Has anyone just replaced the speakers and kept the stock head unit? I’m curious if that improves the sound?
I don't recall anyone talking about it - but that used to be the first "go to" solution going back a decade or 3.
I did this, but also had an aftermarket amp connected with the factory radio. This was on a 2018 Prius Prime without JBL. Swapped the factory head unit with an aftermarket one. Did this back and forth a couple of times. I couldn't get a good sound out of the factory head unit, although some have had the opposite result from what I've read. Curious if anyone has tested the frequency response on the factory deck.
If your car does not have the premium audio option, aftermarket speakers are a great upgrade. They will sound better even with the stock head unit. Even if you have the JBL option aftermarkets will sound better-still, but you have to replace more than the speakers to make it work. This makes the upgrade harder and more expensive, so I only recommend it for those with the regular system.
It depends on your ears. I’ve heard plenty of people comment that still enjoyed the stock setup. For a person that is use to good sounding systems, the stock head unit sets its own frequency gain/limiting to help protect the sound system so a user will still be constrain to the head unit if they keep the head unit. There is no equalizer so you can’t make fine adjustments. The speakers are very thin paper cones so they can’t take a large amount of wattage and at certain frequencies. They will get distorted very quickly when turning things up. The 3.5” has a really large capacitor on the speaker connector which filters out all of the bass and a bit more. I do recommend some sort of capacitor, but not as big as the stock one if you place in new 3.5” since you will get distortions when the music is playing loud low frequencies. My infinity references I replaced with comes with capacitors I can add on to install. The 6.5” surprisingly has strong bass but has a muddy sound and vocals aren’t as clear and bright. I can tell you that speakers are a good upgrade, but it will probably leave you wanting to do more if you are looking for more adjustments. If you do want to keep the stock head unit, you may want to look into the kicker key amp which will auto tune your sound so the head unit will be back leveled as well as allow for more power and less chance for distortion.