under bonnet sound proofing

[billythefish]

I was wondering was it worth putting sound proof insulation ( fire proof ) under the bonnet and around the bulk head just to dampen the engine sound down a bit.
The wife loves the car but she reckons it reminds her of a tractor, only thing I would worry about is could the engine compartment become too hot and overheat the engine?
billy.
Yes I am still alive and trying to fix my Rover 75 clutch for the past week but I've still got the good old R4 to take me around on my travels.

 

[reidalpine]

Hi billythefish! You might mount some fireproof sound-dampening material on the firewall .plus some pieces under the bonnet/hood. You don't have to cover all over as dampening-material are just to get rid of the "parasitic" resonances made by the panels..
Some pads on the inner-wings Plus some softer exhaust-mounts would also help.
Inside of firewall (front of footwell)can be covered too.Your best bet here would be the heavy asphalt-stuff. Inside of A-panels is another place I would check out.Also make sure the exhaust-pipes are free to move and do not rub against panels etc..
What you want is to stop the resonances going from panel to panel and get amplified by these. -R.

 

[billythefish]

sound proofing

I will follow your advice and see what happens,I have already done inside the door panels which did help a little but the main area of contention is the noise from exhaust, there is a small leak where the exhaust pipe connects to the box itself however, no amount of tightening up the U bolt stops the leak, so I might just resort to welding it together for a tighter fit.
Thanks for the info -R
Billy

 

[reidalpine]

Billy! I used 50cm of exhaust-bandage on the joint and since that it has been totally quiet.Just wrap on tight and use a bit of steelwire on to secure it.
Next time I have to do something in the exhaust-department I will enlarge the round hole where the pipe goes into the inner-wing so the problem of sagging down and touching will be remedied for good.Also makes it easier to fasten up the clamp and gives better airflow too..
-Any panels overlapping or joined by screws/clips will also benefit greatly from having some rubber-grommets pushed in-between.
The larger the Total surface of panels the more they resonate and the more noise they will give..
-All the best Billy! -R.

 

[malcolm]

My own approach would be first get the joint sealed. The quality of exhaust fit is variable these days, but a load of exhaust assembly paste ought to do the job.

Second is to seal holes between the cabin and engine. Any grommets that don't fit properly, unblocked holes or that main wiring grommet.

For choices of soundproofing, normally you would absorb sound in the engine bay with that felt-like material with the black felt surface. That reduces noise level before it gets a chance of entering the cabin. Something like the "sound deadening felt" on http://www.woolies-trim.co.uk/c-126-felt.aspx That can go anywhere, towards the bulkhead is best. I reckon it's ugly.

From there reducing transparency of the bulkhead will be helpful. Damping material will do this but will result in an increase in booming. The other option is a heavy layer/foam that tou would cover as much as the bulkhead as possible on the inside of the car with the foam part against the bulkhead. Like this: http://www.soundservice.co.uk/SAPT220_foam_absorption.html Coverage needs to be good.

 

[reidalpine]

Hi Malc! being on your home-pitch c",) here, I'm not sure how much relevance my tid-bits would have..
-As I see it, we're talking about 2 aspects of unwanted sound/noise.
One being Direct sound and other being Reflected or resonant sounds right?
Best approach would possibly be to kill sound/noise At the source which at best would be difficult on it's own, so my best bet would be a combo of the two-to kill noise at the source Where possible -Then try to dampen Resonances with some heavy dampening-material.
I've used both aspaltine-mats where I could get to stick and the thicker stuff laden with lead-pellets to get rid of(some)of the parasitic resonances(mostly the higher pitch I guess)transferred by the panels
Direct noise would require an All-covering approach whereas resonant noise would be effective where part of the panels are covered so as to "break" and dissipate soundwaves. Right or wrong?
-My theory is that as both the R4L and the Fourgonnette has the same source of noise,but usually the vans are noisier, this can be put down to more and larger 'naked' resonnancing panels
What say the Pro?
-seems to work pretty good in Roffen anyways... -R.

 

[malcolm]

I've never actually attempted to reduce noise level in a R4 before so I'm guessing a bit.

An engine will generate noise in 2 ways:

First is structure borne noise: vibration transmitted through the mountings into the car structure will excite the panels around the cabin which radiate into the cavity. This might be booming noise or mid frequency noise (general racket that makes it difficult to hear people speak).

The Renault 4 panels are very thin so have a fairly high primary resonant frequency. Adding damping to them will reduce general racket but increase booming as the extra weight will reduce the resonant frequencies of the panels.

Second is radiated noise from the engine (the stuff you hear when standing beside it). This finds it's way into the cabin as airborne noise through holes, and also directly through steel panels and glass, much in the same way as light would pass through something that is very slightly transparent.

This noise tends to be mid to high frequency. Good sealing is very important. Noise absorbing materials (felt or open cell foam) can reduce the source by stopping the noise from bouncing backwards and forwards in the engine bay, and also it can be very effective inside the cabin - stopping noise bouncing around in there once it's made it in. It will give the feel of the car more of a "dead" character than a thin tinny rattly character.

For noise radiated off the panels (whether the panels are directly excited by radiation of through resonance in the structure) Damping can be very effective, but it takes a lot of development to work out where to put it without causing the panels to boom.

To stop noise radiating off panels they need to be prevented from exciting the air inside the cabin. A sheet of rubber held off the panel by foam will not radiate nearly as much noise in as the panel by itself. The R4 floor covering is already rubber, so a bit of foam underneath the covering works well, just leaving the bulkhead to tackle.

For less technodrivel and a bit more practice see http://www.renault4.co.uk/gordini-soundproofing.htm It's not on the road yet so no testing.

I've yet to decide how/if to treat the bulkhead on my project. I'll get the car on the road and do a bit of testing to see if I think it would be nicer with something on the bulkhead.

 

[reidalpine]

So there we have it-Right from the horse's mouth (all pun intended!)
-How about you starting a special-edition For R4's only of that counter-
or opposite phase system we discussed this last summer Malc?
Same one they have implemented in some Lexus'es and that both Koss and Sennheiser now have made widely avail.working off a 3V.chip
What does it take? 12Volts supply-Which we have. A couple of mikes connected to a small in/out amp Plus 3-4 speakers..and Hey-Presto we have practically no noise at least where the human ear is most sensible...
This would make the perfect Christmas gift for all R4-owners -plus you would get filthy rich Malc!
-R.
PS: my friend had a high-pitched noise-problem coming from his rh-side,but
soon as his wife stepped out the terrible earwrecking noise went away too......

 

[billythefish]

soundproofing

Once this rain stops I might attempt some of the good ideas you guys have come up with.
I also found out today that the floors in the front were covered in water, no doubt the guy that sprayed it decided the easy method was to take the windscreen out and never sealed it when he refitted it.
Another day and yet another problem, but life still goes on and soon it will be Christmas and I will be able to open all those presents that I don't really want or need, the woolly scarf, the woolly socks and the woolly jumper, no wonder those poor sheep look like they are freezing to death in the fields when I pass bye.