Ya stupid as* questions, OK I am pondering welding up the top on my V8 car because I like the idea of having a closed cockpit. What I don't like is the noise level and have found I can install another rear glass with about 1/4 inch gap between each peace of glass. I think I have ample room for insulation but surely someone has gone in this direction before. Can you quiet down the cab via insulation technique's ?

Will your interior pieces still fit? Good idea for sound.

A previous thread on the subject that I bookmarked:

http://www.914world.com/bbs2/index.php?act...mp;#entry574725

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The vinyl pads will have to be trimmed but you wont see any difference, I don't have a targa pad yet so Thats not a big deal to me. You just trim the inside a bit no big deal to me. My friend in Washington state who painted my can can make a top in his sleep, and has a friend who is real good at shaping steel a real old time craft lost to most. I know the steel top wont stiffen up the car much, may help a bit and can't hurt.

I did coat the hole inside of the cab with dynamat, I didn't do the doors but have a thick insulation pad on the fire-wall. My targa top has no rubber so the engine noise flow in when its on. I just don't like the fiberglass top much. Once you weld it in your open convertible days are over.... so I will have to do everything other than the top first. I could insulate my top and tape in on with some insulation added to simulate a hard top, maybe that will give me a good idea as to how it may work..

I would miss the open top on those cool sunny days and those warm summer

nights but it should make it more quiet.

I have the glass installed, used a automotive stick on rubber seal to insulate the two. Cut a peace of plastic and attached it to the firewall, to keep the glass secured. The way it fits really precludes it from falling out anyway. Theres about 1/8 inch clearance just to get it to slip in, once centered it won't come out. I'll drive it tomorrow and see if it's effective. If it is I can bond it in semi-permanently. I showed the glass to my wife and asked her if it looked different in any way, she said it looked cleaner (transparent). Shes not a car person and so this not likely a valid straw pole.

Another way might be to take two rear glass panels and have a glass shop laminate them together with a PVB interlayer, like safety glass. That is a known acoustical deadening technique and not as thick.

From Clayton:

DynaMat works pretty well.

But I have a different idea for you. Neoprene...!!!!

The closed cell structure of neoprene is extremely good at damping sound.

For whatever reason... Neoprene has this interesting quality of damping sound from about 240 HZ to 20K Hz+.

I have used it many times to dampen automotive interiors back in the IASCA days of car stereo competition. You can buy 2X3 foot sheets at AAA yardage in Santa Ana on main street. (if they have it in stock) Call first.

You apply it with 3M Super 77 spray glue. I think it would work really well behind the back pad, headliner, foot wells and floor boards.

When used in conjunction with DynaMat or one of it's derivatives. It works extremely well.

AS far as making a steel top for your teener. My only fear would be snapping your windshield from body flex. The windshield pillars aren't fastened very well to the body either IMHO.

If I were to do this. I would fill the pillars with sprayed in structural foam in an attempt to keep the pillars stiff. That goes for the sail panel pillars too. As a byproduct of this stiffening, You will also incrementally help keep the sound down.

My thinking is to transfer the pillar flexing to the attaching point of the pillar and the body body and your proposed steel top.
In hopes of keeping the flex away from the windshield support surface. Hence keeping the windshield from twisting. This would only be an incremental fix. Yet I think it will help. I forgot something... Is your windshield fastened with Mastic or do you have the vinyl strip holding it in?????

NEXT:

Here is bit of what I know about sound deadening for automotive use.

There is no one single solution. It takes several different materials to get a car's interior quiet. It takes time and knowledge. And it is a lot of work if you want to do it right. It takes lots of little things to make it work.

One of the first places to address in a car interior is any HOLLOW spaces. As they act like a speaker cone. Hollow areas not only pass sound. They also create/transfer audible sounds on their own. It's called sympathetic transfer.
These spaces will pick up all kinds of harmonics. Even some you can't actually hear. Then transfer these harmonics up or down to an audible level. Thus creating even more spurious sound waves in the interior of the car. Fun stuff. isn't it......

MORE:

The basic trick of light weight sound dampening..... Is to put as many air bubbles that aren't touching each other. Between the sound emitter. And you ears.
The bubbles then transfer the sound energy into the binding material and bounce the sound around within each bubble... This creates sound canceling as each harmonic of the sound wave hits it's own sound wave within the bubble. Instant canceling of sound...
Where does all this sound energy then go..???

It turns into heat. The heat is radiated away by the binding material into atmosphere.

Mastic style sound dampening like Dynamat works differently. It simply slows down the harmonics and absorbs the sound. Then returns the sound as heat. It works well at higher freqs. I don't like DynaMat alone for sound below 200H z. Closed cell deadening material + DynaMat works better for that for in MOST applications.

I would love to take your car to high end sound shop and throw it on a Stereo Real Time Analyzer (SRTA) and look at the waterfall plots. That would tell us EXACTLY what to do. Problem is... DUH... We would have to have your car on a rolling road Dyno to accurately do this.....
That would be very interesting from a scientific perspective.....
(that was dream sequence #592)

Sound canceling and heavy weight sound dampening is a subject unto itself. Thats for another day...

SO:

Since you have SO MUCH horse power. I am guessing that you don't mind adding another 20-50 pounds to your car for optimal sound quality.

I have been quieting cars interiors for years. I'm pretty good at it.
NOTE: All of this will cost you weight if you want it as perfect as possible.

Swing on by the coffee house and lets chat about it. I want a ride in your teener anyway... I also want to check your ride quality as per our last conversation.

I also have a notion for using FOX dampers which may well help your ride quality. I am not the first guy to think of this or do it for that matter.
At least you would have optimal adjusting to make your shocks dampen any way you choose on both rebound and compression.
And I have a FOX SHOCKS WD that wants to work with me.

If ya want to chat further with this knucklhead.....
PM me for a phone number.

Regards,
Clayton

Cool idea.

Please take some photos

Clayton,
Sounds (no pun intended) you know something about the subject. Why hasn't anyone filled the longs with structural foam and seal it up ? I thought why not polyurethane, something with some give not a solid, that would surely suck up a lot of vibration. When I had my TT Rx7 I made a lot of my own bushings using that material, but it was a 90 grade a bit too hard. I don't care a bit about weight.
and another thing I saw a Nissan Maxama in a junk yard a few weeks back which had a, if I am remembering correctly, steel rod coated with rubber real thick which was in the trunk area over the rear wheels, I am sure its for vibration control, anyway surely was pointed out via an expensive vibration device Nissan has... Ill PM ya in the AM
John

The biggest FEAR over using foam in the longs is WATER = RUST.

Foam is a sponge. And once it's in there... it is a bit difficult to get it all out.

If I had street car or a race car that I was DAM SURE POSITIVE wouldn't see water.

I would do it in a heart beat.

And that is the inherent problem with ANY material that will absorb or hold water underneath it's membrane. RUST.

Thats where sound deadening becomes an issue that needs caution and knowledge.

Clayton