I do appreciate the feedback and I hope this clarifies a little what I'm trying to ask. Thanks!!
 

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You're not going to notice any difference. You will see around .05-.1 gain in Db by changing the wire. 1Db is what is considered to be audible to the human ear. In theory doubling the power of your amp from 600 to 1200 would net you a 3Db gain.
 

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This may not directly address your question, but just a comment.

I think you overlooked something in your calculations. An amp that has an output of 600 watts will draw more than 42 amps. Your formula assumes the amp to be 100% efficient. Class AB amps are probably closer to 50%, while a class D is higher. You can't just divide 600/14.2. A class AB amp will consume closer to 1200w in order to output 600. If you want to get the math precisely right, you'll have to take this into account.

That being said, I am positive you would not notice an audible difference going from 4 to 6 ga.
 

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[quote author=squidchief link=topic=139626.msg3010016#msg3010016 date=1237751679]
I guess where I'm going with this is that any line loss will have a corresponding voltage drop (ask any electrician). A voltage drop may or may not have an effect in this situation.
[/quote]

It is true that there will be a slight voltage drop. If you draw out the schematic, you could represent the power wire with a resistor (albeit with a minuscule value). There is always a voltage drop across a resistor. By going from 4 to 6 gauge you might go from .001 ohms to .0015 ohms (just pulling numbers out of my @ss for an example). If you've got 14.2v at the battery terminal, this may take it from 14.19v at the amp for a 4ga wire to 14.18v with 6 ga. (again not actual numbers, just a fictional example to illustrate the concept).

There will be a difference, but it may be so small that you can't even measure it with your DMM.
 

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[quote author=gar187er link=topic=139626.msg3009757#msg3009757 date=1237738578]
line loss of wire??? your amp is pulling 42 amps of current....period...where are you "losing" power????? the wire is not draining wattage from your amp...ohms law...the wire makes it pull 3.5% power...meaning your 600 watt is acting as 620 watts.......
[/quote]

Wire is a resistor. The resistance of any given wire is related to the material it is made of, the length of the run, and the cross-sectional area of the wire (the gauge). The longer the run, or the smaller the gauge, then the higher the resistance. What is happening is that at higher power levels the wire is actually converting the electricity flowing through it into heat - and that extra energy is never making it to the amp.

To the OP:

Here is a great site for issues like this:
http://bcae1.com/wire.htm

Generally as a very rough rule of thumb, when I want to get an idea of how many amp the manufacturers think an amp will pull I look at the fuses they built into it. The total of the fuses is going to be slightly more than the amp is designed to draw (try this on a cheap swap meet amp - it's kind of a give-away when it says it puts out 2kw and it's got only a 20a fuse).

i like to do the math as well, but as speedbump pointed out amps are not very efficient and you need to take that into account (also, as far as class D amps go, yes they can be as high as 80% efficient, but that is usually at about 2/3 their max power output. when they get up to full output they usually drop back to similar efficiency as class a/b amps)

Given all that, I think you're probably ok with the 6ga wire for now, but if you get any bigger of an amp or add on a 4channel amp ( I assume you are driving a sub with this amp), then upgraded would definitely be necessary. I have personally noticed a difference going from 8ga power runs to 4ga, but 6ga is kind of an odd size that we never used or saw at my shop.

As for voltage drop, a half volt is usually the maximum that is considered acceptable. Keep in mind you won't be able to measure the resistance of the wire with an ohm meter becasue the meter does not present a load to the wire. Voltage drop is really the only way to check without a specialized meter.
 

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Discussion Starter · #9 ·
Thanks for all the input! I fully understand about the efficiencies of the amps and how it factors into how much current you actually draw for "X" amount of output. Let me explain what I had and what I have now.

The 600 watts is actually from 2 amps: An Alpine 4 channel 200 watt RMS, and an Alpine mono 400 watt RMS. I had both amps off of a single 10 gauge wire that was about 12 feet long. The lights would dim and pulse with the music, my digital voltmeter would show the voltage frequently dip down to 12 to 12.5.

I did 2 things at the same time: I did the "big 3" whereas I added 4 gauge cable to the existing alternator, engine ground, and chassis ground. This gave me an effective 2 gauge wire for each of the 3 lines (assuming the original cables were 6 gauge - they looked smaller than the 4 gauge). The now four ground wires are junctioned to two 2 gauge wires to the negative post. Then I ran an 8 foot 6 gauge positive cable from the battery (fused at 80 amps) to a junction box where it then split to two 6 gauge lines about a foot or so long to each amp.

What did I see and hear differently? The lights no longer dim and pulse. The volts almost never go below 13.5 under a heavy amp load (almost a volt increase from before). This I attribute to the "big 3". On the sound side, the volume is definitely louder at the same volume setting I had before. Also, the sub definitely has a more distinctive punch to it than before. This I attribute to the new power line being 6 gauge at 8-9 feet long vs. the 10 gauge at about 12 feet long.

I don't know if I would hear an even better result if I changed the 6 gauge going to the amps to a 4, but I am very pleased with what I have now. If I max out on my personal volume comfort level with plenty of volume control still available to push "clean sound", then it's good enough for me.

If it was any louder, blood would be coming out of my ears. (ok, maybe a slight exaggeration but you get the point).
 

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the volt difference that is the key is the difference between at the battery and at the amp. If you're seeing more than .5v difference under load, then larger wire would help.
 

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When I chose my wiring kit I bought the one that had fuses that were the same or somewhat larger than my amp. I thought this was a good guide on how much power the wire kit manufacturer was expecting the wire to carry.

There is little sonic advantage to oversized wires. It is just wasted money, extra enviromental degradation, and weight.
 

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Discussion Starter · #12 ·
I guess one of the ways I can "see" the line loss is to put a steady tone through the amps and take a voltage measurement at the battery and another at the terminals of the amps.

Is the general consensus out there that if I have more than a .5 volt drop at the amps that I should increase my wire size?
 

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Yes that would be the way to test it. Keep in mind though that you are also putting your ground connections and return path into the equation. Since you've done the big three already (and I'm assuming you've got the cleanest ground point possible), there's not much you can do to help that.

Honestly, I think that with the amps you are currently running you are probably fine with 6 ga for now. Esp given that your happy with the way it all sounds now.

Also keep in mind that test tones carry a lot more power than music and will both draw a higher load than music (not a bad thing for the test) but you will also be running a lot more power through your subs than normal so watch that you don't burn them out.
 

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Discussion Starter · #14 ·
Automaticman,

Thanks for the feedback. I'll post the results of my test.

I'll probably put my other meter - an inductive amp meter, on the line to keep below the amp's fuse blowing point. The one amp is a mono amp with two 20 amp fuses - I'll assume that they are wired internally in parallel to give me an effective fuse of about 40 amps. The other amp is a 4 channel with a 30 amp fuse (two 15's).

That gives me a theoretical maximum of about 70 amps I can draw between the 2 amps. Realistically though, if playing music will draw approx 1/3 the amperage of a pure sine wave ( as per some technical documents I've read), then real world average amperage draw should max out at around 23 amps. And that is of course if I am listening to the music loud enough to make my ears bleed.

I should have no current carrying issues with the 6 gauge at that amount of amps.
 

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those are all pretty safe bets. But transients can drive the amperage up pretty high in spikes, especially on the sub amp. Either way, with those amps, I think you're probably ok. It also depends on what you listen to. Either way it will be very interesting to see how the test goes. Be sure to test with a variety of music at different listening levels just to see what the current draw differences are.

I saw my system hit as high as 200 amps when I accidentally wired my sub in parallel and bridged a 1ohm load to my 2ch amp (designed to output 1000w into a 2 or 4 ohm load, it took the half ohm load like a champ - until a realized my mistake after about a minute), wired correctly I see it usually draws around 60amps and moderate high volumes.
 

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Discussion Starter · #16 ·
Ok, here are the results of my test.

Setup:

- 12 feet of 6 gauge wire. Negative side not counted as it is about 6 inches long. (I misspoke on my original post).

- one 400 watt rms class D mono amplifier, one 200 watt rms class AB four channel amplifier.

- 50 hz steady test tone. I figured that since the mono sub amplifier can pull almost 2X the amps as the four channel, I would maximize the current drawn with the 50hz.

- Engine running. 99% of the time I'll be driving when rocking out.

- Set the current drawn as measured just before the main 6 gauge line splits to the two 6 gauge lines to the 2 amplifiers at 28 amps. At approx 14 volts this gave me about 400 watts split between the two amplifiers, figuring the sub amp would be drawing more out of the two due to it's gain set higher.

Again, remember we are dealing with a pure sine wave, not music. I didn't feel it was necessary to max the amplifiers out 100% for this test and risk damaging the equipment. 50 hz is pretty demanding on smaller speakers, I didn't want to stress out the door speakers any more than I had to (Pioneer TS-A6872R).

- 3 meters. One a clamp dc ammeter and two multimeters - one on the battery, one on the amplifier. The two multimeters had a .17 volt difference before the test. This difference has been factored into the under load readings for an "apples to apples" voltage reading at both locations.


Results:

- at 28 total amps being drawn by the two amplifiers, the voltage at the battery was 14.29.
- the voltage at the mono amplifier was 14.07.
- this makes for a voltage loss of .22 volts ( 1.5%).
- with amplifier efficiency factored in, the test generated approx 268 watts out to the speakers.


Real World with Efficiency Calculated:

If you factor in the efficiencies of the amplifiers, the amplifiers are going to draw more amps to get the same watts out. If we assume that the class D amplifier is 85% efficient and the AB class amp is 50% efficient, that will give me a combined efficiency of about 68%. I will need about 63 amps at 14 volts (882 watts) to get the full combined 600 watt rms output of the amplifiers.
That will put me over the .5 volt drop self-imposed limit (actually a .74 volt drop). Over 42 amps I'll need a 4 gauge wire. At 63 amps with a 4 gauge wire would give me an approx .48 volt drop.


Summary / Opinion:

For the volume I'm normally going to be listening at, I'd say that's not too bad. Granted the voltage loss will increase as the amperage drawn increases. As per a couple of voltage drop calculators I found on line, my actual voltage drop at 28 amps was very very close to what the calculators said it would be. As it stands now, with the amplifier(s) efficiency calculated, I'll get about 400 watts rms out with 42 amps being drawn with a .5 volt drop. However, an additional .24 volts dropped to get my full rms output really isn't that bad.

I may replace the 6 gauge with a 4 one day, but I doubt I'd hear a difference. After seeing that I only generated 268 watts on the test made me wish I pushed the system harder to get a better feel for the voltage losses but I didn't know how stressful a 50 hz pure sinewave tone would be to my door speakers. I really don't need blown speakers right now.

Sorry for the long post but once I got going, I wanted to explain it all. If someone sees any errors in my calculations or assumptions, please let me know.
 

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Great job!

The one thing to watch out for is the efficiency of the class d amp, that number will drop considerable after it get above about 2/3 its power rating. Other then that I'd say all your reason is pretty fair. i hear you about not wanting to blow a speaker, but I do hope you have crossovers on the front speakers anyway.

In the end, I think that if you ever decide to change or upgrade an amp, that would be the time to change the wire. I think you're fine until then though.

So at that amperage draw, how loud was the sound in comparison to what you listen to music at?
 

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Discussion Starter · #18 ·
I agree. I probably won't mess with it until I do another mod or upgrade.

As far as the volume goes, I can't say. The test was just on a 50 hz tone. I don't think my clamp on ammeter has a fast enough response time to accurately track music. Probably would need one that has something like an average over "x" time mode. I might try it though next time I have to play around with the system.

I can say that I can raise the volume to the point where the sound level becomes very uncomfortable (which btw by most people's standards is VERY loud), and the music is still crystal clear with no distortion.
 

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[quote author=squidchief link=topic=139626.msg3026234#msg3026234 date=1238414183]

I can say that I can raise the volume to the point where the sound level becomes very uncomfortable (which btw by most people's standards is VERY loud), and the music is still crystal clear with no distortion.
[/quote]

Really I think this says it all
 
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