My Cargraphic was mount with what you said, hose clamps. I still think it drones more than my liking.
Anyone has ever tried to throw lots of pillows on top of back area? Does it reduce any drone?

 

then it is the exhaust itself. I can't say whether the mounting system helped, but I can say that the crossover pipe and the headers did for sure, as I had it without either before and it droned as much as my fabspeed straight pipes with cats.

 

Geek Alert!

I think it's a fundamental resonance of the vehicle; the way to reduce it is through selective damping. What I was seeing was around 90 - 100 Hz (wavelength around 150"; interesting, isn't that the length of a 911). Factory exhaust does it really well but ends up sounding wussy.

If anyone can try a flexible rubber mount, it may help; i'd be worried about setting fire to something. The geek way of doing this is to feed an inverted sound-wave through the stereo system. Taking orders, who'd be interested...just kidding; MOD please don't ban me!

I may try it out installing the new stereo.

 

Hi, just to share with you what I did to significantly reduce exhaust drone on my car...

I have a Toyota Matrix XRS 2006 (Same engine than a Lotus Elise "2ZZ-GE") and a magnaflow catback exhaust.I was having a drone problem and the solution I've tried worked pretty well. I had a resonante frequeny around 130-150 hz when I was crussing at highway speed witch was getting annoying, especialy on long drives.

I'm not shure how this solution would work with your car but it could give you ideas.
I used Mineral wool wall insulation (5 1/2" thick) around the spare tire well and behind the rear side plastic trims. All that space was empty air witch would resonnate and tranfert sound inside the cabin and keep it there. With the insulation in place, sound wave are absorbed on there way in and out of the cabin resulting in lower noise.

In my car, the noise level was reduce by 5 dB SPL, witch is almost by half!

Result may vary alot from car to car though...

Here are the details and pics:

http://matrixowners.com/index.php?showtopic=87751

 

good info. Problem with our cars is lack of room and an already heavy azz.

 

I've always thought the drone is in part a vibration so sound proofing won't change it much.

 

I know, space most be tight in those cars but look around, any free air space between trims and body panels are a sound conductor and can be filed with insulation... Be shure not to block any vents though.

Actualy, drone is a resonant frequency... Noise from the exhaust amplifies itself at a certain frequency range. Every car, room, space has it's own resonant frequency.

 

Bottom line is: muffler components( how its made) and from what, OD tubing and overall design has a lot to do with resonance...
I have been playing a lot with my mufflers and various combinations there of...

 

The viper guys are big into vortex cones to reduce resonance......I installed a set into my Gen 1 fabspeeds and they reduced the resonance say 25-30%.

I think the best solution would be to stiffen up the way the exhaust is attached to the car, which would raise the resonant frequency out of the current cruising rpm (2300-2800 rpm).

I also wear noise reducing headphones some mornings (I leave the house at 6 AM).

 

I put back in some of my sound insulation that works, if you have 70MM why not try John D's noise reducing
Optional “Quiet” Sound Inserts for SpeedTech 996TT Exhaust
Optional removable insert to reduce sound. Installs at rear pipe (requires removal of tips) and lowers cabin volume of exhaust. Can be removed and re-used at any time. With this option you can have a quieter exhaust during the week and increase the volume for weekends, rallys, track days, etc.

Optional removable insert to reduce sound. Installs at rear pipe (requires removal of tips) and lowers cabin volume of exhaust. Can be removed and re-used at any time. With this option you can have a quieter exhaust during the week and increase the volume for weekends, rallys, track days, etc.

 

<how about injecting some liquid expanding insulation foam ?> that one can get from the DIY store ?

 

I'm not sure if expanding foam is a good idea, Fiberglass and mineral wool has much better sound absorption and resist heat up to 1100oF. Foam expand in every direction and may end up where you don't want it to, It's sticky like glue, it would be very difficult to remove if needed...

 

Did anyone try this on a 996TT?

 

yes, did not make any difference. Still have one roll left.

 

( I think " Small pieces in the ears would do ". )
I wrapped on exhaust. Did nothing.