Sound Proofing

[Robin]

Hi Friends,

I hope everyone is staying safe and well.

I thought some may be interested in this and that it may provide some sort of distraction.

My concept of a stripped out road going car has gone well. Except I cannot stand the noise anymore. Mainly engine noise.

I am not expecting even to be able to make a phone call in this car - but I need to reduce the noise to a tolerable level.

I tried a layer of sound deadener (bitumen) in the engine compartment, with a thick foam/loaded vinyl engine pad but it is still too loud.

So I am biting the bullet and adding sound proofing inside.

Staring point was painted interior with seats and RS rubber mats - nothing else. I do not have a good photo but the rear behind the seats is just paint no trim at all.

[Robin]

Sound proofing seems to be in 3 stages.

Most of what I leaned is available off the internet - these videos are a good resource https://www.youtube.com/watch?v=sSZTgO9msFI

First step is sound deadener - this does not block sound it just stops the panels ringing like a bell/drum when vibrated. Most people cover the entire panel but in theory you only need to cover 20% of big surfaces to stop the vibrations. I want this car to remain light so I am going minimal - all will be a balance of noice reduction to weight.

The deadener is the bitumen based sheets available from many brands.

Sheets weight 0.5KG each (will vary with brand) I used 4 sheets internally. I also used 4 sheets in the engine compartment (across firewall) - I completely covered firewall to block heat and sound - probably should have just done patches.

I did not put on the internal fire wall as engine code is covered.

I also added small patched across inside of door panels.

These sheets can be cut with scissors and you peel off backing paper - stick it on and roll down with a small hard roller.

So this step has added 4-5 KG to the car.

[Terminator]

Currently I am enjoying the symphony from the ST but one day in the future I may reach the same point as you

ST has close ratio gears 1-4 but pretty normal 5th...it drones a bit too much for my liking at legal freeway speeds.

[Oldskl60]

Thanks for sharing Robin. I will be interested in your results. Do you find the engine noise from induction, motor or exhaust... Or all of the above!?
What muffler and engine/gearbox mounts are you using?
Cheers Tom

[9er]

Thanks for sharing Robin. I will be interested in your results. Do you find the engine noise from induction, motor or exhaust... Or all of the above!?
What muffler and engine/gearbox mounts are you using?
Cheers Tom

My 2 cents.

I have dynamat plus factory style sound dampening and the correct engine pad.

I have experimented with Wevo engine mounts using both the black and blue pillows, also poly mounts on transmission.
I have finally decided on factory sport rubber mounts all round.
Nice NVH balance.

Car has a vey sporty sound inside the cabin but that is due mainly to the induction noise from the Weber set up, with K & N sport filters, which is perfect for blasting around in the hills or driving to work.

For interstate travel I would refit the original airbox which dramatically reduces the noise level inside the cabin.

[Robin]

I am running a 2.0L engine with webers and the std airbag with a paper filter.

Exhaust seems relatively std. It is what came with the car - std heat exchanges and rear muffler - although single rear pipe seems larger than std. Does not drone but is not quite.

Noise is a combination of induction/engine/exhaust - Not a bad sound at all but a lot of it. Also I get a bit of tyre/road/stone noise but is covered mainly by the engine noise.

Engine and transmission mounts are all std rubber - WOULD anyone suggest a change of these to make it quieter? 9er suggests std is best.

[Robin]

STEP 2 - is a foam spacing layer. So far I have just added foam to "level" out areas so that the finally foam/vinyl layer will lay flat and look better.

[Paul Ford]

I need to do something with my car as well.
Short drives are fine but anything over 1/2hr is painful. My 5th gear drone is really bad . I'm thinking of getting heavy rubber backed removable carpet sections that I can fit when I don't want to damage my hearing. I went to so much trouble and expense to get the interior as smooth and clean as the exterior I don't think I could bring myself to put bitumen gunge back in.

[Robin]

Paul you mentioned thick rubber backed carpet.

The science of sound proofing is the three layers.

1. Is something stuck to the panels to stop the resonance of the panels - the bitumen material is usually used here. You could skip this or maybe try and use heavy magnetic sheets or something removable. But skipping this step will mean a lot of drone and vibration will continue.
2. Is a separation layer - in walls/ceilings this could just be an air filled void - in a car you do not have a lot of space so a layer of foam is used 10mm or so - mine is 8mm. The foam itself does not really block much of anything it just spaces the third layer from the metal.
3. Is a layer of something heavy that can move slightly. So sound comes through the metal. The metal does not vibrate so much due to layer 1. The sound vibrates and moves the third layer - converting the sound to kinetic energy (the movement of the layer). These days the third layer is a "mass loaded" vinyl so a vinyl sheet with a heavy (safe) metal powder set into it. This third layer destroys the sound rather than blocks it. This stuff is heavy - the sheet in my photo below is 1m x 1.5m and weighs 6.6KG. It is foam backed so combines layers two and three for easier install. I think I will add about 2.5 of these sheets for floor and rear firewall so 16.5KG added!
4. You can then cover the sound layers with carpet/vinyl or whatever so that it looks nice. If you look at RS Type carpet you can see it does not provide any sound proofing at all.

Original Porsche trim used the same layers - bitumen stuck on big panels - horse hair mats etc. to create a space and then a heavy vinyl type layer (Lino type material I think).

On the floor the 2nd and 3rd layer (and carpet) do not really need to be glued - they will just sit in place.

On the rear firewall it will all need to be glued - foam to metal - vinyl to foam (already as one in my case) - carpet to vinyl. You could try and just sit the foam/vinyl in place but really it needs to be glued with joins sealed so that sound is all adsorbed and converted to movement - gaps just let the sound come though - sound is like water and will flow via path of least resistance.

[9er]

https://www.carbuilders.com.au/

are a specialist company for car acoustics, worth a look on there, I bought a more modern alternative to the sound deadening on the roof turret (underneath the headliner)

[silbere]

A few options there, we sell a product AcoustaMat made by " a1 rubber " in Queensland, yes Australian made.

Check them out on a1rubber.com. ,good garage solutions too and you can buy direct .

Recycled rubber and cork in four grades , designed originally for floors in high rise buildings to meet foot fall sound transmission rules between floors, even have fire certificates.

I showed it today to a local respected restorer who is currently working on a RHD conversion 2006 Ford Gt40 ,and he has an application for it.

I don't know if many of you guys have seen these things in the flesh but they are totally awesome in build , tech, and that supercharger view from the rear view mirror is something else, makes an R8 ,Ferrari rear view look ordinary, was in the Gulf colour scheme too

[Robin]

https://www.carbuilders.com.au/
are a specialist company for car acoustics, worth a look on there, I bought a more modern alternative to the sound deadening on the roof turret (underneath the headliner)

Agree - this is where I bought my materials - they are easy to deal with and deliver very quickly. Seems well prices compared to Dynamite etc. products.

[Robin]

I have all three sound proofing layers in.

loose loaded vinyl/foam floor mats on main floor.

Glued foam/mass loaded vinyl at rear. The idea is to create a sealed barrier of the mass loaded vinyl so that sound cannot leak through any gaps. All joins were overlapped by removing some of the foam from the back of the vinyl or cutting stips of vinyl and glueing over joins.

I had some mass loaded vinyl without foam on the back from another project - I used this over the very curved areas - layed foam down first then glued this vinyl. Next time I may use all seperate vinyl and foam as the seperate vinyl is much easier to curve and fit than the stiffer vinyl/foam product (all from car builders linked earlier).

I made some cardboard templates for complex areas then just drew around and cut vinyl with a Stanley knife - this mass loaded vinyl blunts the blades quickly so have plenty of spare ones.

Just by starting the engine with the car still in the garage I can tell this is MUCH quieter.

Before I would put my hand on the rear seat area and fell the whole car body vibrating - now I can barely feel any movement. This process really works well.

I used just under three sheets of the vinyl/foam plus a bit of seperate vinyl - so I would say 18 KG added. (One sheet is for the floor mats which can be easily removed and I guess would mainly help with road noise - not engine noise - so I may remove these after some driving tests).

So 5KG deadener and 18KG foam/vinyl - 23KG added.

I was set on having a light as possible car - but the reality of driving such a noisy car on the road does not work for me.

Carpet next....

[9er]

Hard for my old eyes to be sure but it almost looks like you have front and rear window in, but not headliner?

[Robin]

Did I mention light and stripped out? Yep started with rubber mats and a dash pad. Only adding essential items for sound proofing.