Anyone use Dynamat, Second Skin, or whatever in their XJS?

 

Only used it in the trunk floor. Interior flooring did not bother with.

 

I used a similar product to replace all the old sound deadening. I also put a pad on the roof under the headliner.

 

Was it worth the effort and cost?

 

Looks good. Do you think it was worth the cost and effort?

 

Why the trunk?

 

I had the car in bits already for a bare metal respray so the effort to install the insulation was minimal at the time. I did this 5 years ago and I can not remember what it cost, would I do it again - yes definitely. The only other deadening I have is an underlay under the floor mats which is removable. Made from closed cell foam with a butyl centre.

Much lighter than the old Jaguar sound deadening and the heat transfer in the footwell is also a lot lower, the drivers footwell now stays quite cool in our hot weather.

 

I tried the Dynamat-type stuff in my VW Passat, and it didn't work very well. The problem is that the dense layer is not spaced away from the substrate.

The physics of soundproofing is such that a dense =layer, which is what the dynamat is, really works best if it is spaced off the floor/bulkhead with sound absorbing material. The sound then reflects back and forth between the metal, and the absorbent layer, and gets turned to heat. Take a look at best OEM stuff, that's how it works - a foam layer, with a dense (often bitumen on older cars) layer on top.

You can buy the equivalent from Soundown. Their composite insulation has a heavy, lead-loaded PVC layer, spaced with sound-absorbing foam. I used it to soundproof a horribly noisy diesel on my boat, and it works really well. If I was doing a car again, that's what I would use.

https://www.jamestowndistributors.co...eText=soundown

 

Because the trunk (boot) is a big resonating box which amplifies sound. I had an Opel once that was really noisy and I bought a soundproofing kit for it. I tested it at each stage as I fitted the kit: engine bay, interior and boot last of all. It was the boot that really made the difference!

 

A lot of road noise is under 1KHz and this requires a very large gap and/or thick dense sound insulation more than 25mm

The sound deader fixed to the metal provides constrained layer damping, the metal the butyl and aluminium have different resonant frequencies. When bonded together if the resonant frequencies are far apart this gives a large Q factor damping any frequency vibration between the bell curve coming through the car body. It does work, tap on a panel in my car and there is a dull thud, no ringing as it did before I installed the Sound Deadener, I have calibrated sound measurement equipment and I did before and after measurement tapping the floorpan with a number of different

I said Butyl but its actually mass loaded vinyl underlay which provides further sound deadening. This is the stuff they use in new high end cars.

 

Dynamat works well as a dampener. For sound absorption, you also need something like closed cell foam over the Mat. Lizard Skin sells a three-part product which reportedly works well. The issue is sound deadening vs. dampening vs. absorption. Lots of videos on YouTube explaining the difference. The problem (for me) is that all the products are pretty pricey and I'm not sure if it's a good ROI.

 

I wonder what happens if you put closed-cell foam between the mat and the metal.

I used this mat which appears to be as good as Dynamat at a fraction of the price :


Also, Foam Factory sells closed-cell neoprene foam at a reasonable price. Finding alternative sources to the boutique car products is the key to keeping costs down.

My suggestion would be some combination of the above (would be interesting to hear thoughts on having the mat over the foam vs. foam over the mat) plus a mass-loaded vinyl sandwiched layer in key places. This latter stuff is expensive but worth the money.

Also interesting to hear any thoughts on what those key places would be.

 

The Dynamat type of material is more of a sound changer than a silencer. It alters the sound made when you tap on sheet metal into a nice solid sounding thud.

Mass loaded materials will absorb or reflect sound.

 

Sound and room treatment is one of my hobbies I am setup with calibrated acoustic measurement equipment and I have setup quite a few listening rooms. Measure and treat the room to improve the sound, so used what I know to also treat my car to reduce the noise inside.

For sound insulation there are 2 different methods required, high frequency and low frequency.

It is possible to reflect higher frequencies and these are easy to deal with. Only hard surfaces will reflect sound, MLV absorbs the sound by turning into heat.

The thin MLV (Mass Loaded Vinyl) works well for frequencies above 1KHz, but a lot of road noise is below 1KHz, at 60Hz the MLV does not exist the low frequencies will pass straight through. Like the DUF DUF you hear from some cars the low frequencies are passing un-attenuated through the car but the high frequencies are bouncing around inside.

Low frequencies do not reflect much and require mass and/or thickness 100mm at a minimum to attenuate below 500Hz. This is where the CLD is somewhat effective, but still above 100Hz. There is no way you can put 100mm of sound insulation in a car unless it is a newer Bently which use very thick floor insulation spaced off the lower floorpan, very effective.

I have something like this under the carpet mats. It has foam top and bottom with MLV sandwiched in the middle and is quite heavy. This and the Dynamat do work well and will about the best you will get within the constrains of the vehicle.

https://www.ebay.com.au/itm/Dodo-Sou...-/161604531510

 

To "deaden" unwanted noise, you place material over metal to reduce vibrations which in turn reduce unwanted car noise. Any time you read the term "Sound Absorption", it's referring to the process of stoping metal from rattling and it's usually when someone is explaining how to soundproof a car.

 

To "deaden" unwanted noise, you place material over metal to reduce vibrations which in turn reduce unwanted car noise. Any time you read the term "Sound Absorption", it's referring to the process of stoping metal from rattling and it's usually when someone is explaining how to soundproof a car.

 

Admin,

Do the above 2 posts on a thread from 4 years ago seem like they are coming from a genuine new member?

Paul

 

Visit Resonix.com if you really want to know how to properly sound deaden and block outside noise. Tons of info and Nick, the owner, has extensive videos to explain and help understand the products and process.