I purchased a couple rolls of Farman adhesive backed sound material with the aluminum foil top. Curious what everybody’s thoughts are for using this in the interior, on the floors and behind the back panel.

Thinking simply roll/press it down with a roller and then tape the seams. Are there other ways or material that people prefer to use as I keep thinking of the moisture that at some point will likely get under the sound insulation material even if I tape it.

FYI, I did replace the floors then coated entire floor top and bottom with Por15, followed up with paint so I’m starting with a very nice surface. I know I can put this down and will be fine for probably at least 15 or 20 years but I would like to think I could make it last longer so the next guy won’t have to worry about rust. Like to know what others have done and what their experiences are.Click to view attachment Click to view attachment

There have been some very detailed discussions and great technical information courtesy of some of the members here that are actually in the car manufacturing business. As ever it depends what you’re going for, but the single biggest tip I could offer is don’t feel like you have to cover every inch of the panel to achieve a significant reduction in NVH.

Some adhesive that gets pressed onto the floorboards will go along way, it’s the rear firewall that arguably needs the most attention.

Keep in mind that a lot of Road in engine noise will make its way into the cockpit no matter how well insulated the firewall is due to the design of the car.

^ Yep to all that.

Not such a big deal in a 914-4 (especially with FI), but a six conversion with carbs has had me thinking about a bit of sound deadening under the front part of the engine lid and maybe even a doubled rear window with a gap between the panes. Top off, the six is lovely. Top on, not so much on longer drives.

With all of the seals sorted and factory sound deadening, 914-4s can be wonderful long-distance cars—fast, efficient, and surprisingly quiet for what they are.

Has anyone installed the sticky stuff cut to fit in the low-spots of the floorpan? Wondering if that’s do enough and ‘flatten out’ the floor at the same time.

I also might put a square in each door to help the tin-can sound resonance. But I’m just spitballing at this point.

As you can see, I placed the sound/insultation material on the firewall and longs throughout the cabin. Essentially I put the barrier everywhere except over the tar mats. This included the footwell area as much as possible. Installation was easy using a roller. The car is still on my lift so I can't speak to the effectiveness of the material but I expect a significant improvement in noise level. I also replaced the outside firewall material in the engine bay. Since I am converting to dual carbs I wanted to make sure I keep the cabin semi-quiet...... Good luck!

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I tried this... Now its not quieter, is duller. Nest time I plan on using spray on acoustic stuff.... Any NASA guys here have access to any? I like using modern tech in our old cars.

Matt

^ This is a very interesting input.

Can you elaborate a bit more, both on what you did and your observations? Going to redo my floors at some point, and have been watching these threads with keen interest.

Fwiw, a visit to the restoration shop that handles restoration work for Porsche Classic revealed 997 (?) sound deadening mats instead of the old-school stuff. Kind of a gray, diamond-shaped pattern iirc. I suspect the choice was driven by a matter of cost, weight, effectiveness, and/or environmental impact/legislation. But I'd like to learn more, and suspect that whatever Porsche and other manufacturers is about as good as it gets in terms of those four parameters.

On a related note, and because this was brought up, I am a huge believer in liberally adding sound deadening to the doors. It makes the experience of hearing the door shut sound approximately $84,172 more expensive (+/- $40,000).

The only car that I didn’t do this to was my 1972 350 SL which came from the factory with bank vault doors.

Do it - you won’t regret it.

I used Eastwood X-mat all though the cabin. But didn't do the doors, (I ran out at the time) Next time I have a reason to open them up I would like to add sound deadening to them.

I have also toyed with the idea of adding some X-mat to the engine tins. Not where the cooling air goes, but to the bottom around the perimeter.

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After changing the floor pans. After owning the car 12+ years. After owning several old Mercedes-Benz. I decided I wanted my car quieter. Most people are worried about adding the extra weight, not so much right now. Engines can always get bigger. I installed the Eastwood version of Dynamats. It was done on all the floors and the back pad as well. Nothing has been added on the inside of the engine compartment yet, I wanted to spray a ceramic insulation on it. I figured Dynamats would just peel off due to heat. The doors were sprayed with undercoat on the panels inside where the bracing is. Then one sheet was slid over the door opening as the factory did with the plastic. Like I said it did not make it quieter it made everything duller. Made the doors sound more expensive and heavier. Would I do it again, yes. I would use the most advanced material that can be had. I just don’t know anyone that works for a major car company that would have access.
Matt

Been thinking about this while rebuilding my doors.

One concern has given me pause: Moisture buildup between the sound pad adhesive and the door skins—especially as the doors get wet or humid. Been trying to decide if that's a legit concern or not? Or…could the deadening be added to the door card side somehow?

My 72 already had sound/heat insulation on the back. I put it inside my doors and they sound a lot more solid when I close them. They don't sound like a tuna can now. it's got to help with road noise. I was a little reluctant to put it on the floor thinking it may trap moisture and promote rust.

Has anyone tried lizard skin?

Make sure you reseal the rear window. Water, as well as noise, gets into the cabin from a loose rear glass. Replace the rubber butyl seal if you haven’t done so.

I put an adhesive sound deaden
Material called Noico on both sides of the firewall, as well as the floors and inside the doors. It makes it quieter, but it will never be as quiet as a more modern car. You also have to replace all the rubber seals on any cables or wiring that goes through the firewall. Sound will travel through the smallest holes.

Not yet, but was planning on using it after primer, but before paint on my next interior.

Same process I used on my last build when I added the Raptor Liner to the entire undercarriage.

I don't think it is an issue, you don't need to do the whole door and it is a vertical surface.

I've wondered about this stuff—which is supposedly noise and heat insulation.

https://www.restomodair.com/shopproducts/me...rmal-insulator/

IMHO I'm not impressed with any of the aftermarket stuff I've used. To me it's too thin worthless crap.

My /6 conversion I re-used the stock firewall pads inside and out. I did modify the pad and added more fasteners, etc.

Not worried about rust, not a speck under the pad and I don't leave my car out in the rain.

Keep in mind that different sound deadening materials are needed to dampen or insulate different types of sound. There is a reason the factory installed tar sheets on the floor and a thick tar-covered fiber mat on the firewall. The foil faced, butyl based mats most commonly used are intended to dampen vibrations. There's a great demo of how that works 30 seconds into this video: https://www.youtube.com/watch?v=P4ylKyoY_oU Those mats work great on floors and inside door skins to eliminate drumming and resonance. As was mentioned, put a couple strips of that inside your doors and you will get that solid German "thunk" when you shut the door instead of the cheap tinny ring of untreated doors. Those mats aren't going to help as much on the firewall although they'll help.

For deadening exhaust and engine noise, you want more of an insulating material. Open cell foam and fiber mats are often used. That's really what you want on the firewall in addition to a vibration dampener. Don't overlook the importance of tight weatherstrip for sound either. Sealing the rear window was already mentioned, but sealing around side windows helps too.

As far as moisture trapping. I think it is a non-issue with the modern butyl based mats. When those are rolled on properly, you are really adding a thick layer of mastic tightly bonded to the surface which should increase moisture protection rather than trap it. It's very different from the original tar.

The firewall mat works because it's a heavy rubber mat with the open cell insulation backer, the metal, then cabin side rubber mat and the backpad. It's the layers that do the job, you eliminate one or more layers the louder it gets.

The clean bare firewall may look cool, but I hope you like wearing ear plugs.