2-Channel Amp---4 Speakers

korek28 · 10-25-2006, 04:45 PM

Ok here is my situation:
I was thinking of getting a set each of Polk db650 and Polk db675 speakers ( both 6-60 W RMS ) for my car once I finish up my Car PC project soon.
Now since I want to completely remove the head-unit from the car and run the sound directly from my PC to the speakers, I will be getting a Rockford Fosgate P3002 ( 2-channel amp, 75 W RMS x 2 ) to power the speakers.

My question is:
Since the amp is 2-channels and I will be running 4 speakers from it, does that mean once I split each channel to power 2 speakers each ( 2 channels x 2 speakers per channel = 4 speakers ), that each speakers will only get half the power ? Will each speaker get only half of the 75 W RMS ?

Thanks for any help on this.

XC-C30 · 10-25-2006, 05:19 PM

you'll have to wire up front and rear of each side, that way you'll play at 2 ohm. BUT, in that case the dampingfactor of your amp will draw back, and soundquality will be drawn back also. so what's the power output of your amp at 2 Ohm? it should be around 120watts RMS per channel, for you to get full advantage of the speakers.

korek28 · 10-25-2006, 05:37 PM

Quote: Originally Posted by IC-C30

so what's the power output of your amp at 2 Ohm? it should be around 120watts RMS per channel, for you to get full advantage of the speakers.

It's about 150 rms X 2 @ 2 ohms ...
thanks for the help i got a better understanding of it now

XC-C30 · 10-25-2006, 06:03 PM

wire the front and rear speakers together, and you should be alright. but be sure to set your gains right, cause you're overpowering your speakers, which could lead to blowing them in the end, if you're not carefull

korek28 · 10-26-2006, 02:51 AM

Ok here is what I've figured out so far with some help from some people from school. Seem right to you guys ?

Specs of AMP
- 75 W RMS x 2 @ 4 ohms
- 150 W RMS x 2 @ 2

Specs of Speakers
- 6-65 W RMS; 180 W Max
- impedence: 4 ohms

So if the above speakers are hooked up in parallel to one channel,
it would be 4 ohms in parellel with 4 ohms, making it 2 ohms.
( 4 || 4 = 2 )

Thus each channel would run @ 2 ohms, 150 W RMS per channel.

And thus since there is 2 speakers on 1 channel, 75 W RMS would go to each speaker.

Now is this correct ? Or am i making some mistakes here.

Sidewalksalvage · 10-26-2006, 02:59 AM

The amp is stable at 2ohms? Thats something important to check.

I believe if in series you would get half power to each speaker right?
But parallel will give equal power to each.

korek28 · 10-26-2006, 03:05 AM

Quote: Originally Posted by Sidewalksalvage

The amp is stable at 2ohms? Thats something important to check.

I believe if in series you would get half power to each speaker right?
But parallel will give equal power to each.

According to crutchfield.com it says that it is stable at 2 ohms....

not entirely sure on the parellel / serires part as to which one would give you half the power to each speaker... that is why i was asking.
how would i hook it up to get half power of each channel to each speaker?

DJiK · 10-26-2006, 03:45 AM

Quote: Originally Posted by korek28

not entirely sure on the parellel / serires part as to which one would give you half the power to each speaker... that is why i was asking.
how would i hook it up to get half power of each channel to each speaker?

Parallel & Series diagrams and resistance calculators --> http://www.the12volt.com/caraudio/boxcalcs.asp

It's true that a light bulb will be twice as dim when wired in series (vs. parallel), but I can't say the same about speakers.

monkeyc · 10-28-2006, 10:56 PM

The answer is: If you series the speakers, then you run each channel of the amp at 8ohms and you get half the effective power to each speaker but a cleaner sound since the THD (Total Harmonic Distortion) is decreased by ~half.

If you parallel them like you have indicated in the diagram above, then you will get twice the power out of the amp, but about twice the THD than if you just amped two speakers (one on each channel). This is a typical setup but I never recommend it since there will be a somewhat noticable difference in the sound because they are full range speakers. A two channel amp is capable of running more than just two speakers, but it is not designed to do so exlusively. So my question is WHY? Why are you going to have a two channel amp run four channels? That is what they design 4 channel amps for. You will lose your fader ability (which is a big factor in adjusting your staging) and you will gain unwanted noise.

I would do one of three things if it were me.

1. Return/sell the two channel amp and buy a four channel.

2. Forget about the rear speakers altogether and just amp the fronts. You want your staging to be coming from the front as if you were at a concert or at home infront of a TV. Rear speakers are just for rear fill and are almost unneccessary unless you have a 4.1 surround card or better.

3. Buy an additional 2 channel amp for the rears.

korek28 · 10-31-2006, 01:01 AM

monkeyc,
Yea I actually was thinking recently that it would be better to go with 4-channel amp over the 2-channel amp as it would make things alot simpler for me.

Now here's my new question: Already having a 2-channel amp, is it beneficial to sell this one and purchase a 4-channel amp, or is there no real difference if i run two 2-channel amps, one for the fronts and one for the rears??

Sidewalksalvage · 10-31-2006, 01:18 AM

Depends on power... sometimes you can get more power with two 2ch amps.

I suggest maybe getting a slightly more powerful amp for the front speakers so that you have crisp sound in the front and good fill from the rear

Overall there is no difference between a 4ch and a dual 2ch system when properly set up.

Shadow · 10-31-2006, 07:49 AM

Why not unplug the rear speakers?

Sidewalksalvage · 10-31-2006, 08:08 AM

Cuz thats just depressing....

But if you have an HU, you could run the front off the amp and the rear off the HU...

LaxPlaya8513 · 10-31-2006, 10:02 AM

but rear fill = annoying. Your diagram above is correct, wiring 2 4ohm drivers in parallel will lower the resistance in half to 2ohms per channel. As long as your amp is capable of running 2ohm leads per side you'll be fine. Alot of 2ch amps now a days are stable to 2 ohms. The only downside from this setup is the fact you lose the fading capabilities which many people really don't care for all that much anyhow.

BenOBS · 10-31-2006, 01:09 PM

Dont forget the sound quality downside...

Get a second 2 channel or get a 4 channels... Your carpc will allow you to setup the rear fill right...

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