Noise insulation, Engineer types opinions needed Options

[vitamin914]

You can attack the firewall problem but in the end the rear window will become the loudest transference of noise.

I think the OEM engine bay rubber pad glued to insulation gave pretty decent results.
I might suggest adding dynamite to the interior of the firewall in addition to the oem engine bay pad, then call it quits.

Rich

Good morning Rich, I did a dual glaze rear window on my 914 almost 30 years ago. Look at the picture below, the identification on the glass is mirrored or doubled.

In fact, right after I put in the 3.2 L motor I ran without a back window for almost a year. Rain does not get into the car when you’re going forward. Lol

Creative - I didn’t realize you can fit two layers of glass in there. How did you secure the second pane of glass?

Modern luxury cars often use thicker and sometimes laminated glass on side and rear windows as a way to reduce NVH. The lamination layer acts like constrained layer damping impeding sound transfer from one pane of glass to the other.

I like the double glazing. Nicely done.

Laminated glass is a good idea too... Lots of high end Mercedes use this trick.

I have a spare 914 b/w that I will need to look at. I think it is basically a flat piece of tempered glass with little to no cross car curvature. You can buy panes of laminated flat glass - doubtful it is DOT rated, but... digitize a sample b/w and drop a laminated blank into a FlowJet water cutting machine - and an instant laminated back window glass for the 914. Of course your would need to mask-off the cut area to prevent etch from the garnet abrasive. I had water jet cutting done on a small 12"x12" piece of laminated glass that worked out well for an industrial porthole.

I am going to have to look into this.

[Bucci]

You can attack the firewall problem but in the end the rear window will become the loudest transference of noise.

I think the OEM engine bay rubber pad glued to insulation gave pretty decent results.
I might suggest adding dynamite to the interior of the firewall in addition to the oem engine bay pad, then call it quits.

Rich

Good morning Rich, I did a dual glaze rear window on my 914 almost 30 years ago. Look at the picture below, the identification on the glass is mirrored or doubled.

In fact, right after I put in the 3.2 L motor I ran without a back window for almost a year. Rain does not get into the car when you’re going forward. Lol

Creative - I didn’t realize you can fit two layers of glass in there. How did you secure the second pane of glass?

Modern luxury cars often use thicker and sometimes laminated glass on side and rear windows as a way to reduce NVH. The lamination layer acts like constrained layer damping impeding sound transfer from one pane of glass to the other.

Yes, you can fit two pieces of glass in the space behind the seatbelt anchor point vinyl interior trim. I used balsa wood as an intermediate gasket piece between the glass, (it allowed minor ventilation, so condensation does not fog up the dual glaze window) I then sandwiched the two pieces of glass together with silicone.

@vitamin914

By the way, I did get the idea after looking at a Mercedes sedan that had dual glazed driver and passenger side windows..!

[Root_Werks]

I had a 914 rear window cut from laminated glass once just so it'd be tinted. Surprised how much noise was reduced. I'll be doing that to my current 914 at some point.