Harley wrote:
So far, the plan consists of:
-Second muffler
-dynamat on the inside of the firewall, and in the footwell areas
-more dynamat against the rear seat, and in the rear 1/4 panels
-carpet underlay or some kind (currently running none)
All good strategies. A second 'muffler' will help a lot, as will new door and window rubbers.
I used dynamat extreme on the entire floorpan, and firewall, and a thicker layer of dynamat Extremeliner on the firewall and front footwells.
I would also use a 'blanking plate' or similar to cover the speedo hole from the engine bay, then cover this whole area with dynamat as well. This is where you get a lot of induction noise coming through.
The other areas to do are inside the doors, inside the rear quarter panels and the boot lid. & on the rear seat back. This won't be cheap.
Harley wrote:
The other thing is if I put dynamat on the rear seatback, and then (like most young whipper snappers con-sarn-it) want a subwoofer in the boot, will it cut a lot of the sound from it, making it a pointless install?
Dynamat reduces panel resonanance, and distortion. By applying dynamat to your car's panels you will reduce road noise and reduce vibrations to a minimum. (it might sound like there are more, but that is cos you can here them now

). The other great benefit is that you can have a large sub (if that's your thing) and it will sound
better. Cleaner, deeper and clearer. Effectively louder too, as it isn't competing against as much road noise.
If you are going to install it in the boot, some other things to consider;
1) You need to have a bass port into the 'cabin' to make it effective, dynamat or no dynamat.
2) You will have a lot of panel resonance from the fuel tank and boot lid, rear parcel shelf etc, so more dynamat will be needed.
3) No more room for luggage
Hope this helps, and get the stuff off ebay, best price in Aust. Here is the link to the dynamat site:
http://www.dynamat.com/products_car_audio_introduction.html
Here is a link to what's on ebay now:
Cheers
Matt
http://search.ebay.com.au/search/search.dll?sofocus=bs&sbrftog=1&dfsp=1&from=R10&_trksid=m37&satitle=dynamat&sacat=-1%26catref%3DC6&sargn=-1%26saslc%3D2&sadis=200&fpos=4370&sabfmts=1&fobfmt=1&saobfmts=insif&ga10244=10425&ftrt=1&ftrv=1&saprclo=&saprchi=&fsop=1%26fsoo%3D1