Sound Deadening

[JW240]

I know this is a big topic, but like a lot I'm pretty nervous about adding new sound deadening after spending ages removing the original and repairing the results of its failure. Therefore I have decided to leave the floor pans bare for my own piece of mind, however I do need something as its so loud and boomy inside the cabin. Seems to be worse around the rear.
I was therefore thinking dynamt the tunnel, insides of doors, firewall, rear wheel tubs, boot floor and insides of quarter panels. Never used sound deadening or anything before, seems self explanatory though, just don't want to encourage the dreaded rust to start forming.

 

[Rob Gaskin]

Just search the Forum for 'Sound Deadening' it brings up 172 posts.

 

[Mr Tenno]

Worth bearing in mind, there's nothing intrinsically wrong with the original sound deadening (apart from it being under the paint rather than over).

As Rob says, there are some good threads on this already - you can even buy the original material from Nissan and cut it to the correct shapes.

 

[JW240]

Worth bearing in mind, there's nothing intrinsically wrong with the original sound deadening (apart from it being under the paint rather than over).

As Rob says, there are some good threads on this already - you can even buy the original material from Nissan and cut it to the correct shapes.

I did have a look through that thread, seems interesting. I was just wondering with modern technology if the material had come on somewhat and dynamat might be more efficient. Literally no idea.
Did come across the newer Dynapad which seems very expensive and I'm not sure how much it would add to the dynamat. Just like the idea as you don't have to stick it to everything.

 

[Mr Tenno]

Not sure myself, I tried to install Dynamat in mine and just found it a big sticky PITA.

The shiny foil also looks a little out of place once it's in.

 

[toopy]

I know this is a big topic, but like a lot I'm pretty nervous about adding new sound deadening after spending ages removing the original and repairing the results of its failure.

Not so much it's failure, more the lack of any real rust proofing and poor quality steel.

If your heater matrix or one of the hoses leaks unnoticed in to a foot well, sound deadening or not, permanently damp carpet is the real perpetrator here, that and holes breaking through from outside.

 

[AliK]

The MLV stuff adds mass and reduces the vibration / resonance of panels.

The closed cell foam, stops the sound bouncing about in the car. For example, you could always put down 1” thick closed cell foam under the rear deck carpet to reduce some of the bouncing about stuff and some of the boom. It’s a bit like the effect furniture has on an empty room.

However, it’s practically impossible to block out the low bass / booming frequencies as they travel through stuff. Have you noticed how the subwoofer of the car 3 in front of you at the lights makes your car shake?

This is a good illustration of the sources:



I found that insulating the insides of my door cards with 3 mm closed cell foam reduced a huge lot of wind noise on the motorway.


Insulating the strut towers with Silent Coat MLV massively reduced a lot of road roar from the rear.

the deck area and the spare wheel well act like a giant resonance chamber, so sparsely spread MLV and 25mm closed cell foam had a big effect in reducing some unwanted exhaust noise.

I went over the trans tunnel with MLV and 3mm closed cell foam over the top which reduced a lot of noise and heat transfer. The latter was really quite noticeable!

And so on. if you want to get rid of wind roar, you need to MLV the roof skin below the headlining - I haven’t done this but people who have say it has a dramatic effect.

So in short, yes you can eliminate some of the unwanted noise with just foam but you need both to get the full effects. Your foam by itself won’t stop the panels resonating and amplifying the vibrations / noises.

 

[AliK]

Ps. I found that in my garage with everything bouncing off the walls (and a cold engine on the chicle at 2k-2.5k rpm), I had a dB level inside the car of 101 before and 90-93osh after installing the sound deadening. When you wind the windows down you now notice a significant difference!! So it’s worth it if you want to spend a lot of time inside your car.

The only real way to get rid of exhaust boom is to install a centre resonator of the correct size.

 

[TimFZ]

Interesting thread, considering I am a low frequency noise consultant!

Traditionally, open cell foam is used for absorption but due to small space requirements, automotive industry often used closed cell foam as it can be thinner and works at a slightly lower frequency.

It's the dynomat damping (bitumen or similar) which adds mass and damping to the panels. This prevents drumming resonance on panels and causes the booming. Without lots of R&D time, add it to about 80% of the panel surface area for good effect. Car companies spend a lot of time working out where to put the minimum material to do the job to save cost and weight when many are made. You can just plaster it on...

Large area flat ish panels are the priority, then those with a single curvature, smaller and double curvature panels won't drum in the same way, you could use the closed cell foam.

Dont forget the roof panel, it's large and not very curved. Damp that and fit closed cell foam behind the headlining fir best effect. Floor panels benefit from damping but paint them first to make them water proof. (and as stated, check the floor regularly for damp!)

 

[TimFZ]

Re exhaust boom, agreed, resonator should help in centre section, as does a baffled main silencer but these often get rid of the character. Ideally for me, there is little boom but the exhaust comes alive at higher revs and throttle positions!

 

[Robotsan]

Started adding dodo mat hex to the floors. Not sure if I need to add it up the sides and cover more than I have already or not? Dodomat themselves say aim for a minimum of 50% coverage of a panel.. so surely I've done that for this section of floor?

Saying that, I will probably add a bit more to the sides of the trans tunnel where the old stuff finishes..

 

[TimFZ]

Car manufacturers go to great lengths to minimise material use and weight so often you find simple panels less than 20% coverage in doors etc.

However, having used this type of damping industrially, we used to aim for 70% coverage on a panel, and focus more on the flat sections than large curves like the trains tunnel. The degree of difficulty fitting to complex curves is outweighed by the law of diminishing returns so you are unlikely to notice any further benefit!

(just read that I put similar above previously! Sorry)

 

[Robotsan]

Car manufacturers go to great lengths to minimise material use and weight so often you find simple panels less than 20% coverage in doors etc.

However, having used this type of damping industrially, we used to aim for 70% coverage on a panel, and focus more on the flat sections than large curves like the trains tunnel. The degree of difficulty fitting to complex curves is outweighed by the law of diminishing returns so you are unlikely to notice any further benefit!

(just read that I put similar above previously! Sorry)

Haha don't worry, good to get confirmation! I hadn't read the bit about curved sections properly as it turns out. OK cool so I'll probably just do the main flat portions of the floor then. And then the roof.

Thanks!

 

[TimFZ]

The curved sections are intrinsically stiffer so less boom or low frequency control required. The edge damping around these stiffer sections can easily control the higher frequencies a stiffer panel produces. Hence the need for less damping.