Noise absorption

MrBlobby · 17 May 2013 at 13:40

A while ago I found this really great product is was spray on noise absorption foam, more effective than dynamat and lighter. On the website they covered a battle ship with it. Anyway I thought I'd get some for my car, but I've lost the bookmark

Anyone have any idea ?? It was American website but they gave me a link to people who sell it in the UK

Tom_ed1987 · 17 May 2013 at 15:30

Dyanmat is a deadener, there are lots of liquid alternatives;

http://www.spraydead.com/

MrBlobby · 17 May 2013 at 18:59

Thanks is that the best stuff ?

I'm in the UK so what would you recommend

bitslice · 17 May 2013 at 22:19

MrBlobby said:
more effective than dynamat

Unlikely.

What problem are you trying to solve here?

MrBlobby · 17 May 2013 at 22:21

Nar it does exsist or did

I don't like noise

bitslice · 17 May 2013 at 22:55

MrBlobby said:
I don't like noise

Dynamat is the best solution.

There is the dumb way of doing this by adding mass which creates inertia in the panel, or the clever way using visco-elastic materials like dynamat which convert a greater amount of vibration into heat.

Spray on deadening is a bit pointless, adding material to the far corner of a panel which isn't vibrating, isn't going to do a lot. Equally it doesn't have enough mass to do anything useful.

A small patch of dynamat around the speaker housing and a second small patch on the outer skin is all that is required. Covering the whole door gets you rapidly into the law of diminishing returns.

Dogbreath · 18 May 2013 at 08:51

bitslice said:
Dynamat is the best solution.

There is the dumb way of doing this by adding mass which creates inertia in the panel, or the clever way using visco-elastic materials like dynamat which convert a greater amount of vibration into heat.

Dynamat isn't exactly a lightweight material!

Jonnycoupe · 18 May 2013 at 09:09

bitslice said:
Dynamat is the best solution.

There is the dumb way of doing this by adding mass which creates inertia in the panel, or the clever way using visco-elastic materials like dynamat which convert a greater amount of vibration into heat.

Spray on deadening is a bit pointless, adding material to the far corner of a panel which isn't vibrating, isn't going to do a lot. Equally it doesn't have enough mass to do anything useful.

A small patch of dynamat around the speaker housing and a second small patch on the outer skin is all that is required. Covering the whole door gets you rapidly into the law of diminishing returns.

And neither absorbs sound....

Dynamat is not a mass loaded layer, typical automotive stuff uses foams and vinyl loaded felt to decouple the panels and block sound. Dampeneds work from trying to stop panels generating noise in the first place but that does nothing for engine or tyre airborne noise.

bitslice · 18 May 2013 at 09:40

Dogbreath said:
Dynamat isn't exactly a lightweight material!

In a car weighing over a tonne, it's not particulary significant.

Jonnycoupe said:
And neither absorbs sound....

Dynamat is not a mass loaded layer, typical automotive stuff uses foams and vinyl loaded felt to decouple the panels and block sound. Dampeneds work from trying to stop panels generating noise in the first place but that does nothing for engine or tyre airborne noise.

Which is why I asked the OP what he was trying to achieve.
"I don't like noise" tells me naff all

so given that people only care about this kind of thing when they are listening to music, I gave him advice to improve that aspect. With hindsight I really should have just repeated the question until I got an answer - my bad.

If he's actually worried about tyre noise, changing tyres to a lower noise version wil help. The same advice stands, dynamat around the tyre wells will be most effective. Viscoelastic compounds are technically more efficient at low frequency suppression than MLV, that's not to say you can't combine them sucessfully, I just doubt the OP is willing to strip his car to do this.

Dampends work from trying to stop panels generating noise in the first place

How do you think vibration gets from the tyre to the cabin? By vibrating the panel in between, so you dampen that panel to reduce this effect, so I'm not sure why you think the product doesn't have the property of 'absorbing sound', when that is what it was engineered to do, convert vibration into heat.
Sound absorbtion foam is only going to influence sound once it is already inside the cabin space (which is why it is used in studios), so yes it going to have some effect, but it is harder to implement.

If you can find any unbiased opinion that a mass loaded spray is technically better than a viscoelastic compound, I'd be interested in their testing methods.

MrBlobby · 20 May 2013 at 22:55

This is the stuff http://www.acousticalsolutions.com/quietcoat looks like they've gone bust and the ship video isn't on there !

MrBlobby · 20 May 2013 at 22:58

Here's the video
http://www.youtube.com/watch?v=j2MC4oeEwiY

Jonnycoupe · 20 May 2013 at 23:24

bitslice said:
In a car weighing over a tonne, it's not particulary significant.

How do you think vibration gets from the tyre to the cabin? By vibrating the panel in between, so you dampen that panel to reduce this effect, so I'm not sure why you think the product doesn't have the property of 'absorbing sound', when that is what it was engineered to do, convert vibration into heat.
Sound absorbtion foam is only going to influence sound once it is already inside the cabin space (which is why it is used in studios), so yes it going to have some effect, but it is harder to implement.

If you can find any unbiased opinion that a mass loaded spray is technically better than a viscoelastic compound, I'd be interested in their testing methods.

The vibration is either structural borne from vibration travelling through bushes or airborne that travels through air, tyre roar tends to be high frequency and is why you want a foam to absorb the energy rather than mass layer. Mass layers simply changes the response of the panel such that it moves outside the operational envelope of the car and doesn't carry the sound to the other side of the panel by vibration. That's the structural borne sound, if its not resonating there is little vibration to convert to heat. Airborne is noise that already exists and a different approach is needed, that's all I was pointing out.

I've seen far too many cars coated in dynamat when a fraction would be just as effective and then there is nothing to actually absorb the sound.

bitslice · 21 May 2013 at 00:17

Jonnycoupe said:
tyre roar tends to be high frequency and is why you want a foam to absorb the energy rather than mass layer.

Agreed.
Although there are technical limitations to this.

Tyre noise peaks at 1000Hz
That's a wavelength of 34cm

For a porous absorber, the maximum particle velocities occur at 1/4 and 3/4 of the wavelength. If the thickness of the absorber is much less than one quarter of the wavelength, they will have little effect.

Therefore the acoustic foam has to be around 8.5cm thick.
Awkward

I've seen far too many cars coated in dynamat when a fraction would be just as effective and then there is nothing to actually absorb the sound.

Yup, I meant to come back to mention that dynamat is still effective when used to cover 25% of the panel, covering everything isn't necessary.

Looking at what vehicle manufacturers use, I've not seen anyone use actual acoustic foam? It's either jute, cotton wadding or recycled foam and at most around 1cm thick. Tyre liners appear to be mostly rubberised or fibre boards.

Actual testing is hard to track down, the web is full of before/after videos with nothing more than "OMG Awesome" as a conclusion :rolleyes:

or pointless tapping of something with a hammer.
So yes I can see acoustic foam would have some effect, I just couldn't comment on how best to implement it or what the outcome would be, especially given the lack of empirical data.

Clarkey · 21 May 2013 at 00:32

IME, regular old fashioned foam is the best at quietening things down. Got at least an inch thick of the stuff throughout the BMW. Remove it and things get massively noisier with the tar like stuff still on the panels. In fact, removing that stuff makes almost no perceivable difference once the carpet/foam is in.

Dogbreath · 21 May 2013 at 00:32

bitslice said:
Agreed.
Although there are technical limitations to this.

Tyre noise peaks at 1000Hz
That's a wavelength of 34cm

For a porous absorber, the maximum particle velocities occur at 1/4 and 3/4 of the wavelength. If the thickness of the absorber is much less than one quarter of the wavelength, they will have little effect.

Therefore the acoustic foam has to be around 8.5cm thick.

It needs to be that thick for maximum absorption, but absorptive materials are still effective down to about 1/10th wavelength.

bitslice · 21 May 2013 at 00:51

I didn't respond to this bit, sorry

Jonnycoupe said:
Mass layers simply changes the response of the panel such that it moves outside the operational envelope of the car and doesn't carry the sound to the other side of the panel by vibration.

In that they move the resonant frequency downwards.
Yes this is true for simple mass loading, but dynamat is a viscous-elastic material and so the dampening effect is over a much broader frequency range.
It's an important distinction when comparing the various methods.