theratdude64

amps * volts = watts /2

How and where can I find those numbers for my amp? And whats the resulting number mean? Im working with a 4ch 2000w amp and we have the front and rear RCAs from the headunit plugged into it so that each sub has a full input not a shared one... A day or two after hooking it up like that, the subs now just make a pulsing sound. A car audio place said its 12 guage wire, im damn sure its 8, does he need like 4 or 2? Any idea what the pulsing means? It worked fine for like 2 days that way ,and for a while with just one set of RCAs into it

Thanks

blyth18md

I think your formula is a little off. I was taught that...

amps * volts = watts

yes thats the first step

you get the "amps" figure buy plugging in the total rating of the fuses on the amp. (so if you have (2) 15 amp fuses, you'd substitute 30 in the equation)

so it would look like...

30*volts= watts

to get the volts rating you simply figure in fact that cars are set up for 12 volt systems, the output is usually between 11-14...a 12.8 or 13.8 is a typical reading.

so it now looks like

30*13.8 = watts

which equals

30*13.8= 414 watts

Now heres where you need to remember a lot of little factors.
First off the equation above is setup to figure out the max power that amp could put out. since if it was drawing 30 amps ..it would be popping fuses..

to figure out the RMS rating of the amp you multiply that answer times .707(the numeric value of Root Mean Square). So...

30*13.8=414 watts MAX

414 * .707= 292.70 RMS

Ok so now your thinkin ok 300 watts steady aint bad for that fuse rating....well So far these numbers have been calculated without factoring in effeciency ratings. As we all no no amp is 100% effecient, very few amps you can find are even close to 80% effecient. And different class amps have different characteristics when it comes down to effeciency. Amps range from very low to pretty high effeciency. decent amps range from 50-70% effeciency...so now to factor in the effeciency rating...

292.70 * .60 = 175.62 REAL RMS


Once again my methods may be flawed slightly but this is just a general way of giving you a ball park figure. So when your pyramid amp says 2000 watts and it has a 30 amp fuse you know its rating is bogus.
Not to say some high end amps wont have lower fuse rating than some lower end amps, but still put out more power, you have to remember higher end companies can afford to use better qaulity components resulting in a more effecient product.

I hope this helps out

blyth18md

Oh yeah i forgot to mention that is only for its total outputif it was a four channel amp you would take the "REAL RMS" rating and divide it by the number of channels....

Example

175.62 / 4 = 43.905 REAL WATTS RMS PER CHANNEL

theratdude64

whoa, thats the best way ive heard it said, thanks man

Ok, im running my numbers through, I have 2 20A Fuses so 40

40*12.8 or so is 512

Is that per channel? so the whole amp is 1024? And RMS is 362?
What numbers do I use for this? http://www.crutchfield.com/installgu...ble_gauge.html

Thanks! :lala:

blyth18md

40 amps * 12.8 volts = 512 PEAK Total power
512 PEAK * .707(RMS) = 362 RMS Total power

then if its a 4 channel amp you divide that by 4

362/4= 90.5 RMS per channel

But EFFECIENCY IS A MAJOR FACTOR

90.5 * .65% effeciency = 59 RMS per Channel.

Got it yet?

theratdude64

How is this right? 40*12.8 = 512peak power 361.984rms , 235.2896 Effency RMS, why is 512 the peak if the amp advertizes 1k?

Also, we just rewired the 8 guage in my friends car to some nice 4 guage. He put the bandpass box pointing against the backseat, shouldt it face towards the rear of the car to sound better? For a 2000W 4 channel amp with 4 Guage Wire and 750w Kenwood 12s, its pretty weak, any ideas how to "beef" it up?

Thanks for helpin!

blyth18md

Because in car audio you get what you pay for bottom line.
they have to advertise 1000 watts to sell there amps because people new to the audio game will only look at how many watts its rated at.
Now you now there are more factors than what the amp says in big print on it, as a matter of fact i think every amp that has two inch letters saying "2000 watts" is really extremly overrated
I dont know why, maybe they test rate there amps in prestine conditions with 20 volts of power or something cleaver to get around false advertising

junkyarddog

blyth18md is right, the 2000 watt amp would not work with those fuses and 12 gauge wire.

anything used for audio would be between 50% and 78.5% efficient. Unless you are using a class D amp.

the formula is: power in (watts) = power out over efficiency (i.e. 50%)

junkyarddog

in order to beef it up, I would need to know some more details about you setup.

1. did you use 4 awg for the ground connection, did you ground it to bare metal on a 'primary' part of the unibody?
2. did you terminate the wires properly?

(I've seen guys trim some strands from a heavy gauge wire to fit it into a smaller terminal........this would make it a lighter gauge wire. don't laugh, I've seen professionals do this!)

3. How are your subs connected?
4. What kind of amp do you have?
5. Describe the box, is it homemade, ported, diminsions?

theratdude64

Its not 12 guage, the idiot shop at best buy said it was because they thought he was an idiot and to buy something from them. It was 8 because it origionally had a weaker system, but today we just wired in a 4 guage. So its plenty stocked.


the subs were wired normal ch1&2 to one sub, and ch3&4 to the other. That was really weak and so we brided 1&2 to one sub and 3&4 to the other. The HU has RCAs coming off the front and rear, so its got 2 sets of inputs. THe ground is no longer than 18inches 4 guage wire. Everything is connected so securely that they dont even wiggle. We have a huge fuse under the hood by the battery. The box is a Homemade bandpass, and i suspect that it leaks out the glass.... I found the amp here: http://www.dragondistributing.com/bossripper.htm *its the RIP995) and heres pics of things (btw the subs arent in that car, thats my dads and we just set it there while we were workin on it )

theratdude64

oops, heres the pic

Makaveli

i have a rockford fosgate power 451s amp. rated at 450 watts RMS bridged at 4 ohms, on the sheet with the amp it reads 464 watts rms.

40 amp fuse x 14 volts = 564
564 x .707 = 398.748
398.748 x .64 = 255

so does this mean its not 450ish bridged, its closer to 300?

http://www.crutchfield.com/cgi-bin/S...=0&cc=01&avf=N

blyth18md

like i said there many factors that determine what the amp puts out, you figure rockford is a big company with good solid equipment, which translates into them being able to afford better, more effecient parts. Also you can bet that that amp was tested at 14 volts constant..in the car enviroment 14 volts is hard to mantain...unless you set out from the beginning with those plans in mind...usually in car you'll be running around 12.8

theres so many factors, this formula cant give you an exact number it just a good thing to know when youre shopping for amps, it'll give you a good ballpark figure..
the only way to be sure is to have you amp bench tested at the same voltage rate that your car puts out.
If its loud enough fro you, what are you worrying about? you know what i mean?

Makaveli

that makes sense now, hahaha, never thought of all the things that come into play. just wondering, since the formula seemed a little odd at first, to someone whos not that big into audio equipment anymore