Aftermarket audio, basic?

Headunit - Basically two main options:
1. Replace factory CD player with a double DIN and use an adapter kit
2. Do a stealth install which replaces the small storage "pocket" just below the stock CD player. If you're parked in a shady area, you just close the door and the stereo looks completely stock. This is what I have.

Amps: If I was going to do an amp for the 4 speakers, I'd place it in the top glovebox (if small enough - might size amp specifically to fit in glove box) and then run wires from the headunit to the factory speaker wires. The sub amp I would always locate in the trunk, near the battery. Mine is attached underneath my sub enclosure

Doors: I got 4'x8' piece of hardboard from Home Depot for ~$5 and Noico sound dampening (best bang for $$$) off Amazon. Cut out pieces of hardboard and then 1-1.5" strips of noise dampening to seal around the hardboard and gaps (after applying sound deadening material to inside of doors). Sealing the doors will improve the bass response of the speakers and reduces road noise.

My setup is an aftermarket headunit, passive crossovers with aftermarket tweeters and woofers in the front, aftermarkets in the rears, and 2 10" subs in the trunk with an amp.

Here are pics of how I treated my doors, and custom sub box:

Kevin_Denver Trunk Subwoofer Enclosure by Kevin_Denver posted Apr 29, 2016 at 1:38 PM

 

Nice! My front speaker setup is completely custom, using parts from parts express:
Tweeters: Peerless by Tymphany OC25SC65-04 1" Textile Dome Tweeter
Woofers: Dayton Audio RS180-4 7" Reference Woofer 4 Ohm
Crossovers: Dayton Audio XO2W-2.5K 2-Way Speaker Crossover 2,500 Hz

I have a 5 ohm resistor on the driver's side tweeter and a 3 ohm resistor on the passenger's side tweeter. The original plan was 4 ohms on each side to match the tweeter to the woofers and crossovers, but this helps with balance for the driver's listening position (passenger's side tweeter is 1.5-2db louder). Adjusting the balance on my headunit even one position is too much.

The crossovers were kind of PITA to mount - had to cut away yellow insulation in the door panels to make space for them. Tweeters were very easy - only a tiny bit of cutting required.

I'm extremely happy with this setup - the quality is better than I think I could have gotten from an aftermarket component kit.

Next steps for me would be:
1. Cut out some of the speaker grills, especially on the front woofers. The sound quality on the car is noticeably better when the interior door panels are removed. The grills are quite restrictive, so I believe there's some blocking in the 1000-2500Hz range. I'd love to replace them with cloth, but would mean cutting the door panels and so far I haven't been willing to risk it.
2. Multi-band equalization. I can hear some peaks/valleys in the response, especially above 3KHz. An equalizer routed to a 4 channel amp would help.

 

A DSP would be amazing! I hadn't thought of programming a DSP for use in car audio - thought I would need to have an analog equalizer. I've been a hobbyist music producer for years, so I'd definitely be able to take advantage of all of the features. Would be a major increase in cost though as my current setup is ~$300 total (headunit and subwoofer enclosure materials were free).

The 7" woofers weren't any more difficult to mount than 6.5" woofers would be. If you look in my pic above, you can see I cut pieces of plywood to fit the factory location in the rear doors (mount and size of hole is same in front doors). The Prius factory speakers are built into the mount, so any aftermarket speakers require new mounts. When the windows are rolled all of the way down, they do just barely hit the back of the speakers with a clunk when rolled all of the way down. I've understood that others have fit 7" woofers in the rear without any clearance issues at all. I could probably get rid of the clunk by using a slightly thicker piece of wood for the mounts.

 

Great car, and it sounds like its going to have great sound! Enjoy the ride.

 

Post pics of your install! Would love to see what you come up with, especially if you mount those midranges.