Critique my DIY in my 2K3 AV6

I was wondering if some of the more seasoned installers/DIY'ers would critique my setup that I did myself.  What I am experiencing is that low bass notes arrn't hitting like I expect them to.

US-Accoustics 2150, 12.1 Infinity Perfect, QLogic Type 1 (sealed).  I am feeding the amp the signal from the positive wire from the left/right rear speakers, using the high level input on the amp.  I grounded both the amp and the high level input to the same ground on the chassis infront of the spare tire well.  Something else was originally grounded to that bolt as well.  The amp is bridged to the subwoofer. 

I find that low bass notes arn't hitting, but more boomy notes do.  I wired both the power cable and remote turn on through the middle of the car between driver and passenger seat and underneath the carpet. 

Will I get a better sound quality if I use a LOF instead of the high level input?  I don't hear any alternator whine.  Any other input or comments for a first timer would be helpful.  

I'd say to set the amp's crossover frequency to around 100 Hz, the bass bosst to +6 db, and the gains by following these guidelines.  Also make sure the built-in crossover is set to Low-pass

The ideal setup would involve an aftermarket head unit with separate subwoofer preamp outputs, or at the very least one with RCA preouts.  These will always give you a cleaner signal than a high-level signal.

En external line output converter might give you a lil better SQ, plus it allows you to adjust the input level to the amp whereas the high-level inputs built in to most amps are fixed.

External line output converters usually work a little better than the ones that are built in to many amplifiers.  But depending on what kind of stereo is in the vehicle right now, the difference in SQ may or may not be very noticeable.

Of course, make sure the bass control for the stereo is not turned all the way down either, or else no bass will go to the speaker wires that you're tapping in to (and thus no bass will go to the amp or subs).

Woops.  I grounded the high level to the chassis/amp ground.  Should I instead connect that high level ground/negative to the rear left and right speakers negative/ground?  Or does it not matter?  If I remember correctly, the manual for the amp said nothing should be connected to the speakers negatives.

Yes, I did bridge the amp using the far right and far left connectors.

The US Acoustics manual says the following -

Connecting the High Level Inputs,  Low Power Head Units with common ground speaker outputs.  Purple Wire of USB Harness to LEFT +.  Brown Wire of USB Harness to RIGHT +.  (The wire is actually green, not brown.)  Black Wire of USB Harness to the CHASSIS GROUND of the head unit.  NOTE: Do not connect anything to the R - or L - terminals of the head unit.

Connecting the High Level Inputs,  Low Power Head Units with common ground speaker outputs.  Purple Wire of USB Harness to LEFT +.  Brown Wire of USB Harness to RIGHT +.  (The wire is actually green, not brown.)  Black Wire of USB Harness to the CHASSIS GROUND of the head unit.  NOTE: Do not connect anything to the R - or L - terminals of the head unit.

High Power Head Units with floating speaker outputs.  Purple Wire of USB Harness to LEFT +.  Brown Wire of USB Harness to RIGHT +.  (The wire is actually green, not brown.)  Black Wire of USB Harness to the CHASSIS of the head unit.  NOTE: Do not connect anything to the R - or L - terminals of the head unit.

So which head unit do I have, high or low power?  What is the difference between "CHASSIS GROUND" and "CHASSIS"?  Where is the best place to connect the USB Black wire for grounding purposes?  Thanks.

First off, if you have a "premium" factory system then you should use a line output converter designed specifically for that purpose--the ones built into the amps just won't work well with the factory amplified system.

Regardless of what kind of converter you use though, you'll still be tapping in to 4 factory speaker wires--a positive and negative for the left speaker, and a positive and negative for the right speaker.  Even though you're going to be bridging the amplifier, you still need to hook up all 4 of these speaker wires to the high-level inputs on the amp (or to the external line output converter if you're using one).

What stereo did the vehicle come with?  Also, what's the year/model/make/trim line, etc. of your vehicle?

I have a 2003 Honda Accord EX V6 with Navigation.  The deck is a 6 cd in dash changer.  I do not believe that there is an external factory amp, but it would still be considered amplified would it not?

Just so I am clear, based on what you are saying, it is bad that I grounded the high level input to the chassis, instead of connecting it to the left and right negative wires?

Take a look at a LOC I am probably going to buy.  http://www.soundgate.com/products/line-output/index.htm  I and soundgate have concluded that my setup is Type 1, so this agrees with by belief of no external factory amp. 

Your setup is a type 1 setup, but even vehicles with external factory amplifiers could do a type-1 setup.  All they mean when they say type 1 is that you're using a high-level (amplified) signal, as opposed to an unamplified, low-level RCA type signal.

Many vehicles that have separate external factory amplifiers, use head units that only output low-level signals.  Some output a standard signal that you can technically hook straight up to an amp's rca plugs (provided you solder on plugs to the wires).  Most however (including the bose systems) use a differential type signal that requires a special converter such as the soundgate converter.  A standard line output converter (as well as the line ouput converter built in to an amplifier) will not always work properly.

To answer your question about grounding the high level input...you should hook up both a positive and a negative coming from each speaker.  So if it's a 2-channel line output converter, you'll hook up the positive and negative for the left channel to the positive and negative speaker wires going to the left speaker you're tapping in to, and then the positive and negative for the right channel to the positive and negative speaker wires going to the right speaker you're tapping in to.

When they say "common ground" they're talking about  the systems used primarily in older vehicles, where each speaker does not have its own positive and negative wire.  Instead, the front speakers will share a single negative wire and the back speakers will share a single negative wire.  In reality this "wire" is often basically the vehicle's chassis.  I don't know if them talking about the common ground stuff might have been what threw you off but hopefully that helps a bit.

Each speaker in this vehicle definitely has its own positive and negative speaker wire, so for a typical 4-channel system there will be 8 total speaker wires.  For your purposes only 4 of those wires will need to be used when you hook up a line output converter like the soundgate model.