4 Channel amp and some speaker options

[JungleGym]

So I'm having some trouble.

I'm thinking about getting some Crescendo PWX 6.5" and FT1 Tweeters to replace my Alpine SPR-60s in the front.

I have a PPI P900.4 amp. Precision Power PPI P900.4 (p9004) 4-Channel Phantom Car Amplifier

If I want to keep my rear speakers amped, would I need a passive crossover? If so, what's a decent one to use?

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[admobass]

What speakers do you use in the back? You could always run the front 2 channels at 2 ohms and leaving the rear at 4 ohms. Meaning connecting the new woofers and tweeters together to make a 2 ohm load on either side L+R. I would just forget the back and run the amp on just the tweeters and the woofers upfront.

 

[JungleGym]

I have Alpine Type R SPR-60 Coaxials in the rear.

 

[maylar 10+ year member]

As a minimum you will need a hipass filter for the tweeters. It seems they have a ready made one for those:

Crossovers - FT1 Crossover - Crescendo Audio | Online Store

The mids will roll off on the high end naturally, but if you want to control where they stop you'll need a low pass for them as well.