collyn

Mine did that before the roof treatment. (The Snap-On guy said the car was designed to flex like that a few times over the course of it's life....and I was aging the car about 50 years worth with each bass note...LOL) So...I Took 3/4" mdf and cut strips about 6"x18-20"'s. I made them to fit the contour or the outer roof sections between the two center roof supports. I glued them in place with a medium thick layer of 100% silicon sealer then I went over them with two solid layers of Dynamat Xtreme. This serves two purposes, first it is really effective at vibration cancelling and helps db a LOT, second, it gives me a place to screw the upper winsheild/roof console that is being built into place. I also drilled 1/2" holes in the rear side doors inner "glass" metal panels and injected a milkshake mix of fiberglass resin, MEKP, and fiberglass reinforced body filler. I did this in all areas that were sandwiched between metal and not accessable for normal treatments. I then did a few more layers of Xtreme. The HHR has 6 master packs in it now along with Dynaliner on the floors and wheelwells. The exterior and interior are about 90% noise free at level's above 150 or so. Vibrational energy is spl wasted, so I wanted to eliminate all of the body flex possible. with in reason...LOL...no cement. The car is very quiet now at speeds up to 80 with wind noise from the front door seals the only noise source.

As far as the pressures and the reality of the numbers. I have built cars for db Drags one woofer class that hit 153-156. I had a '99 Honda civic hatch with one Memphis Audio Mojo 12 and two Memphis 1000d's in a 4.5 cu.ft box tuned to 55 hz. It was loud and aweful sounding but, it hit 150's easily. Oh...it had a stock alternator, no dynamat, no cap, and one Optima battery. So....before people say it is not possible....It is

I hope my modifications don't upset the HHR purists...haha...
I love the car and bought the HHR solely for this purpose. It is also not a daily driver at all. I have had the car since October of last year and the car now has 800 miles +/- on the ODO. It is at the store I work at mostly and if anyone in Dallas would like to see it in person I am at Cartoys in Duncanville, Texas...just off I-20 at Wheatland.

Ed RazorLite

Now an HHR block party sounds sweet.

I know what you mean by wanting it to sound good, thats why I keep this setup in my car, its one of the best sounding cars I have ever built. I love being able to play 20 hz and all types of drum music with it sounding clean. Even without deadener these cars dont make much noise. The worst part was the liscense plate and the roof racks. I believe the HHR utilizes quiet steel but I am not too sure.

I think the HHR was built for customization, so we are the real purists for wanting to enjoy all this car has to offer. And your install proves how good the HHR can look when you put it in the hands of a good customizer.

ProjectX

The audio in both of these HHRs is awesome, all i want is a pair or even three 12s, lol.