New to the forum. I spent a few hours searching this topic and got a couple of different results that may or may not have been conflicting. Lots of excellent info here and I thank you.

I'm thinking of upgrading the speakers in my new roadster which has the stock 6 speaker system. I don't want add crossovers or amps, I just want to drop in better speakers for subtle but hopefully significant improvement in sound quality.

My questions are these.....

The two speakers in the door....should I replace the smaller one with a 3.5" speaker or a 4" speaker? The depth of course will also have to fit

The larger door speaker.....a 5.25" speaker or a 6.5" speaker?

I assume my roadster has 6x9's behind the seats and will take any replacement as long as they are not too deep.

Does anyone know how deep the replacement speakers can or can't be?

I'm looking closely at Infiniti "Reference X" series which has all the sizes I think I need. As far as I read all the stock speakers are 4 ohms. All the Reference X speakers are also 4 ohms

Thanks