215 replies to this topic

[3sum]

Just quickly, before I go out and buy any.

I am in the process of SDing my car and I was wondering if there is any point in applying any sound absorbing material, like that stuff shaped like an egg carton, to the outer skin? Especially behind the mid.

EDIT: don't worry. I just saw how much it costs

Edited by 3sum, 27 June 2010 - 10:59 AM.

[MADXF]

I've got a question that hasnt come up in here yet.
Is MLV absorptive, or reflective?
I'm wondering about possible issues with reflecting back-waves if the MLV was applied to the outer door skin.
If reflective, it would be better to attach it to the inner skin to block both speaker back-waves and external noise.
If it's absorptive, then there's no problem.

The next question I have is regarding this Jaycar product (http://jaycar.com.au...w.asp?ID=AX3680)
It weighs in at 4kg/m, nearly double that of Dynamat extreme (2.2kg/m).
From reading this thread, Dynamat's primary purpose is to add mass to a panel to reduce resonance.
If it is only for adding mass, then wouldn't the Jaycar product be better as it weighs more per square metre, and it is reducing external noise transmission?

Edited by MADXF, 08 September 2010 - 02:31 PM.

[~thematt~]

Absorb, not reflect, yes.

Heavier is better yes. But with heavier comes the need to stick to the surface better over time, given the conditions. My experience is, jaycar cant do that.

[MADXF]

~thematt~, on 07 September 2010 - 09:57 PM, said:

Absorb, not reflect, yes.

Heavier is better yes. But with heavier comes the need to stick to the surface better over time, given the conditions. My experience is, jaycar cant do that.

The item referred above does not come with a self adhesive backing so 'sticking over time' would come down to the quality of glue purchased.

I've got another question now...
I know that MLV is most effective when used with a CCF isolating layer, but how much is it's effectiveness reduced by not having CCF?

[~thematt~]

Hmmm, must have been different to the stuff I saw, because that stuff has an adhesive backing. If you have to glue it yourself, I'd say go for it. Much more effective, if its a butyl substrate, and not an asphalt.

CCF is critical to the performance. It isolates the layer from any sympathetic vibrations. MLV is pretty much useless without isolation.

[br85]

~thematt~, on 09 September 2010 - 10:23 PM, said:

Hmmm, must have been different to the stuff I saw, because that stuff has an adhesive backing. If you have to glue it yourself, I'd say go for it. Much more effective, if its a butyl substrate, and not an asphalt.

CCF is critical to the performance. It isolates the layer from any sympathetic vibrations. MLV is pretty much useless without isolation.

Not as critical as you'd think. A 1/4" thick layer of ccf doesn't provice NEARLY enough isolation for low frequencies. Basically MLV in cars just improves the Sound transmission loss already in effect by the sheet metal. Normal sheet metal has about 8db of transmission loss, coated in MLV it's got about 23-25db of loss. You pretty much can't get enough practical isolation using ccf to gain the "double wall" effect you're after. A guy on diyma has done some tests, and there's bugger all measurable difference with and without ccf. I've used MLV with contact advesive and 1kg of sikaflex (for edges) per door in a WB ute's doors and it made a HELL of a difference. I also used the 25% coverage rule with dynamat as well (mostly because it has no intrusion bars). Quietest 1970s V8 I've ever heard. I just used nominal dynamat with neoprene foam on the floors, pillars and roof. A little bit of knowledge and time sure beats throwing endless dollars at a problem. Not all people have the luxury of deadening a car with ZERO trim panels, carpets, or seats in, though.

[flinchy]

so should deaden the inner skin and the trims, which makes sense... what about the outer skin, i'm guessing that's a lot of extra effort for not much gain?

ED: ok, so searching the thread says 25-50% of it should be good... or use a closed cell foam? where can i get that, and what is it, and how is it different to something like dynamat? if it's better than dynamat (and presumably cheaper as it's been recommended with sound deadener being expensive), why not use it entirely in place of the dynamat/roadkill stufF?

Edited by flinchy, 01 September 2011 - 09:32 PM.

[shizzle]

Dynamat adds mass to panel and reduces resonance (vibrating panels)
MLV actually reduces the trasnmission of sound.

The two can be used in conjunction (dynamat on the panel and MLV covering the surface on top) for good effective, however, they both do different things, so not really a substitute for each other.

CCF is used to isolate the MLV from the panel, but as br85 points out, it is not that effective.
There is no one answer either to quiten a car, as they are all different, so each problem has to be looked at individually, and engineered out.
However, 25-50% dynamat or similar coverage over the LARGE unbraced panels in a car (roof, door skins, boot lid, back shelf) is a good start. Then a layer of MLV over the enitre surface (yes, you need to cover everywhere, as holes in the layer allows the transmission of sound) will stop much of the road noise.

You can then start using things like silicon, clay, foam, bracing etc to take it that step further, as the situation requires.

The above method will be cheaper in the long run, and more effective than throwing layers of dynamat or similar all over ones car.

GL

[pillowpants]

i use for sale signs covered with sound deadener to cover the service holes. They are rock hard.

Edited by pillowpants, 10 September 2011 - 04:02 PM.

[::: cal :::]

while on the topic of sound deadening, im after a bit of deadening for my boot and doors, but dont really want to compromise too much weight, is this superlight dynamat worth using?

[SleeperSaab]

::: cal :::, on 11 September 2011 - 07:41 PM, said:

while on the topic of sound deadening, im after a bit of deadening for my boot and doors, but dont really want to compromise too much weight, is this superlight dynamat worth using?

Cal, being realistic, adding dynamat to your boot and doors will add about as much weight as if you ate a full pizza then went for a drive. Even if you put a full box of dynamat into the car (i think that's about 10 sheets...) from memory, that's about 9 kilos. Or, about the same amount as a high schooler's back pack, a cricket bag or a couple of months of consuming too many beers and kebabs.

Have a look at other items in your car and work out the relative weights. Eg, a car seat might be 3 boxes of dynamat. Then work out the total weight of your car and the percentage change of adding a couple of sheets of dynamat. Eg, if one sheet is 1 kilo and your car weighs 1000 kilos, that's 0.1%

Once you've done that, look at whether you want a race track based car or a street car. If you want a race car, why do you have a stereo in it, or why is road noise an issue?

Not dissing you, but all people who look at weight being a factor in sound deadening need to put it in perspective.

And that's not even talking about the ratio of weight increase to sound quality/noise reduction.

[TRD]

guys

with regards to road noise from tyres do you find that you need fill gaps between panels etc with actual pieces of foam?

my supra has a heap of dynmat installed and it has certainly helped but my car also runs a 4" titanium exhaust as well 315 rear tyres. when traveling along the highway etc the road noise is pretty bad due to the stupidly wide wheels+tyre combo.

I realise a supra is never going to be great for sound deadening with the large rear window and hatch design howvere id really like to reduce the tyre huming while on longer drives.

I have a feeling most of the noise is bouncing through the exterior brake duct vent behind the door then resinating throught the cabin.

Im also looking at buying a couple rolls of dynapad for the back of the car. has anyone had any issues with the car smelling like rubber with dynamat installed.

any help would be great!

[Daedalus]

where are you guys buying the sound deadening material? i read some people bought from Jaycar. What about the branded ones? i would like to avoid the Supercheapauto paint if possible

what do you guys think of this cheap sound deadening material?
http://www.ebay.com....a#ht_3284wt_989

Edited by Daedalus, 03 January 2012 - 10:11 PM.

[TMM]

Amazon.com wasn't too bad the last time i looked. About $130 + $40 shipping for a dynamat bulk pack. Probably gone up since then though.

Regarding what is better, all deadeners do the exact same thing - turn kinetic energy (movement) into heat. Dense materials like dynamat are good at deadening low frequencies (and direct high frequencies such as the ringing from the sheet metal which they are attached to), and less dense materials (like foam) are better at deadening high frequencies. Foam CAN block low frequencies effectively but it has to be thick - like half a foot thick, and high density. That makes it impractical for installation in a car, and hence why we use thinner higher density products like dynamat.

There is no point in putting a thin foam 'deadener' underneath your carpet, seats or door trims because the carpet/seats/trims will already block the high frequencies, and a thin foam will do jack to the low frequencies. It might do *something* but it's unlikely to make a measurable difference.
Foam however is good at preventing parts rattling against each other, so you can use small pieces to prevent interior trim rattling.
Products like Dynaliner are best used as thermal insulation rather than as a sound deadener.

If you have tyre noise or exhaust noise and you have already installed a heavy deadener like dynamat, well there isn't much you can do except for getting a quieter exhaust/tyres.

The other property of acoustic materials is reflection. Thats where those corrugated foam acoustic tiles come into action - they turn a harsh directional reflection into a soft dispersed reflection. Again they have to be THICK to work. The only place i can think of where these would be useful in a car is behind door mounted speakers (but then you have to deal with foam getting wet) or if you don't mind the interior of your car looking like a recording studio.

Edited by TMM, 28 January 2012 - 01:23 AM.

[Aussierox]

Marc ♫, on 31 March 2005 - 02:14 PM, said:

Discussion from Technical Article

Is it just me or does the link to the technical article not work?