Floor tar repair/ restoration Options

[TonyA]

What does everyone use to repair floor tar sound deadening material. I have some popping up very little rust the cause of course. I am removing a small amount to good sound completely rust free areas and want to restore that to like new appearance. Any suggestions?

[914_teener]

Just curious....those interiors look beautiful.

Why not dampen the firewall (inside behind the backpad) the the foreward wheel wells and front bulkhead? Those are two next largest resonant metal panels.

With regard to "sound absorbtion" and "resonance", two different things.

I've worked on a couple of projects in my career where both were concerns.

Sound absorbtion uses different ways to "disrupt" the sound waves.

Sound resonance damping is what you guys are talking about. It's the actual transfer of the sound energy to the metal panels. Like a shock absorber on a car.

Sound absorbtion is a sort of vodoo science...really cool stuff almost like quantum physics applied.

Curious about the comaprison since the only differnece I see from the layered product is the layered composition and buytl....other than that....it's the same stuff in layers of foil with sticky Avery crap on the backside.

[bbrock]

Why not dampen the firewall (inside behind the backpad)

I actually did that. I still use the stock rubber sheet on the interior of the firewall but added a layer of foil faced (constrained layer) butyl on the engine side that is hidden beneath a sound absorption mat made of modern materials.

Curious about the comaprison since the only differnece I see from the layered product is the layered composition and buytl....other than that....it's the same stuff in layers of foil with sticky Avery crap on the backside.

I don't know how accurate this is, but what I've read about the modern foil-faced butyl stuff is that the butyl adds mass to reduce the vibration of a panel and also absorbs the energy of sound waves moving through it. As waves propagate from the panel through the butyl, the foil reflects some of the waves back through the butyl to further dampen the energy so less "escapes"through the mat to travel to our ears. Seemed reasonable to me when I read it anyway.

I've also seen rules of thumb about the percentage of a panel's surface that should be treated to achieve sound dampening. I'm not sure of the physics involved but seems there are diminishing returns beyond a certain level of treatment. The stuff is kind of spendy so optimizing for biggest bang for the buck makes sense.

Of course, the shape and size of a panel has a huge difference in how much they vibrate and resonate sounds. Like @Superhawk996 said, it gets really complicated and is way beyond my comprehension. Treating the large flat surfaces makes the most difference. Of course, if money is no object and you aren't worried about weight, I suppose covering all the panels with sound dampener might make the quietest car and some people do just that.

Another area that makes a huge difference is inside the door skins. I don't remember if early doors had tar added but the heavy late doors did. A strip or two of sound mat inside the doors makes an enormous difference. I cringe every time I watch a video of someone shutting a 914 door and hearing that tinny ring that makes the car seem much more cheaply built than they were.