Soundproofing a MKIV - How much of a difference?

Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
I just wanted to echo Wankel7's post about the wheel wells...

As you may remember, I was extremely disappointed with my soundproofing results, after the doors, door cards, and the rest of the entire interior from front to trunk was done. I was still seeing 78-80 db at 70mph on a quiet highway.

I recently finished up a big job on the wheel wells. I used "Noico 80 mil 36 sqft car Sound deadening mat" on the liners:

https://www.amazon.com/gp/product/B00URUIKAK/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

And I sprayed the wells using 3M 03584 Professional Grade Rubberized Undercoating - 16 oz.

https://www.amazon.com/gp/product/B002H9CMCQ/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

The Noico stuff is flexible enough even in a cold garage to work with, and cuts easily enough to fit the weird shapes of the liners.

I cleaned and scrubbed the wells then taped things off before spraying a full can of the 3M stuff on. I didn't tape off the screw holes, and just was careful to avoid covering them too much. This worked out fine. I didn't just spray the wells in the front, but also the longitudinal braces in the frame - what I could get - as I figured those too transmit noise back into the cabin.

The big struggle was to get the liners back in, as the tolerances had changed with the Noico stuff on them, but I got there. I only couldn't get at one screw in the rear left well, as I needed another pair of hands. Otherwise, they went back in well enough.

The result? Using a new decibel meter (my old one was no longer supported) on an iphone, on the same stretch of highway, I got 71-74 decibels, while my buddy's 2016 GTI read 70-73. That's a six decibel difference, folks, or four times less in sound pressure. I couldn't believe it, so I checked it again several days later and got the same result.

The car still transmits high frequency noises into the cabin, no doubt through the window glass, but otherwise, I'm pretty damned happy and there's more to come.
 

Rrusse11

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Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Judson,
So it sounds like, {;o), the best bang for the buck is to do the wheel wells. I've got a bit of a drone with my exhaust at 2k rpm that I doubt deadening the wells would fix. But when the weather gets better,
I'll give it a shot. BOOM to bang ehhhhh.
 

Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
Hey Rrusse11 -

I'm not certain that it's the best bang for the buck, but it sure seems that way. I think any car with very little soundproofing is going to transmit it one way or another. If one only does the wheel wells, then the sound may find its way through the floor and the doors.

I may do the wheel wells of my 04 Jeep Grand Cherokee first just to find out. It has surprisingly little soundproofing anywhere, and could use some quieting for sure.
 

kwong7

Veteran Member
Joined
Mar 25, 2004
Location
Southern Caifornia
TDI
2001 Golf GLS TDI / White
I came back from a 1K miles road-trip (roundtrip) and measured 80-93 decibels from speeds between 35-85mph. It was deafening. It turns out my original rear wheel bearings were toast. Best $250 I spent. I thought all that droning noise was coming from my new tires.
 

turbovan+tdi

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Joined
Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
Agreed, you can hear a lot noise thru the wheel wells. I partially did the fronts on my wagon and my wife's, but need to tackle the rear next.
 

Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
I removed the liners, sprayed on the 3M stuff onto the wheel well, then also lined the inside of the liners with the Noico stuff. So, once assembled I had a double-layer.
 

turbovan+tdi

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Joined
Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
Double check body plugs are installed. I've always had a lot of noise at my feet in the wet and snow-since I got the car almost 2 years ago, had it up in the air the other day and never really looked until now, missing both outer front body plugs-nice big air chamber right under my feet and directly in the path of rain/snow etc. Installed some and noticeable reduction in noise.
 

Judson

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Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
Just had a six-speed installed by Brandon at Metrick Methodz in Fort Collis. It a DRW code, with a PD150 DMF and Quaife courtesy of Darkside. RPMs @ 70=1800, @80=2200. I'd say overall decibels dropped about 1.5-2db, no more. Now at about 69-70db at 70mph, and 73db at 80mph. Yes, that's right: I saw a genuine 69db there.

At idle and around time and just standing next to the engine, it is very smooth, very quiet: a lot like the 2015 TDI I test drove recently.
 

jettamk4tdisd

New member
Joined
Oct 14, 2016
Location
Rapid City, SD
TDI
04 Jetta TDI 5sp
Judson - In post #23 you state that the door seals are bad and are next. I am curious if you replaced the felt seal that runs along the top of both the front and back doors or the individual seals for each door and if it made a significant difference. I'm running 85 to 90 most of the time between Rapid City and Gillette on I-90 and it seems like there is significant noise from the top of the driver and passenger's windows. I've adjusted the doors in as far as they go and that did make a big difference. I don't know which door seal to replace next.
 
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Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
A lot of my highway noise - what I thought was coming through the windows - was eliminated by soundproofing the wheel wells.

Now that The car is much quieter I can hear more little things and yes, I do have some missing felt and a tear in the front door seal that isn’t too bad but needs attention. My doors are also adjusted right up against the body and have been for maybe 10-15 years now.

Sorry I can’t provide more info on this. I have such a long list of things to do to the car (and it keeps growing) that addressing the seals is low priority right now.


Sent from my iPhone using Tapatalk
 

dremd

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Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
I never quite understood what parts you sound dampened.

The plastic wheel well liners?
The metal that the plastic attaches to?
Both?

I’m definitely considering doing the same, maybe to my EV’s as well.
 

Judson

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Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta

Jetta_Pilot

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Apr 14, 2005
Location
West Hill, Ont.
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2015 Passat Highline TDI Candy White (SEL Premium) long gone 2002 Jetta TDI
Judson,
So it sounds like, {;o), the best bang for the buck is to do the wheel wells. I've got a bit of a drone with my exhaust at 2k rpm that I doubt deadening the wells would fix. But when the weather gets better,
I'll give it a shot. BOOM to bang ehhhhh.
I'd almost bet that you have removed your muffler!
I had done that ( Mufflerectomy ) and had this droning. I eliminated it by installing a straight through muffler. Used to be called a Hollywood muffler.
 

Rrusse11

Veteran Member
Joined
Jan 23, 2014
Location
PA Deutsch Country
TDI
2002 Golf, 5spd; 05 Jeep CRD
Jetta Pilot,

Close, I went for a 2.5" catless exhaust, it does have a resonator/muffler
at the end, where the original used to sit. I've gotten used to it now,
it's only at 2000rpm, and tells me I need to downshift. {:eek:)
No problem at all once the turbo starts to spool by 2200.

When the weather gets a little more clement I'll attack the wheel wells.
 

Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
I am cross-posting this from the MKIV forum:

So my new Yokohama YK740 gtx 225/50 r17 tires are, using the same iphone app I’ve always used, a full 3db quieter than my Michelins. They’re expensive tires, all season, about $160 each, 60k life expectancy. I will post the exact name later.

I am now reading 67db at 70mph on good roads. Yes, re-read that: 67db. That's 10db less than when I started this process.

For reference, a 2018 GTI read roughly 70db across several different tests (different days, weather).
 

dremd

Veteran Member
Joined
May 31, 2007
Location
South Louisiana
TDI
06 sprinter. 03 jetta wagon premium with 6 speed ALH swap, 14 JSW
That’s impressive. That’s about what my Tesla is, but it has big noisy tires and leaky door seals.
 

NewTdi

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Joined
Jan 15, 2004
Location
NorCal
TDI
2003 Bora, Reflex Silver
I just installed some Nico product in the roof of the wagon and I forgot to do a pre and post installation reading. Doors are next along with anything else I can cover with the product such as the trunk, spare tire area and hood. I was wondering if it would be beneficial to perhaps spray some foam in the A, B and C pillars to cut down on the noise. I appreciate hearing about the wheel wells; I did not think about that. I After I get my noise level down I will be installing better front speakers and tweeters. As far as tires I am running Bridgestone Touranza Quiet Track and they are quiet. When on long trips I have them at 40psi to try to maximize mileage and get a little more vibration however at 32 they are noticeably quieter to my ears.
 
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Judson

Veteran Member
Joined
Jan 18, 2001
Location
Cheyenne, WY
TDI
2001 Jetta
For reference I am running the app dbmeter on an iphone 10. In the past I have run a different app on an iphone 6 with similar results on the vehicles I’ve tested.

I have not addressed any pillars or the headliner. I would like to hear from anyone who’s done so and achieved measurable improvements.
 
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