Scorvus

I want to add a subwoofer to the stock radio (because of the navigation). I was told I had to have the existing stock sub and add one with it's own control. When it comes to subwoofers, what should I look for. I don't really like thumping, just a good kick. If it could thump, it be nice, I have buddies who listen to rap. Is RMS wattage important? I notice cheap subs have low RMS even if the peak can be high. I want the cleanest bass possible, I'd spend around 300-400 bucks installed.

DeX

I don't understand......because of the navigation?
Who told you this? And which kind of car do you have with a stock subwoofer?
Nothing really......get something with a dual voice coil, strong surround material and RMS wattage equal to that of your amplifier.
You just contradicted yourself, do you want thump or no?
These are likely a crappy Xplod or other cheap brand, your sub hits peak wattage for about 1% of your song's duration so it's not really useful for determining an audio level, but it is important for what it can handle when it has to. What you want is RMS so you know what the wattage will be for a more constant portion of your media. Match the RMS wattage with your amplifier.
Then you should be hooking it to a class D amplifier and stay away from 2/4/1000000 subs in your trunk, you just need one.
I'll install it for you for $10. Hell, I'll write out the steps for you...
a) screw subwoofer into box
b) place box in trunk
c) run wire from amplifier to subwoofer
d) crank it up

As you can see, I've totally ignored the explanation of how important an amplifier is to your install and the reason for that is because you're completely ignored it in your question. The subwoofer is not nearly as important as your amplifier, just the same as the components in your computer are not going to be the same with a crappy power supply powering them. You need a good quality, stable RMS, class D amplifier which will take care of your $300 installed offer. Then squeeze a subwoofer into your budget and you're done. I paid $1000 for my subwoofer setup in 2001 and up until last year when I got drunk and fried the amp, I was still using it. And I am still using the subwoofer today. You're also going to want one with a remote gain **** so you can turn the intensity of the amplifier up and down from the driver's seat.....since there's no subwoofer control built into the stock radio. Good luck.

Scorvus

I don't have any tools to install anything.

2008 civic si, comes with navigation (don't want to replace this), comes with stock subwoofer (want to replace this). Thump is ok, so I guess I'll want a sub that could thump, but set lower for my tastes.

Went to a stereo shop, they said they could install a 500 watt RMS 10'' JBL sub in box with 600 watt amp in my car for about 500 bucks. Seems like a good deal, Im going to check other stereo shops to compare.

DeX

Tools needed for install:

- 9mm socket and socket wrench to remove negative battery terminal
- phillips screwdriver
- allan keys
- maybe a drill

That's it. You can pay for the install if you want but if you're in the northeast, come by and I'll do it for you.