sound deadening - floor area

[randywebb]

Hi Jay - I am posting your Email here so everyone can benefit. First, I am not a acoustics expert per se. I'm a scientist who has worked with acoustics in studying birds, their physiology and how they do what they do. That gives me a fundamental knowledge of how sound works. I also have an interest in hifi (audiophile) stereo sound systems.

It seems that your question is how to sound deaden the floor area on your car. First, I would have used a rust reducer _before_ putting on POR-15. I hope no rust is trapped below the POR layer. You want to consider what noises are coming thry the floor - they will mainly be from inpact on the underside, I would think. So i would make sure I had a good coat of undercoating on the other side. I'd make sure that the floor panel vibrations were damped by putting strips of sound deadener there. I would not use lead strips as the PO of my first 911 did - toxic and too heavy. CAE, Cascade Audio Exxx (the E is for something but I don't remember what. see odl thread on that) is one brand that seems good. To save wt. you can put this material down in strips rahter than whole sheets. In my doors I crossed the strips. This type of material reduces panel resonance. Then you can spray a mciro-bead type spray. That will absorb the sound and turn it into miniscule amoutns of heat. Then add a pad material fibers or foam over that. Last, the floor mats on top will also help reduce sound transmission. This can all be done with equal or less wt. than PAG did in the 90's and 70's. And I expect there will be less sound transmission than stock.

Understand that the desire to have a luxury car is often directly at odds with the desire to have sports car....

There are lots of threads on the rust reducer/POR-15 issue and on sound deadening. You'll find them with the search button, the right terms & a fairly large amount of winnowing.
Post any followup queries here, and if you find some good threads you could link them here for other people to use.

Good luck - Randy
______________________________

Hi, Everyone seems to say your the resident expert on sound deadening so I have a question or two for you.

I have taken the sound deadening (factory stuff) out of my car to inspect the floors for rust. I found surface rust some fairly aggressive but no holes. At any rate I have cleaned it up and used POR 15 to treat the floor.

I don't like the vibrations that transmit up into the drivers companion now. I am about to order a bunch of dynamat but am not sure what is the best for my
application.

Right now I am mostly concerned with the floors. I only took a small portion of the back seat actory sound barrier stuff out to inspect for rust...all looked good there. I will either patch what I took out or pull it all out and replace
with something else ...haven't decided yet.

Do you have any suggestions or thoughts.

Jay Zittrer

[clevy70911T]

Originally posted by randywebb

It seems that your question is how to sound deaden the floor area on your car. First, I would have used a rust reducer _before_ putting on POR-15. I hope no rust is trapped below the POR layer.

I thought POR15 was Paint Over Rust? Somewhere on my can of por15, it recommended using the prep spray, then the POR15 right on top. Removing all the rust down to metal was not recommended if my memory serves right. At any rate, I don't think anyone should fret over having used POR-15 on top of rust, as long as there wasn't any holes or loose rusty metal. I love the POR-15 and have used it for over 12 years.

Just my 2 cents.

[Allenk]

Por-15 is an encapsulating paint for rusted metal.

[jmz]

Thanks Randy.
I appreciate your thoughts on this. I will incorporate this into making my car a more enjoyable sports car to drive. I still have the factory stuff behind the back seats and haven't decided if I will fully remove it. The test areas I removed showed shiny solid metal underneath so rust is not an issue there. I likely would benefit both on weight and better sound absorbtion by removing and replacing the factory sound deadener but man that stuff is hard to remove!

as for the por-15 product, the instructions say it works best to put it on to seasoned or rusty metal. I cleaned it up with a wire wheel before applying the Por-15. I used there metal ready primer before applying there sealing painte. I think I will be in pretty good shape. The rust was only bad in a few small areas ...I like to think of it as a method of lightening my car. I now have thinner sheet metal w/o the expense of owning a 911R- RS or RSR!

[Zeke]

I don't know if this thread is going to be more baout POR-15 or sound, but I'll offer my POR-15 knowledge.

POR-15 appears to be a single componet urethane with a high gloss and no UV protection additives. It is never a good idea to paint a gloss material over a smooth surface.

My belief is that the best case senario for the application of POR-15 is to remove as much rust as you can mechanically and then treat rust in pores and seams with the metal prep (phosphoric acid). Before painting on the POR-15, it is a good idea to degrease the metal and scuff with an agressive 3M pad or med/fine sandpaper. Vacuum or blow, then paint. You should cover up POR-15 with mat, carpet, undercoater or paint in exposed areas.

HTH with the treatment before installing your sound deadening material.

[randywebb]

I think you'll be ok with the way you did the POR-15. IF it rusts thru after you die of old age, do you still care?

Zeke's method is the optimum, I think. But I like using a rust reducer also - it chemically changes the rust (reduction is the opposite chemical reaction to oxidation -- rust is oxidized iron).

Back to sound:

I discovered that Aircraft Spruce has several types of sound pads in their catalog, and a free booklet on them. I haven't reviewed the booklet (yet).

Yes, it is hard work to remove the stuff behind the seats. To paraphrase:

"Light wt. takes sweat. How light do you want to go?"

[autoxracer31]

Quick question about removing the factory sound deadening:

What tools are required and how hard is it to remove all the material behind the carpet and rear deck areas? I want to redo all the deadening but also use the same carpet again...thanks

[rdane]

FWIW on my '79 I stripped the interior clean in 8 hrs with no mechnical skills to speak of.

That includes taking a drill with a wire brush on it to the bit of rust I had and repainting with POR-15.

I then added several products from
http://www.b-quiet.com/dynamatinstallation.html

That total install was another full day. Took a bit more matt to stop the heat exchange into the cabin but not a big deal just needed more coverage than originally planned.

My car ended up a bit lighter than factory and much more quiet.
I am happy with the end result and more importantly so is my wife.

Getting carpet back in was a bigger hassle than the sound matt coming out and going back in.

[RoninLB]

Originally posted by autoxracer31
What tools are required and how hard is it to remove all the material behind the carpet and rear deck areas?

I used a heat gun to loosen the glue for the scraper. Then tolune. Then paint store alcohol.

[randywebb]

Yow, Ron! Those are some dangerous chemicals. Even with a real respirator, you will have a lot of skin absorbtion. I would not use toluene at all. At a minimum it will make your posts hard to read....

There are some posts on what people have done - the search button will find them. I forget, but I think heating was better than ultra-cold (dry ice).

[autoxracer31]

Once you got all the new sound deadening in did you glue on the carpet or how do you put carpet back in?

[rdane]

I used some sort of 3M automotive trim (carpet) glue.