Sterling302

Hey everyone. Just purchased a Dynomax cat back system for my 2012 5.0. Install was easy and the sound is incredible. I had axle backs on it before, but wanted something more performance oriented. Both exhaust set ups (the axle backs were Pypes) droned really badly at 2k rpms. No more no less. Unfortunately, that is EXACTLY what I cruise at in 6th going down the interstate. Around town it's manageable, but on the interstate it's borderline undriveable. I sprayed some Boom mat spray on in the spare tire area, and it did help a LITTLE. But the thing is, I don't want to spend 200 dollars on Dynamat if it isn't what I need. Is the drone actual noise resonation in the cabin, or vibration? And how should I fix this? Thanks in advance.

Also note: Some may bring up the argument, "Why would you want to subject others to a sound you want to keep out?" And I can assure you it's not like that. The noise I'm dealing with in the cabin is not what others are dealing with on the road. The cabin noise can be likened to having your ear next to a sub woofer playing a constant note. Volume isn't the problem.

MrSandman

Sound is vibration.. so. yes, and yes. Bad drone is the result of your car effectively acting like a tuning fork. Padding, etc, cant get rid of it. It may change it a little... but it is still there. You can feel drone because your car is vibrating, albeit at a very low frequency.

Think of it this way.. Hold a piece of sheet metal next to a bass organ pipe. The sheet metal will vibrate as the sound (which is a vibration) hits it. At certain notes, however, it wont just vibrate at the same frequency. If the conditions are right, it will vibrate at a resonant frequency.. which may actually be more "intense" or higher amplitude than the frequency of the organ pipe.

http://en.wikipedia.org/wiki/Acoustic_resonance
This really is worth watching...really. You will know exactly what you are dealing with after this.


I think you will really relate to the sound he creates during the video... mind numbing. I had a mac axleback for a short time on my 07 v6.... I really do think it wouldn't have been safe for pregnant women.. seriously!

Adding resonators, or somehow changing the length of the exhaust system is the only way to help.. other than switching to something different.

Sterling302

Well my future exhaust plans include a set of long tube headers and shorty offroad x. I guess I should wait for that and fix the problem accordingly.

Ricardo

Long tubes will intensify the volume, especially with off road x. I had bullet style mufflers welded in staggered in front of the axle to work as resonators and it helped a lot.

Sterling302

Well the volume doesn't concern me as much as that awful low frequency vibration. How much of a damper did the bullet mufflers put on your exhaust note?

808muscle

Bullitt flow thru mufflers don't quiet the volume, they just cancel frequencies. I run two sets on my 06 GT. Blower, cams, longtubes, offload H, cherry bombs and Pypes m80s mid mounted before the over axle pipes then exits with SSS which are flow thru ones like a borla stingers. Still very loud deep idle and screams at WOT but no irritating drone.

Your options are new axle backs or weld in some resonators.

Sterling302

Thanks for all the help guys. I'm interested in the Bullit flow through muffler idea. I can't imagine it would cost too much to just have them welded into the exhaust? Either way I will be sure to let you guys know how it goes...Like I said I don't care about the volume really.

Ricardo

Good luck! Also sometimes I still tire of the volume and switch to stock axlebacks for a week. It helps to get a break from broadcasting to the world the position of my foot on the throttle pedal. lol You could do that to give yourself a small break.

Mathusula2

808 - could you perhaps post a picture a what you have going on in your exhaust?

Ricardo - how many inches are your mid-pipe mufflers staggered? I was thinking of doing just that with my exhaust (Flowmasters American Thunder), only I was going to stagger Pypes m80s given their small size.

Sterling302

I was looking at my build list today and noticed I had 4.10 gears on it. I didn't think about that. Wouldn't that elevate my 60-70 cruising rpm? In other words, wouldn't that be kind of a cop out to kind of deal with the noise longer until it inevitably puts me in an asylum? Since the drone is only bad at 2k and I'd be cruising at 2,400-2,700?