I know part of my noise issue has to do with what kind of driving surface I'm on. When its slick asphalt, car is pretty quiet. An exposed aggregate road, it gets pretty noisy. Granted this is due to the tires, but I'm probably at least a year away from replacing my tires. I've also checked air/nitrogen pressure and its o.k.

So what I think I want to do is to find a product to put over the spare tire to and then a larger single sheet to put behind the rear seats. My thinking there is that the spare tire compartment probably isn't as well insulated from noise as the rest of the trunk, and then behind the back seat to reduce the overall noise from the trunk.

I'd be interested in other areas of the car if it doesn't involve tearing things apart too much.

I found this product and would like to ask if its appropriate for what I'm trying to do.

http://www.b-quiet.com/vcomp.html

 

I've done a lot of research on this... The very best out there and what I use is Second Skin Damplifier Pro and a layer of Second Skin Luxury Liner Pro to reinforce it. Tests have shown it works better than Dynamat Xtreme, RAAMMat, FatMat, etc etc. It's pricey, but might as well do it right the first time. I did my whole trunk and parts of the inner rear wheel well. If you look at under the spare tire, you'll see that it's just a plastic floorboard with no built in sound deadening material (like the rest of the car). This was the culprit for me for the excessive sound.

 

Thanks for responding.

I can google it but is there a distributor that you had good luck with?

So did you put the material under the tire or just lay it on top of the tire(or possibly under the entire trunk floor?

 

http://www.secondskinaudio.com/

You can talk to Ant and see if he's willing to work out any discounts. They're a direct seller. They've also got some videos on there giving you an example of how it's done. I'd pass on the blade and roller though, you can get them cheaper yourself at Home Depot or Lowes.

Damplifier Pro is used to reduce vibration noise so it needs to be attached to actual surface. Remove everything in the trunk including the spare tire. Make paper cutouts to get precise shapes and less waste of the actual sheets. The sheets have adhesive to them already so it's just a matter of cutting, placing, and using roller to push out any air bubbles. The more surface you attach this to, the less vibration you'll have.

Luxury Liner Pro is used to deflect and muffle any remaining road/exhaust noise that might come through that Damplifier Pro doesn't deflect. It's basically this ultra dense foam mat that you place on top. You'll need to cut a small hole in the middle to fit the spare tire screw through. Then it's just a matter of using aluminum tape and sealing the edges.

You don't want any of this over the spare tire as once it's in, you don't want to remove it. Also you don't want to put it outside underneath because the foil on the damplifier pro can get torn up easily by road debris.

Start with just doing the trunk area by the spare tire and test it out. You should notice a big drop in road noise. If it's not enough, move to inner wheel well and trunk door. If still not enough, move to front and rear doors. Finally if you want tomb like silence, hit up the floors, but this is a very tedious task and not for the faint of heart.

I bought the bulk pack of Damplifier Pro and still have about half the box left which should be enough to cover your trunk area if you want to buy from me.

 

Rear trunk floor, spare wheel well & rear wheel arches. Maybe under the rear seat.

Dynamat is just fine. Remember the chain is only as strong as the weakest link. If you do a better job of isolating the trunk than Benz have done in the rest of the car then you will hear the next loudest noise. NVH engineering is a very precise science. If you make the car too quiet you will find the diff, engine & exhaust are the most irritating noises.

So be realistic. You don't need to **** a fortune at the wall to damp the trunk.

 

The next loudest noise will at the very least be less decibel than the first offender though. It does turn into a hunting game, but with each kill, you reduce overall decibel.

Adding sound deadening, isn't just to cut out exterior noise, but also to reduce music interference, improving sound quality. Nothing kills it more for audiophiles than when your music frequency hits that contrasting noise pitch causing inharmonic wave oscillating effects. You'd have to do the entire cabin though to come anywhere near studio quality silence (not going to get same level obviously).

Knocking around the interior of the car though, the main offender is the spare tire trunk space. That might just be all you need to get rid of the road noise.

Be aware however that you will be adding weight to the car putting this material on. Each sheet is negligible, but combined, you're adding a decent amount of weight. That's the trade-off.

 

What world are you in that the sound of your engine is an irritating noise?

 

Yep ! I understand acoustics - See my profile.

 

Yeah agreed - just an illustration.

 

And please good folk - If you choose to damp your doors, use a bitumastic anti drumming pad or similar that does not retain moisture. You do not want anything that promotes rust.

 

Adding a thick black boot carpet protects the boot floor of of all incoming dirt + adds to sound deadening insulation.

Any sound deadening material should be sealed so not water absorbant to protect against rust . Inspection of direct contact to metal points recommended. Remember that wet muddy flat tyres will at some time be slung into wheel wells & may stay there for periods.

 

Any thoughts on skipping the whole lining the trunk approach and go directly to putting some sound absorbing batting behind the back seats? What I had in mind is one of those cotton bats that's two or three inches thick.

 

Could help. I suspect a fair amount of noise gets through the rear parcel shelf however.

 

A nice and productive Sunday afternoon!

About four hours and a definite appreciation of jigsaw puzzles is needed! It's not the prettiest work I've seen, but under the trunk floor, I'm just hoping its effective. If anyone else wants to do this, find someone else with whom to share the box of Damplifier Pro. I bought Azn300's remainder...did the whole underfloor area, and still have several sheets left.

 

Nice job - let us know how well it works after a few days of car use.

 

So how's the noise difference? Was it worth the effort?

 

I promise I will report, but believe it or not...other chores kept me at home today.

 

Remember, this only is supposed to reduce vibration noise, not all road noise. More of a stage 1. Stage 2 would be adding luxury liner pro which deflects. Great work though. Yeah, it's not pretty, but it's covered up, so who cares.

 

Looks good but does indeed look like a lot of work. Would spraying somethings similiar to Rhino Lining work well as a sound damper? It seems like the thinkness and type of material would, at the least, dampen the metal if not physically block the sound as well. I remember spraying a few old cars with the body undercoating and as more of a side effect, it did seem to reduce the noise.
Do you guys think any type of spray on material would work?

 

I bought some of the 2" accoustical cotton sound insulation material to install behind the back seat. It should be coming in any day. Looking forward to seeing how that works out.

As part of this test, I think I'll rig up my laptop so that I can take some sound level readings. If I can figure out how to do it, I'm going to try to measure what frequencies are the most offending ones and then find what accoustical material from a home theater standpoint is recommended to kill those frequencies.

 

Now you are taking matters seriously. If you go this route you will need a reasonable mic. The one in a laptop will not do. The one in a good old Radio Shack sound meter is just about good enough though it falls off badly at very low frequency. You'll need frequency & DB A weighted at that frequency.

You might be able to download a cracked copy of Sound Forge or similar/more appropriate software off the internet to help you.

Good luck & let us know what you find.

 

Glyn

I've got all kinds of toys for my home theater frequency analysis. Problem is that my testing microphone preamp is one of those that requires an A/C plug. I may have to go the route of using the Radioshack SPL meter with a correction file. I typically use REW (room equalizer wizard) but not familar with its function to take these types of measurement. Need to do a little research there.

I read somewhere about Mercedes having that bank vault quiet. That would be good to aspire to.

 

Ah! Sounds like you have all the kit. Good stuff. I have access to full room acoustic measurement kit but it too is mains powered. I have a totally linear SPL meter that was produced by Infinity a number of years back to make up for the failings in the Radio Shack unit but the darn thing needs a powerstation hanging on the back of it. It's supposed to be dual power but it won't even go 15 minutes on a set of batteries. In fairness the Radio Shack article is about 5% of the price.

 

Ok, I'm sound engineer at a worldwide consulting office. Coming weeks I will try take a professional IEC 651 class I sound measuring device and measure at a standard speed on a part of the highway. I will report the sound levels in 1/3 octave over the audible spectrum. Hope you guys can do something with it.

 

laguna,

Sound like a plan.

When taking your measurements, try to find a rougher texture road. Not talking potholes or cracks in the road, but highway that may have been down for quite a while that has a rougher finish.

Is that 1/3 octave smoothing or measured at 1/3rd octaves?