Installing some new carpet: Dynamat over top OEM sound deadening?
 

Hey Gents,

Got my german square-weave carpet from Auto Bahn interiors and now that I have the carpet out, I am evaluating the stock sound deadening.Its in okay condition despite a few cracks and it generally being matted down.

My question is this: Has anyone applied a layer of dynamat over top of the OEM sound deadening, and then the carpet to the dynamat? How would adhesion be with dynamat on top of the OEM stuff? Would it be better to just pull the stock SD and put down fresh Dynamat (maybe multiple layers if needed)?

I did search, just didn't see anything relating to this specific subject.

Sorry if these are stupid questions...

Yes

I concur^^.

But first, a few cautions. The OG sound deadening material's biggest drawback is its ability to hold water which, eventually, will begin to rust the floor while being unseen. If you simply cover the old with Dynamat, if any rust has begun, you will never know until it's too late. Cleaning off the old material, inspecting the metal underneath, and addressing any rust issues found, is the first step.

As far as how much Dynamat to use, that is another topic for clarification. You do not need to cover the entire metal floor, nor do you need two layers. Dynamat is a sound dampener, which means, it is designed to reduce the vibration frequency of the sheet metal, not block sound waves. Dynamat is dense and heavy, and just like the OG material, it's function is to eliminate/dampen sound frequency of the metal, not eliminate outside noise. The little pieces inside the door skins is what gives the Porsche "ping" sound when the door is closed. The door is not totally covered. Two layers of Dynamat will add significant weight without significant sound reduction.

If you want to make the interior quieter, much better sound reduction will be gained by the carpet or even a layer of automotive carpet padding laid between the Dynamat and carpet. If you choose that route, do not glue the padding down and be ready to remove the carpet and padding should you get any water into the interior.

Thanks guys. Didn't consider the rust issue. That might make my decision right there.

I'm planning on being certain that my windows and doors don't leak before I put an interior back in. Test for leaks before you recover the floor.

Rust may be your biggest concern. And, you won't notice this rust until it's too late.

I just used the OEM/Wurth and it works fine.

http://forums.pelicanparts.com/uploa...1483476416.jpg

Richard Newton
Historic Racing Images

Well crap. I pulled back the sound deadening and, sure enough, the entire bottom of the driver-side bucket is rusted through.

This is what I get for trying to tackle a "small carpet job" on my own.

Thank you LJ and Richard for pointing that out. I might have covered new carpet right over a looming rust problem that would have only gotten worse.

...I need a beer

I removed the existing material and fortunately had 0 rust.
I applied the Wurth OE sound dampener that i believe Porsche / VW use.

Really happy with the results.

Alex, I removed my original sound deadening last year - not the funnest 911 job but not the worst either. Lots of info on how different guys did it. I primarily chipped it off with a flat blade screw driver and wooden mallet. Took some time and safety glasses are recommended. Months later I was still finding small pieces in different corners and such.

I agree with ossiblue about how much Dynamat to use. Not too much and not two layers.

Good luck.

I used one of these from HF Oscillating Tools - Oscillating Multifunction Power Tools and removed the old sound deadening material in no time! ;)

Dry ice and a rubber mallet.

Only using dynamat will not work. If you're after real sound deadening do a search for user Nineball and read his threads on the subject. Basically he says you need three layers. The downside is that good soundproofing is heavy, over a pound per square foot.

I've been looking into the offerings of aircraft spruce. They have a system that's a half pound per square foot. Seems like a decent compromise. I don't need a luxury quiet car but it is nice to be able to hear what a passenger is saying.

Alex & all, you guys are on it! I agree with everyone, here is one other option. After removal of old carpet & padding, the clean & prep for new material is the hard part. Like most-I used Dynamat as base coat, then a friend showed me a new product called; B-quiet. Basically it's a rubber lining with a thin cushion of foam applied on top of the Dynamat. Then the carpet on top to complete the process.
My car (87) is a cab, so noise is always present, however with new interior, it's much better. Good luck with your project.
Terry

Sounds like the OP is now facing a floor repair. Welcome to the world of the slippery slope. Really not a big deal, but something you weren't expecting. Look at it as a fortunate discovery. If you want to return the car to original sound dampening, Dynamat or any other deadening material will work, and the amount need not exceed the amount of the OG material. Butyl based is better than asphalt, IMO.

If you want to increase quietness and road noise, you need to look at other materials which have air gaps, like open cell foam. That, however, introduces the possibility of water retention once again. Sound deadening and sound absorption are two different things. Porsche did not use sound absorbing materials on the floors, outside of the carpet. On the doors, the plastic water barrier and panel cards served the purpose of stifling outside noise from entering the cabin--however poorly. Covering the holes in the inside door frame with the plastic barrier cuts down on the acoustic waves entering the cabin.

Pretty much this ^^^. Everything sound deadening is on a temporary hold until I address the rust issue. Taking the car to a body guy when I return home from San Diego to get an idea on the scope of this new project now upon us.

I did see nineballs post on the three step process, and as much as I like it, the weight is too large a sacrifice for me. Returning to at least a stock level of sound deadening is my goal here. Any less and the Mrs. won't let me take it on long trips.

I will have to look into BQuiet as well. It sound similar to the DynaPad made by dynamat that I was considering for the floor panels.

I'll post some pics of the rust when I get a chance...:(

If the rust is in the usual place, rear passenger seat bowl, it's a fairly simple patch job....accessible from top and bottom, and depending on the size, weld a piece of metal or buy a pre-cut piece from salvage or a re-pop.

What I'm trying to wrap my head around is how to get the carpet to lay smooth with all the recommended layers of dampener and deadner. It seems like there would be a lot of cushioning and therefore difficult to get a clean look.

Good link

And to the original poster, think of dynamat as a replacement for stock, not a supplement.

The original factory supplements in different parts of the cabin were horse hair and carpet backing ( as well as back seats...they are the biggest sound proofing component in the car)

Today there are more modern materials than horse hair

I used aircraft spruce closed cell foam over dynamat and that helped, but mass loaded vinyl ( or back seats) are a necessary next step for me to drive without ear protection

^^^^ This.

I removed my rear seat backs last weekend (left in the bottoms for now) and was really surprised at how much more mechanical noise came into the cabin. Other than the volume increasing and other sounds becoming clearer, I can even hear the clutch engage now whereas I couldn't before.

I noticed this as well. Ill be interested to see how loud it is with carpet, seats and sound deadening out, when I take it to the body shop next week.

Thanks Mickey. And your right, in the grand scheme of rust, this could be alot worse.

With regard to the carpet laying smooth, I'm wondering if the extra padding might make it easier and more forgiving for some of those awkward corners and curves (This is probably just wishful thinking)

I've always wondered what that will do to the undercoat. Does that stay on?

There was a video of someone using dry ice on the floor coating...pretty impressive how it made quick work of it. I don't recall them making any mention of the undercoating.
My area dry ice isn't something you can just pick up anywhere so I used the HF electric cutting tool and that worked well.

A heat gun and any scraper will make quick work of the sound deadening. The tough bit is the carpet glue. It's pretty awful. Plenty of threads on it (most involving CitrisStrip), all involving labor.

^^^ Agreed. A heat gun to warm the deadener just enough to make it pliable like taffy. Don't melt it. Once an edge of the deadener is lifted heat between the deadener and the floor pan it will come out in sheets.

I've been observing the noise levels in the P-car 89 3.2 coupe and 06 Tahoe (both are parts getters for the other). What I'm hearing is very large changes in noise levels depending on the road surface at highway speeds. E.g. say there is a newly paved section (quiet relatively smooth) and the new paving section stops and I hit the "old" rough section, the noise level increases dramatically. This tells me that the noise at highway speed is largely coming from the tires not the engine/trans. So the question is - where/what is used to most efficiently reduce the tire/road generated noise?

New tires.

Hello
I did not know how Dynamat worked when I did my first car and I ended up lining every inch of the interior with the stuff. It did reduce vibration noise and most of the chassis drone, but it was unable to reduce most of the outside sound, and it did add considerable weight. After reading to many posts regarding sound absorption, I decided to do a three layer approach in my second car using Dynamat, Dinaliner and Dynapad. I started with Dynamat only in the recessed portions of the sheet metal, then Dynaliner on the roof, doors, and on top of the Dynamat. To this I added two pieces of Dynapad on the floors under the rug. This definitely brought down the noise to almost contemporary car level. It's still very heavy but not as much as the complete Dynamat solution. Dynaliner is a very light two layer foam material. Dynapad its a very heavy three layer foam material of three different densities.
Hope this helps.
Cheers
MD

@hcoles The wheel wells and the floors.

Read the following post. Dynamat is not meant to reduce outside road noise, only to dampen the noise from sheet metal vibrations. Road noise reduction requires a sound absorbing material like open-cell foam. Your carpet, alone, does a minimal job but does help. Adding absorbing materials under the carpet and behind the side panels (attached to the back of the panels, not the metal skin of the car, and between the vapor barrier and door card) will reduce road/outside noise considerably.

Good point - the noise generated by the tires on the road can go "outside" and try to get in via the doors/windows/etc. I don't know how much that (outside noise long path) is compared to the noise coming off the tires and coming in directly (short path) via noise vibration of the wheel wells/floor pan/etc. I was referring to the noise coming in via the wheel wells/etc. Good points re. damping noise coming in via the outside long path.

Thanks.

While we address the rust issue, I have been researching, going back and forth of what level of sound deadening I want to take this, while still keeping the weight in check.

Once I've prepped the surface from the old sound deadening and have the new pan primed and paint my plan is to follow nineballs method of a 40-50% coverage of a butyl based Dynamat. But then I am torn as to whether to follow it with some mass-load-vinyl or closed cell foam, to reduce the engine and road noise, before laying carpet.

But side note: Here's a photo I snapped yesterday while checking up on the progress. Rusty pan out, new pan on its way in!

http://i391.photobucket.com/albums/o...39%2023_1.jpeg

In my '84 I laid down on the floors 1/4" closed cell foam (CCF) backed with 1/8" mass loaded vinyl (MLV). I did not scrape up the old factory sound deadening, I then put the regular carpet back over the top. It made a noticable reduction in road noise.

The engine and trans do make a lot of noise (not just exhaust noise) that make it's way into the cabin. I noticed new engine mounts made a reduction in noise as well (standard, Genuine Porsche mounts because the standard aftermarket ones failed after a couple of years).