Car Stereos

Hey guys, any one know anything about car stereos and amplifiers?

Heres the thing. My niece has a 2007 corolla with a horrible stock system.
So, for Christmas I got her a Kenwood double DIN head unit so she has USB, Blutooth and hands free calling from it with her Iphone. Shes wanted something like this a long time.

But I seen no point doing the head unit when her speakers are so bad. So I decided to upgrade them as well, and add a proper amplifier to power them properly.


The amp is a Rockford Prime 250x4 (40W RMSx4)

Door speakers are Rockford Primes 6.75" at 4ohm. Doors are shallow mount so very limited as to what will work in there.

The rear deck Speakers are Infinity 6x9s.

After looking closer, its odd the way its worded. The Infinitys are technically 2 ohm, but by using the factory wiring etc.. it makes a true 4 ohm speaker, or the amp sees them as 4ohm.
But I will not be using the thin factory speaker wire, and running new 16g wire directly from the speakers to the amp for them, so lets assume they come out as being seen as 2ohm.

So my question is, will the amp have issues with a 4ohm load on the front channels, and a 2 Ohm load on the rear channels?

For what its worth, Rockfords says the amp will run 2ohm no issue.
More specifically they say: 40Wx4 RMS @ 4 Ohm 60Wx4 RMS @ 2Ohm or 125W RMS x2 Bridged @4Ohm

But unlear on the 4ohm front 2 Ohm rear question.

Wow, it has been a long time since I thought about this stuff! So most of this is from (aging) memory.

I believe there would be no problem to the amp. It will just send output down the wires as fast as the wires will take it, so to speak.
The problem is usually with the speakers, but going in the other direction, with higher ohm speakers getting blown out by being overpowered. Should not be an issue with low ohm speakers.
There may be some balancing to do. The 2 ohm speakers will have a different volume than the 4 ohm speakers, but there is a dial for that!
The thicker wire has less resistance (ohms) than thinner wire so that is a good call to attempt to get the full signal to the 2ohm speakers.

Hope that helps.

Not done any auto audio for a while but is it possible to simply add a 2 Ohm resistor into the feed for the rear speakers and balance the loads that way?

I'm not sure about the resistor but a good idea if needed.

I've been trying to do research and all I've come up with is that many cheaper amps will have issues and cut out or clip from it. mainly because the Advertised wattages/stable loads are not accurate.
But any decent, reputable amp should handle it without issue, and that even Rockfords cheaper entry level amps ( AKA the Prime I got) are decent amps and should be OK.

But I think thats referring mostly to just the 4 or 2 ohm load, not mixing them.

I'm also really confused on the Infinity speakers. 2 ohm, but seen as 4ohm ... which is it LOL.


I think power-wise Im good to go. Doing the smallest of the bunch 75-150% formula thing.
It comes out being 33-49W RMS should be the ideal power for the system. 40x4 should be good I hope.

Those door speakers are rated 45W RMS.

The rear say 100W RMS, but if truly at 2OHM, they should be getting 60.. right?

As speakers are basically wired in parallel across the amp two four Ohm speakers will give a total load of two Ohms - Ohms Law 101 lol - er I think :)

LOL. I think thats how it works. But gets confusing.

Ok, I found the answer. So for anyone else who may be curious:

That Amp will have no issues doing 4 Ohm front, 2 Ohm rear. Apparently the front and rear channels are independent.
But, the amp will output 40w RMS to the front and 60w RMS to the rear, so gain adjustments will be needed to balance everything out.

You just don't want to do something like Left Front @4 ohm & Right Front @ 2 ohm. May be issues there.
But same front and same rear is OK, so long as the amp will drive the speakers stable at that resistance. And this one is 4 and 2 Ohm stable so Im OK.

Yep you can always and most people do use the fader to equalize between the front and back speakers to their liking :)
Nice gift

Well shes 16. I have a feeling once the initial excitement goes away actual sound quality will not be a concern for her, but rather How loud will this thing go ... and start turning knobs/...
At least that was me at 16 with my car and stereo.

maybe if I hide the amp somewhere she won't be able to mess with it ... hmm.

That's a good idea