Anyone else run into really bad exhaust drone?

[Turbo]

Originally Posted by sid94

I have an Hks legamax on at the moment and car pretty much sounds like stock until you get on it. Wishing I never got rid of my N1 lol


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What kind of front pipe are you running with it? Is it by chance the HKS resonated one?

[Ultramaroon]

Originally Posted by Turbo

I did stuff a pile of fiberglass insulation in the trunk under the removable floor. I was very surprised it did not seem to change things much - but I will try your suggestion to help understand the situation better.


Do you think covering the tire well in dynamat will help with this? And a little or a lot? I will be changing to a higher quality cat-back, but curious if this would/could improve things further.

I bought a used Berk muffler delete for funzies and experimented then. I have an Ace Laguna 90 now so, even though I still feel it a tiny bit, I lost interest in the project. My next step would have been to add mass to the well in some reversible manner. Sandbags or the like.

[ShansBRZ]

Dynamat didn’t do a thing to help with the drone in my car. I did the entire trunk and under the rear seats as well as the wheel wells and the walls behind the backseat side panels. I also put a layer of 1/2 inch sound deadening foam under the cargo mat in the trunk. Still drones like an SOB.

[Ultramaroon]

There you go.


I'm still convinced that it has something to do with the trunk but I'm not about to stuff it full of pillows.

[Ultramaroon]

Originally Posted by guybo

If you want to try something that is less expansive than getting a whole new exhaust, talk to a local exhaust shop and see if they can fab a custom helmholtz chamber for you. Look around online you can find a lot of info about size

Isn't a Helmholtz chamber more expansive?

[GrabTheWheel]

Stock muffler with a cutout. Best of both worlds

[Turbo]

Originally Posted by ShansBRZ

Dynamat didn’t do a thing to help with the drone in my car. I did the entire trunk and under the rear seats as well as the wheel wells and the walls behind the backseat side panels. I also put a layer of 1/2 inch sound deadening foam under the cargo mat in the trunk. Still drones like an SOB.

What are you running for an exhaust system front-to-back, Shans?

Also - are you boosted?

[ShansBRZ]

Running ft86 catted header, stock over pipe and cat. Cat back is a manzo s2. Not boosted....yet.

[sid94]

Originally Posted by Turbo

What kind of front pipe are you running with it? Is it by chance the HKS resonated one?

Invidia catless non resonated

[Irace86.2.0]

Isn't drone usually a low frequency sound, and that is hard to eliminate with sound deadening or other materials because large-wave/low-frequency sounds emanate around and through structures better?

[Ultramaroon]

Originally Posted by Ultramaroon

Before you change anything, just to prove it to yourself, stuff your trunk full of pillows, blankets, whatever. I mean STUFF it.

Then go for a drive. The source of the excitation is the exhaust but the source of the drone (aka resonance, flutter) is that drum head of a spare tire well.

Originally Posted by Irace86.2.0

Isn't drone usually a low frequency sound, and that is hard to eliminate with sound deadening or other materials because large-wave/low-frequency sounds emanate around and through structures better?

I worded the above poorly. I intended to point to the spare tire well as the place where that specific low frequency is amplified and coupled directly into the cabin. It's not actually the source. Resonance happens at any frequency. Drone, as I understand it in this context, describes a specific infra-sonic band of resonance felt inside the cabin of the vehicle. Another example of drone is the sickening feeling that can come from exciting the resonant frequency of the whole cabin by opening only one window. The car becomes a giant flute. The resonant frequency is increased by opening another window the same way notes are changed in a flute. The flutter is eliminated because the rest of the soft shit in the cabin damps the system enough to keep it from ringing at that higher frequency.

Ideally, elimination of the excitation is the way to go. A bell will stay silent if it isn't struck. The problem with flutter/resonance is that if the system is well tuned to a specific frequency, it takes very little input to get a huge response.

I've read a bunch of drone threads and haven't responded because I'm missing a key piece of information which will either support or refute my argument. I need to get a decent recording of the drone as well as that of me tapping the spare tire well. Then I can compare the two with a spectrum analysis.

Now that I've mentioned it, I have to do it. Stay *cough* tuned.