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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 07-11-2014, 12:16 AM   #1
Registered User
Join Date: Jul 2014
Location: Finland
Posts: 5
My Ride: 318i Touring
DIY: Reduce road noise! under 50$

Here in Finland we have many old or rough roads and therefor i wanted to do a attempt to reduce the noise in my e46.

I went through alot of pages to find out which insulation material would be best to use. There are many to choose from, but most damping mats like dynamat are pretty expensive.

Found a thesis about this, where a 10mm cheap-copy of dynamat (vaim1) was compared with 1.2mm bitumen (vaim2) and 12mm foam (vaim3).
Here is a table of how goodly the mats can reduce noise:

Whole thesis can be found here (Finnish): Click

As seen in table the bitumen mat reduces noise by a avg. 33%. And they are also pretty cheap, 8$ for 500mm X 1000mm sheet.

What do you need:
- 8mm rachet wrench.
- 17mm rim wrench
- Jack
- Phillips screwdriver
- Screwdriver
- Brush
- Alcohol for cleaning
- Scissors
- 3 kg of Tectyl bodysafe or similar (Picture)
- 3 kg of bitumen rust mass or similar (Picture)
- 4 sheets of bitumen mat ( 4x 1,2x500x1000mm)

If possible, wash and clean your inner fender wells a few days before you do this! Need to be completely dry when doing this diy!

- Start with taking off your rims

- Undo all 8mm bolts/(nut) that keeps inner fender in place.

- Clean the area that have been under the inner fender with alcohol or similar to get rid of dirt and fat.

- Cut pieces that cover at least 1/3 of the metal area.

- Place mats around and cover much as you can. (don't cover screw holes)

- Apply Tectyl bodysafe, this will work also as a glue that holds the bitumen mats there. Apply thick as possible (~1,5 kg / front fender).

Let it dry for at least 60min.

- Install inner fender
- Clean inner fender and surroundings with alcohol.

- Apply Bitumen rust mass thick as possible, as a second layer of noise reducer ( ~1,5 kg/ fender).

- Install rim, let dry for at least 60min.

- Test drive.

I have also applied Bitumen rust mass in rear inner fender wells, and installed bitumen mat in trunk where possible and around the spare wheel holder.
And will also apply under the car when i have some spare time.

You probably wonder now how much this reduces the noise.

I done 3 testruns ( 3x 10km ) without any modifications. I used "Noise meter" android application, it might not be 100% accurate, but it'll show the difference between measurements.
318i Touring -00, Continental ContiPremiumContact2 205/55R16, AC off, stereo off.
~90 km/h ( ~56 mph )
1. avg. 72,2 dB
2. avg. 72,8 dB
3. avg. 71,9 dB

And after:
1. avg. 67.3 dB
2. avg. 66.9 dB
3. avg. 67.5 dB

-> Avg. reduced noise = -5 db !

Did also a short test at 120 km/h (74,5 mph) that showed 76 dB -> 69 dB (after).

Last edited by MaskN; 07-11-2014 at 12:21 AM.
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Old 07-11-2014, 10:43 AM   #2
Registered User
Join Date: Feb 2010
Location: Houston, Tx
Posts: 61
My Ride: e46 soon.
Nice, not to familiar with the db noise rating. is a 5db a noticeable difference?
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Old 07-11-2014, 11:29 AM   #3
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Join Date: Jul 2014
Location: Finland
Posts: 5
My Ride: 318i Touring
Originally Posted by Acrono View Post
Nice, not to familiar with the db noise rating. is a 5db a noticeable difference?
Originally Posted by gcaudio.com
Official Perceptions of Increases in Decibel Level
Imperceptible Change 1dB
Barely Perceptible Change 3dB
Clearly Noticeable Change 5dB
About Twice as Loud 10dB
About Four Times as Loud 20dB
As reference; normal conversation between 2 persons ~65dB, vacuum cleaner ~75dB
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Old 07-11-2014, 02:48 PM   #4
K-Space Hero
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Join Date: Jul 2014
Posts: 6
Very nice! I've had a similar idea...And now I have a great reference. Cheers!

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