Car stereo amp install fail and a question
 

The stock stereo in my 91 BMW 318is has been lacking in power and a weird static comes and goes.

So being the DIY self kind of guy I am, I order a 250 watt amplifier and four 5-1/4" speakers from crutchfield.

I pull out the center console, rear seat, under dash covers, trunk liners etc. in anticipation of getting it done right and running new speaker wires.

I mount the amplifier in the trunk on the back seat sheetmetal, run a ground and power wire and then notice a lack of speaker outputs!?!?

Turns out I bought an amp for a subwoofer. :(

I guess I'll have to buy a sub now to make use of my new amp. :)

Yes, I know I wasn't very observant, but I've never used or installed one before. Reading the directions after the fact didn't help.

That said, I'll get a 4 channel amp later, but have a question on the specifics: 2 ohm, 4 ohm, crossover, bridged, etc.

What am I reading? I just want the music a little louder and cleaner when a good song comes on, not a concert hall reproduction.

on the 4 channel amp- 2 or 4 OHM means the amplifier is capable of running either load- a 2 ohm load is typically harder on an amplifier as it has 1/2 the resistance of a 4 ohm amp. Virtually all 4 channels on the market today can run either load.

Since the goal is just to power 4 5.25" speakers, any 4 channel amp will do and IF you are using it with a subwoofer get one that has what they call a "high pass crossover"- that will sort the frequencies out so only mids / highs go to the smaller speakers.

Virtually every 5.25" speaker on the market is a 4 ohm variety so if you are simply plugging one speaker per channel on the amp then it's all going to run at a 4 ohm load. That's as simple and as perfect as it gets.

The subwoofer amp probably has a "low-pass crossover" in it- you activate that so it sends only low bass to the subwoofer.

Oh, and on your car notice that on your car it probably has a perforation exactly dead center in the sheetmetal that is behind the rear seat and separates the trunk- should be about the approximate size of the armrest in the back seat- it was designed to provide an opening for skis (assuming the car had the options)

Hit it with a hammer, and it comes out- then your bass is vented through into the cab.

I know your car well.

rjp

^^^ Thanks for the info.

When I pulled the seats and rear trunk liner, I noticed the pass through sheetmetal was already gone.

Reading some more, I think I'll add a piece of plywood to the trunk/seat back, cut a hole for the sub at the pass through and re-install the sub amp.