Door Sound Insulation Repair
 

Door Sound Insulation Repair

Just as my 993 was nearing the 60k mile mark, I noticed a clunk-clunk sound when lowering or raising the window. I thought maybe the window was coming out of the track or the motor was going out. Turns out, it was the sound damping strip that had come loose from the inside of the door and was fouling the window as it went up and down. This posting describes what I did to fix the problem.

In order to determine the cause of the problem, I had to remove the door panel, peel back the plastic seal and inspect the inside of the door. What I found was the damping strip had dried up and fallen away from the outer door skin. It looks like a piece of tar paper. Probably the oils in the tar-like product interacted with the adhesive and resulted in adhesion failure after 15 years of heat cycling.

I reached in and pulled out the damping strip and then tested the window operation. It worked perfectly, so I knew this was the problem.

I looked at my various options for repair and decided to replace the Porsche sound damping strip with an aftermarket product by Dynamic Control called Dynamat Xtreme. They describe Dynamat Xtreme as a patented, lightweight, elastomeric, butyl and aluminum constrained-layer vibrational damper. Dynamat is a peel and stick product. The aluminum layer is 4 mil thick. Weight is .45 lbs/square foot.

I also decided to replace the Porsche plastic door seal with another aftermarket product by Cascade Audio Engineering (CAE) called VB-2. They describe VB-2 as a lightweight, highly formable, vinyl based damping sheet that contains a silica mica and ceramic load incorporated to convert panel resonance (vibration) into low level heat through friction.

CAE also makes VB-5 which I used to replace the disintegrating foam used by Porsche around the door latch cable to prevent any possible rattles or panel buzz. VB-5 is a thin (1/8 inch), closed cell urethane foam with a peel and stick backing.

Here are the steps I used to repair the door sound insulation.

• Remove the door panel, speaker enclosure, window switches and door pocket/speaker cover.
• Peel off the plastic door seal.
• Remove the old damping strip.
• Clean the outer door skin surface of old adhesive and tar residue.
• Install the Dynamat damping sheet.
• Check the bolts on the inner door skin for tightness.
• Lubricate the window lift mechanism pivot points, wheels and gears.
• Remove the adhesive residue from the plastic seal on the inner door skin.
• Install VB-5 to prevent panel buzz or rattle by the door latch cable.
• Use the old plastic seal as a pattern to make a new door seal from VB-2.
• Install VB-2 onto the inner door skin.
• Use a heat gun to conform the VB-2 to the door skin surface indentations.
• Cut out holes for the 3 door handle bolts, the speaker, and the 3 snap connectors.
• Refit the door panel, speaker enclosure, door pocket/speaker cover and window switches.
• Check operation of window, door latch and speakers.

Photos from the project can be found here:

https://picasaweb.google.com/bruce.c...I3EnqvuzJGrSA#

A little about some of the chemical products used in this project. For cleaning the adhesive residues off the door skins, I used several chemicals. For the outer door skin, I used WD-40 and a toothbrush to remove the tar-like residue.
I then followed this with Zep Citrus Degreaser and a water rinse. Then to finish it off, I used Zep Foaming Glass Cleaner. This prepared the surface very well for the Dynamat installation.

To remove the adhesive residue from the inner door skin I found that acetone worked the best. I then followed that with the glass cleaner. Again, this prepared the surface for the best possible adhesion for the VB-2 damping sheet.

I used Wurth HHS-K to lubricate the window moving parts.

Reasoning Behind the Choices Made - OEM vs Aftermarket

My 993 is completely original, except for the new door soundproofing installed. My thinking is that this is not a museum piece nor is it a track car, and since the installation will be completely out of sight, why not use the best modern materials available?

I chose Dynamat to replace the Porsche damping strip for the outer door skin because I believe it to be a superior damping product. I don't think it will suffer from the problem of adhesion failure and it's ability to dampen structural resonance in doors is well proven.

The Porsche plastic door seal on the inner door skin serves 3 main purposes: 1) to act as a moisture barrier, 2) to act as a sound absorber, and 3) to provide a re-sealable means of access to the interior of the door for service procedures. I was, however, disinclined to refit the Porsche plastic door seal for a couple of reasons. As a moisture barrier there can be no argument that it does that job quiet well. However, as a sound absorber, it is not very effective relative to Dynamat or VB-2, both of which can function as moisture barriers and sound dampers.

I chose VB-2 over Dynamat to cover the inner door skin for a couple of reasons. First, the best damping performance will be achieved when the damping sheet has maximum contact with the vibrating surface. Dynamat would be difficult to conform to the various indentations of the inner door skin. I think it is really best used on flatter surfaces. Secondly, I was concerned with the ability to access the inner door for future service related needs. With VB-2, you can simply cut out the access holes when needed in the future and then patch over the hole with a piece of VB-2.

Note that although the VB-2 measures .045 inches thick and the Porsche plastic seal measures .007 inches thick, this extra thickness has no impact on the fit of the door panel.

Results

I am really very satisfied with the results of the installation. It has lowered the noise floor a lot. I don't have access to a sound meter to provide dB numbers but it is simply way quieter than before at idle and at speed. In one test Dynamic Control says a Nissan Sentra was 3 dB quieter at idle and 5 dB quieter at 70 mph.
But don't worry folks, you won't lose the Porsche sports car sound. That's still there and in my opinion sounds even better. The whole car seems more solid. This must come from the reduced resonance of the doors, and less road noise coming in through the doors. I drove around for a couple of weeks with the door panels off while I worked on this project and it is quiet interesting to hear how much noise comes in through the doors and the water drains in the bottoms of the door.

-bruce

Links to more information:

Dynamat Website:

http://www.dynamat.com/

Dynamat Technical Article

http://dynamat.com/download/2603_Sou...it_English.pdf

Dynamat Online Store:

http://www.dynamatstore.com/

Cascade Audio Engineering Website:

http://www.cascadeaudio.com/index.htm

CAE Online Store:

http://zeronoise.com/

CAE Soundproofing Blog

http://cascadeaudio.com/blog/index.htm



Porsche Parts Reference:

Porsche damping strip (PN 993-556-521-00). Cost about $10.31 from Sunset Porsche.
Porsche door seal (PN 911-531-889-00). Cost about $36.13 from Sunset Porsche.

Thanks for the write-up!


~ The Eagle ~
---------------------
'96 Polar Silver/Black C4S, manual, litronics, LED's in the positioning lights, alu/leather shifter & handbrake,
silver face gauges with alu rings, sport seats, full leather interior, motor sound airbox, stainless door sills,
valve caps Porsche crested brushed alloy, front protection bar, with split rear grill and layered with Meguiar's NXT Tech Wax :D
__________________
'92 Carrera 2 (Sold)
'89 Carrera 3.2 (Sold)

Excellent write up. How's the speakers sound? I installed the "foam surround cups" in my speakers cavity when upgrading my stereo and had to remove them. The sound was very tinny.

great

The speakers do sound better because there is less noise to overcome. But let's face it, there is only so to be gained when you only treat the door panels. I'm sure the rest of the car sound proofing is minimal and the audio electronics could be improved as well.

When you mention "foam surround cups" are you referring to the Deflex PowerPads made by CAE? Or are you referring to the foam cup that is part of the plastic seal? If your upgrade included replacing the HiFi speaker enclosure and you mounted your speaker directly to the door panel, then you might want to check out those Deflex pads.

Thanks for the write-up... I found that dried up old tar-paper inside my driver's door a while back when I was fixing the check-strap. Was wondering about replacement options and you saved me the research. :thumbup:

Very nice. Very, very nice! Thanks for the project details and product easy links.

Hi

Excellent

I am going to do the same now I have a roadmap!

Many tks

Berni

Bruce,

Not only did you document your DIY in exquisite detail and illustrate it with excellent photos, you provided the rationale for approach as well as links to the products. You have made it very easy for others to replicate your approach and to have confidence in the outcome.

I really appreciate the time and effort you have put into this and will definitely make a record of it for future reference.

It is contributors like you that make Rennlist such a great site.

I might take a peek behind the door panels myself - Thanks Bruce - and perhaps see you on the roads!

+993

Great write up. Thanks.

Thanks for the write up. I must have missed it the first time around. I will have to add this to my upgrade list.

Thanks,
Emerald

great thread...in my bookmarks since it started and I keep coming back and re-read.
this is going to cost me a fortune shipped from the US.
Cascade ships only UPS or fedex.
How much VB2 do we need to cover both inner door panels ? does the small kit 14 sq ft suffice ?
thanks

Hi, Thanks for the comments. The 14 sq ft will be enough to do both doors
easily. Let us know how it sounds when you're done. I'm really enjoying how
my car sounds now.

-bruce