Sound Deadening - Is 3M 08840 Alone Enough?

[tc911e]

My ‘69 911e project recently returned from paint and the reassembly process has begun. I’ve done a lot of searching and reading on different materials for reinstalling some sound deadening, but there are lots of different and often contradictory views on the right way to go about it. My core question is-

For those of you who have used the 3M 08840 sound deadening pad by itself- has that provided adequate sound deadening without adding additional layers of closed cell foam and mass loaded vinyl as some folks recommend?

I have one box of the 3M stuff and was planning on using either as a base vibration damping layer (which apparently would only 25% or so coverage of the flat panels) or as the only layer (which I presume would require a more continuous coverage that I’ve seen in a handful of posts). Just need to pick a direction before I get started. All of the interior has been stripped of the original tar covering since much of it had rust underneath and it’s been epoxy primed and painted.

[Nickelplated5s]

You will get better answers but go to a shop for semi's just to look. My hydraulic shop has multiple options. To my eye they are a lot thicker, 3/4"?

[62S-R-S]

If the floors are restored and painted, wondering if you need to have 3M sound materials adhered to the floor, which then loses the painted surface. You could drive it first, w/ carpet installed to test. Rubber companies will sell 1/16" thick rubber material, that once cut and placed under the carpet will help insulate. For extended trips, a decent pair of ear plugs is the best thing for quiet.

I once removed an engine sound pad and found no difference in the decibel level.

[xpensivewino]

I used 08840 on the entire floor of my 69 E and was very happy with the product. It adheres nicely and is easy to work with. I also used a small strip of it on the inner door skins. I am running a high quality jute backed wool carpet set, and the sound deadening is just fine.

[Jones]

Hey tc911e,
I'm at the same stage as you, nice fresh bare painted shell... I've also been researching sound deadening materials and have found some very good technical information (and products) from Resonix. Here is a link to a technical article that you might find helpful: https://resonixsoundsolutions.com/re...rmation-guide/

I have not purchased any materials yet, as I am still go through what's left of the materials removed from my car. Fortunately all of the fitted foam pieces from the rear seat buckets and parcel shelf area are all still good. The material I scraped from my floor (inside) was probably 3-4mm thick, so there is space there for sound deadener material under the carpet padding.

I'm curious what others have done for the roof of a non-sunroof coupe, (under the headliner), original seams to have been burlap and foam.

[NorthernThrux]

I used the 3M, installed in exactly the same places as the factory did. https://www.early911sregistry.org/fo...=1#post1027770

Then I got a perfect repro carpet set also detailed in that thread, and Coco mats in the front. No issues with noise at all. The motor dominates what you hear, even with a sound pad installed in the usual place in the engine bay.

Ravi

[SFE]

Here's what I used on my 69E.

[TheTorch]

This is a good primer on car soundproofing: https://www.secondskinaudio.com/soun...soundproofing/

Understand the differences between sound dampening, sound blocking and sound absorbing is key. In general, the common sound deadening (like dynomat) needs only cover larger flat panels that can vibrate (like the floor), and 25%-50% coverage is as effective as 100%, without adding unnecessary weight. They do not block or absorb noise, though you get some thermal insulation.

I don't believe our cars have panels that vibrate very much because of all the panel detents and unibody structure. For the floors, you can lay down a MLV + closed cell foam with minimal glue so you can remove them later if you want. The deadener -- well that's a mess to remove.

Luxury Liner Pro is amazing, but expensive, hard to work on curves, and shockingly heavy (1.25lbs per sf).



Having done the 3 layer approach on my car (with a net gain of maybe 25+ pounds vs. the tar and sisal crap that was there) , I would say it's remarkably quiet with the windows up, but in truth if you drive with the windows open, all you hear is wind noise, intake and exhaust. Would I do it again? Not sure about that.

2 cents.