Hi,
I would like to lower the noise level inside my XKR (coupé), primarily the low frequency exhaust rumble / resonance at low rpm. Didn’t think it would bother me in a X100 model but experience tells me that yes it does, for example when stuck in the traffic at low speed during the rush hours (damaged ears…)

Has anybody done something in this regard ? I’m thinking about sound deadening the trunk floor and spare wheel compartment at first, then the rear seats wall and the panel under the rear window. About this last part : there’s a big hole in the sheetmetal, purposely covered by foam and other material. Is this for acoustical reasons or something else ?

Your inputs are welcomed.

 

An unusual complaint - many here deliberately replace the rear silencer boxes with straight through pipes to make the V8 roar.

In standard form, it should be a reasonably quiet car but you can't expect the same sound levels as an XJ saloon.

If you're getting low frequency rumble, this may be the rear exhaust mounting rubbers worn (items 2 and 8) allowing metal to metal contact:



The hole you describe - is this the space where the rear speaker is fitted in the Harmon Kardon premium sound system?:



Photographed from below in the boot space.

Graham

 

+1 My car is VERY Quiet. Maybe someone modified your exhaust in the past?

 

Hi,

Thanks for the picture of the speaker : I must have the basic system, didn't know that another speaker could be there. The car is not altered in any way and is in near new condition. ANd you are right, it's very quiet averall for this kind of vehicle. It's just that I have developped an hyper sensitivity to low frequencies that give me headaches and tinetis... I used to drive in much louder cars in the past (like 1920's racers) and had to give up 10 years ago. It's the acoustic resonance at low charge / low revs that gives me a problem.

 

Mine is also very quiet when its idling and pottering along with a lovely sound when opened up.I think check your exhaust system first.

Al

 

You could dynomat the rear boot, that should help a little.

 

Both Paul and Al confirm their XKR coupes are quiet and my XK8 coupe is quiet with no vibration or resonance at idle or low revs.

Have you had an opportunity to try another XKR for comparison?

If the exhaust mounts prove to be OK, engine or transmission mounts could be another possible source.

Graham

 

No, no, again the car is absolutely fine, it's just my over-sensitive ears... Graham, the 4.2 normally aspirated is quieter than the R, without the "deep" note that I'm talking about (note that I like though, but it hurts me in the long run, too bad... )

 

I'd use what Avos has suggested and Dynomat the car, inner wheel arches in the boot and the rear upper seat panel. This will quieten down any low resonance.

 

Yep Sean. I did a little bit of reading since my 1st post. Seems that the right thing to do is first to apply a "mass" layer such as Dynamat for vibrations, plus wherever possible a thicker acoustic layer (foam or felt material).

Maybe some music lovers from the forum will have some experience to share?

 

I've dynomatted my whole car....floor all inner door panels, roof etc. When the door shuts, it's sounds even more solid. Acoustically, it's magnificent! Avoid the bitumen type sound absorbing mats, the closed cell foam type is now the way to go, foil Backed if possible for your initial layup, build in more deadening material around the back axle rear wheel wells and any large panels that resonate. You should be able to achieve Rolls Royce levels of silence.

 

I've done something similar as Sean B has done although I have used Dynamat Extreme as the base layer on all panels. Second Skin Luxury Liner Pro was added to areas which I considered to need additional insulation:

trunk floor
trunk inner wheel arches
rear seat inner wheel arches

To do this, I stripped the whole car down, as I was installing a top end hi-fi system and Parrot 9200 at the same time.

Like others have mentioned, the standard exhaust is really whisper quiet, unless it has lost some of its' baffle or is blowing slightly perhaps?

 

I also wanted to dampen out a little more noise from the rear of my 2005 XKR Coupe so I removed everything from the boot and lined it completely with aluminum backed sound dampening materials. When thumped, the spare tire well sounded just like a drum until it was lined. I then loosely "packed" open cell materials down along the rear seat margins where they meet the sides of the car. A db meter test before and after measurement resulted in a net nosie energy loss of 3.5-5 db. Be sure to line the tire well entirely and be sure to include the open cell materials packed along the seat margins.

 

Thanks to you three. Goldlion, can you please explain to me what is the open cell material you are refering to ? Is this a kind of felt or an open cell "plastic" foam ?

Rear seat margins : sorry for my limited english, can you also explain this to me please ? Have you done everything through the boot (sorry the trunk), or have you put some of these materials from inside ? Anyway, a 3 to 5 dB average attenuation seems really worth doing it !

Thanks again, this is really the kind of hands-on experience I was hoping to find from here.

 

Hello f-xo

I did the trunk first. I removed all of the trunk liner material and the spare tire. The liner sections "pop out" rather easily. I then vacuumed and cleaned all the metal surfaces prior to applying the aluminum backed dapening materials. It is a good 4-5 hour job of bending over into the trunk...a real backache. I aslo lined the area where the battery is situated. I used a product called "Damplifier Pro". If you use the same or similar product plan on wearing a tough pair of leather work gloves as the aluminum foil backing can be quite sharp.

For the back seat area I worked in the car carefully pushing strips/chuncks of sound dampening foam into the spaces where the back seats fit up to the sides and floor of the car. Without too much effort you can push the foam in by hand. Oh, I also emplaced a sheet of sound dampening foam under the rear speaker deck from the trunk of the car. This simple application really made a big change in the sound perfromance of the sub woofer.

I hope this information will be helpful.

 

To put a double layer into the entire trunk area will take at least 5 hrs work (nearer 10 for me) and it is back breaking work. Wouldn't want to do it for a living that's for sure! !!

Once its done, the rest of the vehicle is relatively straightforward, although access to the inner door panels was a bit limited. My car runs 20" detroits which do generate quite a bit of road noise. Doing the floor pan quietened things down a few notches.

You could also apply sludge, a sound deadening filler to the underside. Havent experience of it myself but the sound guys use it as well to keep noise out.

It will never be like a dentist's waiting room though !!!

 

Thanks guys for the tips. Once temperatures in my garage get back to reasonnable values, I'll think about getting to work. But for sure I don't want it to be like a dentist waiting room. No scream in my car, it would just scare me !

 

A while back someone mentioned a product that is similar to Dynomat but it's sold at home improvement stores. It's an aluminum insulation material that is sticky on one side. I've seen it before, but when I went looking for it I couldn't find it. Apparently it's a fraction of the price of Dynomat.