Drone/buffeting after soundproofing my trunk ?

[Vigilant 0]

Hi need help from you guys who understands soundproofing and noise better.

I've recently soundproofed the trunk and the floor pan of my VW passat. Used CAE equivalent of dynamat, CAE VB4.5 , 3M thinsulate. 

Firstly the road noise "seemed" louder but I'm guessing it is because I've brought the whole noise floor down too much and therefore accentuating road noise further.

Secondly there seems to be pressure building up my ears and it's causing minor irritation whenever I drive. My guess is the deadening lowered the resonant frequency of the car panels too much causing it to resonate and drone. The drone is quite low frequency and it is not very audible. You can feel the difference if you turn on and off the engine of the car at idle but it is not heard, more "felt". 

Has anyone has this problem before?

I thought it was the problem of my ears so i drove my wife's prius. The prius is noisier of course, but the cabin feels more "airy" and less "pressurized" and doesn't have that feeling that i have.

 

 

[Rudeboy 152]

How much vibration damper did you use? Did you cover the trunk vents? I had this happen once when I used way too much vibration damper during my first attempt at quieting a Civic. Put down multiple layers in the trunk. This changed the geometry and mass of the panels that make up trunk floor, moving its resonant frequency into a problematic range. I actually managed to create exhaust drone in a stock Honda Civic

[Vigilant 0]

4 hours ago, Rudeboy said:

How much vibration damper did you use? Did you cover the trunk vents? I had this happen once when I used way too much vibration damper during my first attempt at quieting a Civic. Put down multiple layers in the trunk. This changed the geometry and mass of the panels that make up trunk floor, moving its resonant frequency into a problematic range. I actually managed to create exhaust drone in a stock Honda Civic

Just one layer, however the passat already came with a lot of "stock" vibration damper. It's pretty well deadened stock I guess. No the trunk vents were not closed. On hindsight I think I should have not place too much damping on the centre of the trunk where  the exhaust pipe flows, especially when it already comes with stock vibration damper.

Did you manage to solve it? Did you remove the vibration damper from the trunk?  I'm thinking of trying to play around with how the spare tyre is mounted in an attempt to change the resonant frequency of the panels.

Edited October 26, 2016 by Vigilant

[Rudeboy 152]

10 minutes ago, Vigilant said:

Just one layer, however the passat already came with a lot of "stock" vibration damper. It's pretty well deadened stock I guess. On hindsight I think I should have not place too much  damping on the centre of the trunk where  the exhaust pipe flows.

Did you manage to solve it? Did you remove the vibration damper from the trunk?  I'm thinking of trying to play around with how the spare tyre is mounted in an attempt to change the resonant frequency of the panels.

Yes, I ripped it all out, added a little bit back to the bare sheet metal areas and covered the entire thing with CCF and MLV. Now that I think about it, Aaron helped me pull the vibration damper out It was all part of the process of learning how to treat a vehicle properly.

Spare tire wells are probably the most over treated vehicle areas. People pull the spare out, tap on the sheet metal and hear how flimsy it is and start adding layers, not realizing that the spare itself is part of the NVH system.

[///M5 2,833]

On 10/26/2016 at 9:05 AM, Rudeboy said:

not realizing that the spare itself is part of the NVH system.

Not just the spare, but everything in the car.  As some of you know, I do NVH measurements and consulting at pretty much all of the auto manufacturers and there is literally nothing in the car that is not both part of the analytical modeling of acoustic performance as well as of course the physical test and implementation.  The newer the car the more complex this is as the manufacturers lightweight the vehicles it is forcing them to relearn NVH all over again.

[Second Skin 120]

The pressure you are experiencing in the ears is most likely because you covered up the trunk vents that should always be left open to relieve the pressure. 

[Billy Jack 145]

Yes sounds like you did a little to much. You have basically turned your car into a speaker box, more or less. Kind of like when exhaust manufacturers develop drone free systems, they don't want the pipes resonating the same as the car. Or at least that's how I always understood it. I know they put a small valve into the pipe, to let out just enough volume, to expel the gasses without full volume resonating. Then at full volume, it opens 100%. What you have done, is basically seal it up so tight all the sound is trapped. 

Edited October 28, 2016 by Billy Jack