according to what I can dig up, the laminated rear window of the same thickness should lower the sound level between 3 to 4 dbs compared to the stock glass....the same laminated rear window will also be ~5% to 10% lighter depending on brand

no idea on the cost......

group buy???

when you say Laminated, do you mean a product like Plexiglass?

QUOTE (Scott Carlberg @ May 18 2005, 11:58 AM)

when you say Laminated, do you mean a product like Plexiglass?

nope.....more like your front windshield....basicly, it's 2 pieces of glass with a piece of plastic in between the glass....

the plastic acts as insulation and adds strength to the assembly...

the advantage of it over plexiglass is the scratch and chemical resistance....plexiglass would work, but I don't want to go down that path....

Hmmm,

Lami won't weigh less, or be the same thickness. Standard laminated sheet glass is 2 pieces of "double strength" glass on either side of a sheet of very tough clear plastic, resulting in a sandwich 1/4 thick. Tempered safety glass like a stock back window, being a single sheet of glass, while thicker than a single piece of DS, is thinner than 1/4, and should weigh less accordingly. Keep in mind we are probably talking a maximum weigh increase of maybe 3-5 lbs.

I had never thought about it before, but it certainly makes sense that the flexible sheet in the glass would transfer vibration less efficiently, and should reduce noise.

Mike, keep us posted on any additional details that you may come across on this.

SOT: I was reading about laminated glass for houses as an alternative to double pane, looks more factory on a 1912 craftsman, and they mentioned sound deadening as one of the features. You can also use original glass which looks different than reproduction "wavy" glass.

After reading that and once again hearing my wife's favorite 914 refrain "This car's so loud" I had only vaguely started to put the 2 topics together, weird how these things hit the collective consiousness (sp?). I'm going to go crazy with FatMat to damp the noise and rattles, but figured that the window was just going to be as Porsche made it, now maybe not... The weight diff is negligible to me.

I would participate in a group buy, if it comes to that.

Eric

If you guys have legit interest in this, I could make them or get them made at pretty close to cost of the glass (I fix traffic boo-boos. . .. I mean I am "corporate counsel" for my old buds at the glass shop in exchange for cost on glass related stuff).

Shipping out left could be an issue though.

Lam glass is way quieter and its something I want to do so Monique and I can talk when we drive somewhere instead of yelling.

The way that I've heard power/sound pressure in stereos described is doubling your power increases your volume 3db. examples: if 50w = 100db, 100w = 103db, 200w = 106db, etc. My dad's example of this formula used sticks of dynamite for a source...

If that's true, and Lam glass can reduce sound transmission by 3db, that's cutting the sound pressure by half. So how thick can the rear window be and still fit in the stock mounts?

Eric

Since its glued in with Butyl rubber rope it should fit with ease.

Didn't Miles try wire glass?

Do it Mike. I wanna know.

My upholstry guy is into this kind of stuff. He suggested using two rear glass windows with a air space between them. This is supposed to change the sound frequency or something....

I want to space the 2 pieces of glass far enough apart to make a fish tank!

QUOTE (jonwatts @ May 18 2005, 08:42 PM)

I want to space the 2 pieces of glass far enough apart to make a fish tank!

With my bunk head mod I have the space for that. You may need to remove the rear view mirror though. You'd have the tendency to watch the fish and not the road...

I have laminated rear window and I have to say that I have never thought it might lower the sound level. Maybe it is me and my noisy 914, but I think this is

Then, why I have laminated rear window. My original glass was ugly. I went to local auto glass shop and asked them to make me a new rear window from tinted glass. They did it from laminated glass and they told the lower edge of the glass was really difficult to cut. First two glasses they broke during cutting the lower edge.

QUOTE

My upholstry guy is into this kind of stuff. He suggested using two rear glass windows with a air space between them. This is supposed to change the sound frequency or something.... confused24.gif

Two rear glasses with air space between them, this is something I believe. I have heard that this has has been done years ago in germany when our cars were new. I am not sure, but I think the results were good.

QUOTE

I have laminated rear window and I have to say that I have never thought it might lower the sound level. Maybe it is me and my 914, but I think this is  :bullshit:

i've seen the demos at the home stores, I've read the documents on about 5 commercial glass makers (suppliers of laminated glass to the automotive industry)...maybe it's a conspriacy to lie to the general public and to get the car manufactures waste money on things that don't work

seriously, it does work, but how well in a 914 is a totally different story....i have no method to measure the differance except for using an audio recording device for a before and after test....

QUOTE

seriously, it does work, but how well in a 914 is a totally different story...

Yes, I am sure the theory is right. I just dot believe it helps much in our cars.

From the cars that I have driven and ridden in I've noticed a SIGNIFICANT noise reduction from.... the engine bay sponge... er sound pad. It's no good for the metal, but it's good for the ears. I'm a believer.

To bring this back onto topic, I doubt you would notice a laminated window if you didn't have the engine bay sound pad in.

Seems the data should be very accurate for the glass itself. . . 3db reduction, but question is how well it works in the assembly. . . too many things to consider I guess. . . gotta figure out how much of the sound is actually coming through the glass as opposed to chassis, firewall, etc. etc. . .

only 1 way to find out. Couldn't possibly hurt.

QUOTE (McMark @ May 18 2005, 10:58 PM)

From the cars that I have driven and ridden in I've noticed a SIGNIFICANT noise reduction from.... the engine bay sponge... er sound pad. It's no good for the metal, but it's good for the ears. I'm a believer. To bring this back onto topic, I doubt you would notice a laminated window if you didn't have the engine bay sound pad in.

What about leaving the stock glass in place and sandwhich-ing it between two sheets of Lexan plastic. Just add one to the outside and one to the inside..this would take less effort than removing the window and should produce the same effect. Thing this would have any positive effects?

Doug C

Any thickness increase will have a positive effect, but part of the success of laminated glass is the close, tight bond between the two pieces. I would expect a home-brew to be more.... "loose".

I'd be interested...

Hey, I've got two rears now...maybe I'll try to 'sandwitch them and see what happens!





j/k

Someone earlier in this thread mentioned that an air cavity between two of the laminates would be better for sound deadening.. this may be a way of getting that done, at least on one side..the exterior side I would think. Laminate the interior lexan directly to the stock glass then a thin spacer around the perimeter on the exterior side and install the lexan snuggly.

Doug C

If it comes to a group buy on these I may be in for it.

I've laid down double-thick layers of sound-deadening material on the firewall. You'd be suprised how much of the noise really does come through the window. I have a decent-shape engine bay pad too! Still I have to yell on the freeway at times. I can't even talk to my passenger.

The air pocket would have to be completely devoid of moisture, though. Otherwise, you will get horrible fogging inside. I think that you woudl have better luck, and lower maintenence if you laminated two rears together. All you are trying to do is to get hte window not to resonate at the frequency of the engine, exhaust, etc. Higher frequencies. Laminates, I would imagine, resonate at lower frequencies because they have more mass to move.

The problem is you would never be able to do it in a way that would stay clear. You are essentially trying to make a home made thermopane. Thermopanes are made in a very high tech clean/dry room using very expensive equipment and specially designed spacers and sealers to get and keep the interior air space clean, 0% humidity and air tight. Unless you were able to put your entire car in a room like that, even IF you were able to make a durable air tight seal(and thats a really big "if") you will end up with moisture in the air space that will eventually condense out, and fog your window.

hahaha, Mike beat me to it.

If you are gonna laminate 2 widows together, I really think you'd be better off just getting a lami backglass made. I was looking at a back glass the other night, and there is nothing about it that would be hard to cut. I've cut much more complex pieces without trouble, and I was just a run of the mill glass cutter.

I ran without a rear window this weekend.....it's glorius, I'm leaving it that way

QUOTE

f you are gonna laminate 2 widows together, I really think you'd be better off just getting a lami backglass made. I was looking at a back glass the other night, and there is nothing about it that would be hard to cut. I've cut much more complex pieces without trouble, and I was just a run of the mill glass cutter

We are fortunate to have a window with no complex curves. My cousin in PA has a friend that does this kind of thing, but I bet if you called a glass place in your hood, that you would find many folks willing/able to do this. It might not even be too much.

I think that the laminated window will not have much effect if that is the only sound control in the car, but if you've gone through doors, floors and 'walls, the sound through the glass will be a more noticable percentage of the overall level.

I'm still in for a pro prepped solution...

Eric

Aw Hell, you guys ...I never have any good ideas!

Doug C