Reducing the level of noise : need tips to get the best weight/result ratio

[GGR]

Hi all,

I'm coming from the MB side of Pelican but I'm here because I think the Porsche guys may be the best to answwer my questions.

I have a '62 W111 Coupe (see picture below) that I have extensively modified using the MB parts bin while retaining the original look. I have Megasquirted and fitted a euro 5.0 M117 motor (AMG camshafts) with a 5 speed manual trans and uprated rear end, brakes and suspension. I have also ditched all the heavy stuff like aircon, sound deadening etc. and replaced all iron parts with aluminum ones where I could (engine block, wheels etc. The car weights 1400 kg (still working on it) and the engine is 300 hp. This is less than 5kg/hp which is where I wanted to be as my original plan was to match the GTs of the era, like Facel Vega, Iso Rivolta and some Maseratis.

The car is now driving beautifully, but halas, removing all the 50 years old and crumbling sound deadening material has incresed the level of noise and vibrations in the cabin to a level a bit higher than one would expect when driving in a Mercedes. So I need to compromise, and put some of the sound deadining (and weight) back in the car. I looked on the web, and all I found was oriented towards music, and weight was not a concern.

So here are my questions. I would like to get the most efficient way to lessen noise while adding the least weight possible. What is the best material I should use ? What are the best techniques? (combination of materials) I read there was no need to cover 100% of a panel to get a good result. How much of it should I cover? How should I apply/place the material ?

I'm sure you Porsche guys have looked into that as weight is a concern on sports cars.

Thanks all in advance for the help !

[gestalt1]

Many years ago my dad and i restored a jensen interceptor, we spent a lot of time using newer tech sound insulation to block the engine heat and lower the volume of the exhaust. What we found is thaere are 2 ways to lower the sound, cut the panel vibrations and second to lower the vibrations from getting into the interior. Adding a dense asphalt type layer absorbs some vibrations and converts them to a little heat and basically lowers the frequency of the sound waves so the volume seems lower. You only need to add it to the middle of larger panels such as the roof, floor, door skins etc. Not all surfaces need this. A good idea is to use spray on truck bed liner in the wheel wells, underside etc. This will provide the panel vibration high frequency absobtion and also protect the underside from road grime and rocks. The next sound block is to cover the interior completly in a light foam sheet with a heavy vinyl top surface. This actually lowers the volume of the sound but is heavy. It works because the foam absorbs the vibrations from the panels and the heavy vinyl suface does not transmit the vibrations from the foam. This material is heavy and is typically put everywhere under the carpet. I would recomment adding the ruberized undercoating or truck bed liner first to see if that works well enough. A gallon of the stuff weighs about 15lbs so you are not adding much weight.

[GGR]

Thanks !

Indeed undercoating is a good idea. I took all the original one off because it was peeling. I treated all the surfaces with POR-15 so i guess now it's ready to receive a layer of undecoating.

I also read that most of the noise on front engined cars is through the firewall (obviously) but also through the hood/windshield and then also reflected by the road back through the front floors. Add to that the noise of the diff and I'm left with dealing with the whole passenger compartment.

Thanks again for the help.

[Uwon]

Hi Guys,
Read the thread with interest as it applies to my project 911.
Where do you get the " light foam sheet with a heavy vinyl top surface" that gestalt1 mentioned? Would you have a web site or make?
Thanks in advance.
Cheers,
Uwon

[gestalt1]

I don't remember where - this was 10 years ago. I'm sure a web search will turn up some options. I was merely describing why and how sound deadening material works.

Also keep in mind that no matter how much sound material you put in the glass windows are a major problem. They let most of the sound in and they are at ear level. Modern luxury cars use dual pane glass which helps alot.

[pontifex4]

Beautiful car!

This is the premium sound barrier product: Luxury Liner - Acoustic Noise Barrier and Insulation Barrier

This is the inexpensive alternative: B-Quiet sound deadening materials - B-Quiet Vcomp

Both are heavy, and do nothing to quell vibrations. For that, you need a viscoelastic damping product (30% panel coverage is normally fine) such as: Damplifier Pro - Automotive Sound Deadener CLD Vibration damping mat - See what all the fuss is about

or: B-Quiet sound deadening materials - B-Quiet Ultimate - Better than Dynamat!! brownbread

As a rule, use your knuckle to determine where to put the adhesive damping material -- it sticks on, so just knock on the panel to find resonance, then knock again with the thumb of your other hand putting some pressure on the panel near where you knock. If there's a significant difference, stick a tile there. If not, move on.

Undercoating will help, too, especially with rocks and road grit noise.

You're welcome to PM me for more information.

[GGR]

Sorry for late reply.

Thank you very much. This is very helpful. I will surely contact you once I dive into it.

[PcarPhil]

Originally Posted by pontifex4

Beautiful car!

This is the premium sound barrier product: Luxury Liner - Acoustic Noise Barrier and Insulation Barrier

This is the inexpensive alternative: B-Quiet sound deadening materials - B-Quiet Vcomp

Both are heavy, and do nothing to quell vibrations. For that, you need a viscoelastic damping product (30% panel coverage is normally fine) such as: Damplifier Pro - Automotive Sound Deadener CLD Vibration damping mat - See what all the fuss is about

or: B-Quiet sound deadening materials - B-Quiet Ultimate - Better than Dynamat!! brownbread

As a rule, use your knuckle to determine where to put the adhesive damping material -- it sticks on, so just knock on the panel to find resonance, then knock again with the thumb of your other hand putting some pressure on the panel near where you knock. If there's a significant difference, stick a tile there. If not, move on.

Undercoating will help, too, especially with rocks and road grit noise.

You're welcome to PM me for more information.

Charlie,

Which above product do you recommend (or combination of products) for the back seat area of an aircooled 911 to reduce engine and exhaust volume? Currently I'm running without the stock sound pad and all of the sound deadening in the rear seat area has been removed.

I'd like to reinstall some current technology sound/vibration damper. It doesn't need to be extreme reduction in sound/vibration but I'd like to take the 'edge' off of running without any damping. Ideally without adding a whole bunch of weight.

Thanks in advance for the advice!

[pontifex4]

Originally Posted by GGR

Sorry for late reply.

Thank you very much. This is very helpful. I will surely contact you once I dive into it.

Feel free! That looks like a great project.

Originally Posted by Kaefer

Charlie,

Which above product do you recommend (or combination of products) for the back seat area of an aircooled 911 to reduce engine and exhaust volume? Currently I'm running without the stock sound pad and all of the sound deadening in the rear seat area has been removed.

I'd like to reinstall some current technology sound/vibration damper. It doesn't need to be extreme reduction in sound/vibration but I'd like to take the 'edge' off of running without any damping. Ideally without adding a whole bunch of weight.

Thanks in advance for the advice!

Scott, the sound barrier products I mentioned (V-Comp, Luxury Liner Pro) are very heavy, and really only work well in large, continuous sheets (a full floor, for example).

The best bet is to buy between 20 and 30 square feet of the dampener product (B-Quiet Ultimate is good and is among the least expensive, Damplifier Pro is the premium option, and there are a wide variety of others, including Dynamat though I only recommend the Butyl-based products) and cut it into manageable squares or shapes that you can stick on after knocking on the panel with your knuckle to find the most resonant areas, as explained above. This will make an enormous difference, and may only add about 10 pounds if you use it sparingly.

It's very important to note that more is not necessarily better, and that there is really no reason to use a double layer of this type of product, or even to completely cover a surface.

Also, avoid duct seal, peel-and-stick insulation and other building materials. Those genuinely don't work as well, and in many cases, you have to use spray adhesive to get them to stick. Also, avoid all tar-based products.