How to kill drone

[Topless]

Ok, the exhaust drone in my convertible is getting to me on road trips. I need help with where to start. Does anyone have an idea of where the worst of the drone is coming from? Storage/trunk area, behind or under seats, floorboards?

I do not want to change the exhaust. Performance is better, and everyone says it is one of the best sounding C4 they have ever heard (Corsa owners even like mine better). I just don't get to hear it on the inside due to drone.

I have some Dynaplate to start working with, so suggestions would be appreciated.

thanks-

 

[G Winter]

I have a 90 vert with throaty exhaust. I am not so sure the drone don't come over the back instead of through the floor.

Glenn

 

[vetteoz]

I am not so sure the drone don't come over the back instead of through the floor.

It is more to with the harmonics of the exhaust; certain exh systems resonate at certain rev ranges.

 

[Schrade]

It is more to with the harmonics of the exhaust; certain exh systems resonate at certain rev ranges.

That's a perfect answer.

Early c4 had a short range of rpms in each gear, that sympathetic vibration occured in opposing sections of exhaust. The wavelength 'period' in 2 sections of exhaust at some point (rpm's) MULTIPLIES the sound, not ADDS TO the sound.

Interestingly (and NOT co-incidently) the INVERSE principle does the same thing. 2 sound sources with the OPPOSITE period, but still the same wavelength, played at the same time near each other, will make both their sounds 'invisible' to the ear. Turn one off, you'll instantly hear the other. With both sounds 'on', you won't hear anything, even with your ear right next to the sound. All you'll hear is air moving at your ear!

Know how Bose speakers work? You do now...

 

[Topless]

ok, but short of trying to install an inverse sound generation device, other solutions?

If frequency and amplitude are effected by the density of the material through which the sound wave passes, how and where do I make this change to alter the sound wave and make it less annoying?

 

[dogfish246]

What exhaust do you have?

I think your best bet is some type of sound insulation like the Dynomat or other brands... Take up all of the carpet and take out the seats, then lay the stuff down...

I cannot think of any other way to lessen the drone...
:cool

 

[bucket]

Ok, the exhaust drone in my convertible is getting to me on road trips. I need help with where to start. Does anyone have an idea of where the worst of the drone is coming from? Storage/trunk area, behind or under seats, floorboards?

I do not want to change the exhaust. Performance is better, and everyone says it is one of the best sounding C4 they have ever heard (Corsa owners even like mine better). I just don't get to hear it on the inside due to drone.

I have some Dynaplate to start working with, so suggestions would be appreciated.

thanks-

i always just crank the radio

 

[damoroso]

Actually, I believe your best bet is to have an X pipe put in the system to connect the two sides. This takes care of the resonance from the two sides working to multiply the sound. At least it works in C3's!!

 

[Topless]

I have a custom built 3" cat-back exhaust, with x-pipe and no mufflers.

Anyone applied stuff like dynamat and been happy? Did you do the entire interior? I would rather not for cost and weight, but if I have to...

 

[Schrade]

Actually, I believe your best bet is to have an X pipe put in the system to connect the two sides. This takes care of the resonance from the two sides working to multiply the sound. At least it works in C3's!!

This will work. But sometimes, you can change the 'period', simply by attaching firmly another piece of metal, or maybe another hanger to one side of the exhaust.

For instance, heat shields on imports often come loose, and vibrate in sync with the exhaust at the same rpm in each gear. A little piece of aluminum, and all it takes for THEM could be a sheet metal screw screwed into the shield to change the 'period'.

Experiment a little with some stuff that's 'invasive', maybe like some HEAVY hose clamps...

edit:
... NOT invasive...

 

[Topless]

Interesting. I had not thought of, or heard of that technique. I will give it a go.

 

[lefoy84]

You don't want drone but you don't want to change the exhaust or soundproof the whole interior. Good luck!

I have a custom built 3" cat-back exhaust, with x-pipe and no mufflers.

Anyone applied stuff like dynamat and been happy? Did you do the entire interior? I would rather not for cost and weight, but if I have to...

 

[Topless]

You don't want drone but you don't want to change the exhaust or soundproof the whole interior. Good luck!

I said if I have to. I don't want to put a bunch of weighty sound blocking material in the car if it is not going to work. What is the point of that?

 

[6 Shooter]

Topless - I'd say proper exhaust selection!

Later . . . . . .
6 Shooter

 

[vetteoz]

ok, but short of trying to install an inverse sound generation device, other solutions?

Change your diff gears so you are in a different rev range when cruising .I have a set range where resonance is bad; above or below that it does not \resonate

I have a custom built 3" cat-back exhaust, with x-pipe and no mufflers.

Anytime I have run with no mufflers I have had bad resonance at a certain rev range and popping when on throttle over run.

 

[dogfish246]

How heavy is dynomat?

 

[Schrade]

Not real heavy... unless you're starting out with a plastic car already... Then there's expense, work, pretty soon it's not just a little extra weight, but a lot more yup.

 

[Curious George]

Topless - I'd say proper exhaust selection!

Later . . . . . .
6 Shooter

"Proper" is a relative term... but I would have to agree. I redid my OE 1992 exhaust by taking out the center resonator (after the cats and before the rear mufflers) with a bolt-on section from Supernatural Performance and reused the OE mufflers and it sounds great. Same OE tone, just a little louder and no drone. At WOT it has a bite, but as soon as you are in "cruise" mode, it is very quiet (similar to a Corsa system). Those OE mufflers kill any tendency to resonate and they are fairly free flowing.

CG

 

[93Rubie]

You have drone? My exhaust set up is similar...mine is stock pipes all the way except for the muffler eliminators out back and an X pipe in place of the resonator. I don't have any noticeable droning problems. Then again my car is a coupe. If you have an x pipe already then that should have gotten rid of most of it. Why did you go to a 3" exhaust??? I put in what I have for less than 400 bucks. A stock LT1 doesn't need 3", the 2 3/4" is PLENTY big enough.

Solution is: to deal with it, or put mufflers on it.

Headers with NO CATS would get rid of the drone, you just might go deaf too...

 

[John Robinson]

Try this

On my 93 I found the bracket that holds the back of the muffler had become loose and allowed the mufflers to have excessive movement that caused a drumming noise inside the car. I tightened the bracket up and removed a lot of the noise. Second try adding some extensions on the tips of the pipes to move the sound further back from being directly under the car.