Road noise

[Davezj]

I know there have been a couple of other threads on this subject in the past but I am asking a particular question.

Where does the road noise come from?
From the tyres, up through the suspension arm, and shock, along the front chassis rails up to the bulk head and then into the cabin.

How can you stop the noise getting into the cabin?
There is always the noise dampening matting material that car be applied, but that is curing the simptoms and not tackling the cause.
Now as I see it the suspension arms are quite well isolated due to the rubber bushings in the mounting points.
But the shock/spring strut does seem to be a good culprit for transmitting noise, as there does not seem to any bushing to stop the noise. There is the rubber seat on top of the spring and there is a rubber mount on the top of the shock but if they are not doing there job properly due to old hard rubber.
So here is my point eventually,

Can you isolate the top of the shock mount by fitting some kind of gasket between it and the mounting point on the car body.
Maybe a PTFE, foam, leather or some other material disk a few mm think to stop noise traveling any further and similar type material washer under the nut on top of the strut.

What do you think.

[Wodjno]

Drop Andy(The Vee) a pm. This is his 2nd biggest bugbear when it comes to cars. He has spent pretty much 10 years fettling his car against road noise.


Sent from my HTC Wildfire using Tapatalk

[The Vee]

I cut up inner tubes to the shape of the top plates not long after I got the car. Think I used two layers per strut. Mouted between the strut top plate and body work on all four corners. It seemed to make a little improvement, but of course noise will still transmit through the bolts when tightened down. Now, if you could insulate the bolts as well that would help, but you'd effectively have a floating strut which although only very slight, may not do a lot for handling / geometry.

[Davezj]

I know andy has done a full strip down and sound deadening matting stuff everywhere, I will have to ask him if he did any other stuff.
Thanks for the reminder Glenn.

[The Vee]

LOL must have been typing when you replied Glenn!

[Davezj]

Beat me to it andy.

Yes I had thought about the floating issue, that's why I was considering the use of leather on the strut top and a leather washer under the nut to isolate it.
I would have thought that with the use of leather you could really tighten down on to the leather washers, probably best to trap the leather washer between a pair of metal washers under each nut.

[The Vee]

Sound deadening mats in doors and on floor. Then layer of that course horse hair stuff all over under carpet. Soft trim covering on door cards - that helped more than you'd think. Funilly enough, as Glenn mentioned, it is a real bug bear of mine and only recently have now decided to remove the roof lining and treat it to some soft fabric and probably put mats on the roof itself (inside of course)!!
Tyres make a big difference - but just which are the quietest - I give up! One other thing I have contemplated is those metal doughnuts that stop resonance through heavier metals such as chassis rails and the rear shelf support. Rover / BL used to use them. All of this though does add a deceptive amount of weight. I find the noise less intrusive on the Leggie than the saloon which is odd as saloons are generally thought to be quieter................Overall I'm afraid I put a lot of it down to thin metal used to save weight and costs, plus poor initial sound insulation from Mitsi.

[Davezj]

Now I just need to find some thickish leather, unless you can suggest a better material.

I have just realised where I can get just the sort of leather I was thinking of, a welding apron, that is nice and thick and I can use two layers of leather to ensure the metal washers do not touch each other.

[The Vee]

Yep I can see the leather, but you would also need to make sure the side of the bolt is not touching the hole. Sleeving? Maybe but a very shallow one. You could bore out the holes slightly but you'd need to watch strength plus alignments. Funny, the car is so quiet when abroad - they use that noise absorbent surface far more than we do here.

[Davezj]

The reason that sparked my interest was an article in the Feb edition of evo magazine using the car stereo it output an anti phase noise to cancel out the actual noise.
It was the placement of the noise pickup sensors on the strut tops that got me thinking.

[The Vee]

One other thing I found was that the load spread offered by the top plate is reduced due to compression of the rubber - watch out for that.

[The Vee]

Yes that Idea has been around for a while - never witnessed it but can imagine it should work, but probably quite technical

[The Vee]

By the way, Glenn. What's my first bug-bear?................................

[Wodjno]

By the way, Glenn. What's my first bug-bear?................................

Haha.. You know full well what it is /yes

[WOODY72]

It's all down to the bloody asphalt they use on various road surfaces as you well know, and in my opinion, there isn't much you can do to stop it. Granted you can use a different make of tyre, but all the manufacturers claim that their "new" tyre is the quietest ever!!!! Sound deadening will help to a certain extent, but i think it's turn the radio up or live with it!

[The Vee]

Haha.. You know full well what it is /yes

Yep!!!! now where are those new arches? /pan

Back on track, Graham - there's a lot of truth in that, but the G has always been a little excessive for me. Tis a lot better now to be fair, but other cars can do a lot better job in this respect.

[Davezj]

i think PDF's take a while to come up in a thtread, well mine do.

50621

[Davezj]

One other thing I found was that the load spread offered by the top plate is reduced due to compression of the rubber - watch out for that.

what do you mean by load spread.

is it a the spongyness of the rubber you are talking about.
that is why i thought of leather as the isolating material

[The Vee]

because the rubber compressed more under where the bolts tighted the top plates flexed slighty between the bolt holes therefore the weight of the car was more taken in the areas around the holes. Without the rubber there was no flexing, so load distribeted evenly. Only slight, but it was there.

[Davezj]

It's all down to the bloody asphalt they use on various road surfaces as you well know, and in my opinion, there isn't much you can do to stop it. Granted you can use a different make of tyre, but all the manufacturers claim that their "new" tyre is the quietest ever!!!! Sound deadening will help to a certain extent, but i think it's turn the radio up or live with it!

yes the road surface is the main reason for high road noise. but wide tyres will be much worse than skinny ones. but we all love wide tyres.

[Davezj]

because the rubber compressed more under where the bolts tighted the top plates flexed slighty between the bolt holes therefore the weight of the car was more taken in the areas around the holes. Without the rubber there was no flexing, so load distribeted evenly. Only slight, but it was there.

right gotcha!

maybe i will try a double layer of leather and possibly a third layer round the bolt holes to even out the pressure. then a double leather washer in between a pair of metal washers under the each nut on top of the strut.
seems like a plan.

i have a db meter so i can actually do a proper test a before and after test on a couple of different road surfaces and a couple of different speeds.
i will have to find a noisy surface to give it a good test.
unfortunately my exhaust is very loud so i don't know if that will drown out the road noise or not.

[The Vee]

Dave, one of my other "projects" was to have metalastic mountings made up. If you know the old BL engine mount types these were basically rubber sandwiched between metal plates and all bonded together. This would invove the two plates having bolts fixed in pointing up and down. Then removing the bolts from the strut top plate and tighteng the new bolts from underneath and the top bolts as normal. But it was flawed for a number of reasons, ride height would raise (although coilovers could relieve some of that) cost would be prohibitive, there used to be a factory near here and no real failsafe should the bonding fail. Don't forget that the top arms may well also transmit noise as they only have rather small rubber bushes. A problem eliminated if I ever do my USDM conversion!! Now that's all my bugbears revealed - remember the lower swivels? !!

[Davezj]

see what you mean, by the doughnut mount, but as you say it is not fail safe.
sound a but like the compliant mount lotus used to use on the rear drive shafts on the elan, a rubber doughnut bolted through from either side. but that was used more for flex compliance.

[Wodjno]

unfortunately my exhaust is very loud so i don't know if that will drown out the road noise or not.
Let off the gas?

[Davezj]

yes that would be an option, simple is best!

[Wodjno]

yes that would be an option, simple is best!

I do simple very well :vulcan:

[Erskine_atom]

i will have to find a noisy surface to give it a good test.

Try the A90 southbound from Aberdeen. It's hellafa loud!

Might be a bit of a trek but you'll be passing my house where I'm sure I could make you a cup of tea!

[Davezj]

yes A90 is a bit of a trek for me.

[Davezj]

there is a bit of really noisy road suface on the M6 when going south round birmingham way i think it is so noisy it is unbelievable it sound like all your tyres have just burst and your running on your rims.

[scc]

I find Lexus dead quiet. What do they do?

Otherwise, I find softtyres make an improvement.

Cheers,
Scc

[Davezj]

so what is the actual path of the noise from tyre to cabin, i assume there are multiple paths.

here is a nice bit of info about choice of sound deadening material and why it is used.

http://www.roush.com/Portals/1/Downloads/Articles/AutomotiveSoundAbsorbing.pdf