are there any? besides the obviouse, an aftermarket resonator or a new muffler. i've had the 4in summit system for a few months now and the incab 'drone' is wearing thin, especially when towin the jeep, or with the windows down.... its too much. any quick fixes or tricks you guys know of? i was thinking of wrapping the muffler in a hightemp insulation or matting or somthing, not sure if that would work since im not sure where the drone is originating from. i remember hearing somthing a while back about attaching angle iron or rebar to the muffler but can't seem to locate that thread.

Just an idea...what about using that DynoMat (or whatever it's called) that stereo guys use to deaden outside sound? Use it in the floorpans and doors? Would that work?


Tom http://www.dieselplace.com/forum/smileys/Pig.gif

You need to change the resonance of the exhaust system itself. Putting cat back it will change it for sure as well changing muffler type too. Personally I like my cabs quite so my exhaust mods favor flow and quietness because the droning gets old real fast. The exit point of the exhaust tip and it total length can have a effect too.

not sure that dynomat stuff will hold up to the heat, mabey though. i dont even know if thats a feasable solution, its just somthing i thought of since it sounds like the resonance is coming from under the rear floorboards where the muffler is, as opposed to out the exhaust tip. almost sounds like a harmonic vibration, that needs dampening, not a loud exhaust. it sounds nothing like a strait pipe, it's way more annoying.

It was just an idea. I always wondered why no one ventured it before, now I know.


Tom http://www.dieselplace.com/forum/smileys/Pig.gif

not sure that dynomat stuff will hold up to the heat, mabey though. i dont even know if thats a feasable solution, its just somthing i thought of since it sounds like the resonance is coming from under the rear floorboards where the muffler is, as opposed to out the exhaust tip. almost sounds like a harmonic vibration, that needs dampening, not a loud exhaust. it sounds nothing like a strait pipe, it's way more annoying.

The whole system, 4inch pipe and all is resonating. Any changes in it length or diameter or muffler type with change its resonance.

sorry tom, i misread your post. (put the dynomat in the doors and floorboards, not on the exhaust... duhhttp://www.dieselplace.com/forum/smileys/HiHi.gif) that would help eliminate some of the outside sound to a degree, i would imagine. although i dont think it would get the results im looking for.

sorry tom, i misread your post. (put the dynomat in the doors and floorboards, not on the exhaust... duhhttp://www.dieselplace.com/forum/smileys/HiHi.gif) that would help eliminate some of the outside sound to a degree, i would imagine. although i dont think it would get the results im looking for.

I do not want to sound like a downer but dynomat on floors would have little effect because in effect your whole exhaust system is acting like a "antenna" of sorts to transmitt the soundwaves into the truck and the cab construction and design "traps" the sound and resonants with it as well. There is a lot of energy in the sound to disapate. For a good cure you must change the resonance nature of current system. There is no other real fix.Edited by: snoman

Seems to me that since the exhaust is isolated by the rubber mounts, the drone is a function of the vibrations from the cab floor and sides. If you used a sound deadening substance, it might help reduce the drone. Just my .02


Tom http://www.dieselplace.com/forum/smileys/Pig.gifEdited by: TheBac

Dynomat makes a big difference (actually I recommend RAAMat instead since it is high quality and cheaper (available on eBay and raamaudio.com).


Even if you just mat over the two vents in the back of the cab you will reduce exhaust and road noise substantially (anyone know what these vents are for?). Beyond that the rear wall of the cab and door skins seem to make the most difference. Deadening the floor helps, but not as much as it does on other vehicles since the factory insulation and carpet in our trucks is above average.

Thanks Joe, for the insight,


Those vents are for fresh air circulation in the cab. I don't recommend covering them. Am I correct in assuming that the potential is there then for any stray exhaust gasses to stay in the cab, not vent out?


Tom http://www.dieselplace.com/forum/smileys/Pig.gifEdited by: TheBac

Dynomat makes a big difference (actually I recommend RAAMat instead since it is high quality and cheaper (available on eBay and raamaudio.com).

To be its most effective, it need to be on the bottom of the floorboard not the top. You need to interupt the sound energy before it contacts the floorpan metal.

Thanks Joe, for the insight,


Those vents are for fresh air circulation in the cab. I don't recommend covering them. Am I correct in assuming that the potential is there then for any stray exhaust gasses to stay in the cab, not vent out?


Tom http://www.dieselplace.com/forum/smileys/Pig.gif





About the only way you are going to get exhaust gas in the cab is through those vents. An exhaust leak under the hood could send gasses through the firewall of course, but that would be a serious issue with or without the vents. Most likely, the vents are there to make it easier to close the doors (with the windows up), but there really isn't a noticeable difference even when they are covered.

What about wrapping the muffler with header tape?

I have two layers of Fatmat in my truck for my sound system, and yes it makes a big difference. This is a big job though. I thought those vents were to relieve in cab pressure when closing the doors.

I thought those vents were to relieve in cab pressure when closing the doors.

The real reason they are there is allow for positive cab ventilation

Well, I fired off an email to the owner of Raamat, a sound deadener company similar to DynaMat. Really nice guy, he offered this reply to my inquiry:
<DIV>Tom,</DIV>
<DIV> I appologize for keeping you waiting, I had an unexpected road trip that kept me away from a computer most of the weekend, just catching up now. Unfortunately an exhaust drone can be very difficult to remedy as my general install guide below will explain. Last year my son and I matted and used alot of Ensolite on my buddies F350 dual cab with very good results in controlling engine noise and heat, in fact hard to even hear the engine now but he did not get a drone with the Gates exhaust(chip, turbo, shift kit, etc as well) </DIV>
<DIV> Using any good mat product and Ensolite together would be the best course of action but they may have to add a resonater as well, wish it were otherwise.</DIV>
<DIV> </DIV>
<DIV>Sincerly,</DIV>
<DIV>Rick</DIV>
<DIV>RAAMaudio</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>


Ensolite MLC ® is an acoustical heat / cold insulator. This premium insulator was developed by NASA and used extensively in the space program and by aircraft manufacturers. It measures 1/8" thick by 6" wide.


This product may be used in conjunction with our Raammat.
It is exceptionally an effective acoustical absorber, being used throughout the car.


So it looks like the only way to treat the drone problem currently is a resonator plumbed into the exhaust or something similar. At least we're trying to figure it out.


Tom http://www.dieselplace.com/forum/smileys/smiley30.gif</DIV>

some good research there, ill prolly just end up with a new muffler from somewhere here in the near future.

Turn up the radio.

Get under the truck and bang on the exhaust to see if it rattles, etc. Is it
touching or rubbing anywhere? Look for signs of contact, ie. shiny spots.
ANY contact with the frame or truck other than the hangers is going to
transmit noise and vibrations into the cab. Get under the truck while
someone revs it a bit and see what it sounds like, and if there is any
visable extra movement. If it vibrates, grab ir with a gloved hand and see
if sound in truck changes. Try this all up and down the system.

Most times the resonation is coming from the exhaust hitting the back of the muffler and bouncing the sound waves or pressure waves. In a lot of conditions, a mass damper on the exhaust just forward of the muffler may help. Try hanging a pound of mass by an exhaust hanger just forward of the muffler. It may change the characteristics just enough to prevent the drone.


HTH,

You may even want to try replacing the muffler with a piece of straight pipe -- it really isn't *that* loud and it would likely eliminate your resonance issues.


With the radio turned up, I can't even hear my exhaust (or anything else other than music for that matter).

Try the hose clamping a weight to the exhust thing. IIRC some guys have good luck with clamping a peice of angle iron bout a foot or so long to thier pipe up by the motor. I also notice less resonance with my muffler removed than with it in. Resonace is a function of the muffler you have and of were the exhaust dumps. Unless I am nuts I also noticed a slight difference with a spray in bed liner added too. Mine is pretty thick and rubbery though. Sound deading material will help but I dont think its the best option. JMO

My '96 Caprice LT1 comes with a 2 pound(?) weight welded to the the exhaust (towards the front under the pass. side) for the purpose of eliminating exhaust resonance. Might be worth a try. Probably need something heavier than 2 pounds for a 4in" exhaust.
JP

Here is a resonator http://shop.airflowonline.com/Merchant2/merchant.mv?Screen=C (http://shop.airflowonline.com/Merchant2/merchant.mv?Screen=CTGY&amp;Store_Code=AFSI&amp;Category_C ode=R) TGY&amp;Store_Code=AFSI&amp;Category_Code=R that might work. I have considered getting one for my truck, but don't like the fact it isn't SS. The weight before the muffler is an interesting idea that I might play with. Some hose clamps could be used to temp somthing up to see if it will work.

You guys with the bar stock or weight ideas have got it right. We use stuff similar to this on submarines to reduce radiated noise signature. essentially what it boils down to is on any straight pipe, there will be thin slivers of bar stock (maybe 1/8" by 1/8") the length of the pipe, but there are enough strips to go around the entire pipe, then it is just band-clamped on. Let me tell you, this stuff works! Our submarines are the quietest in the world. . .


Dennis