23 replies to this topic

[BIGW]

It may look like its sealing the large gaps but there's no way its stopping significant amounts of noise from travelling through. Noise will find the path of least resistance, mdf or air?

To stop vibrations, yeah it can work as an isolator to a degree. What is the intended purpose? To stop panel resonance or to seal around your wall?

[Captn_Awesome]

D34M0N.inc, on 14 March 2012 - 04:13 PM, said:

I use it in the skeleton of my boot lids to reduce rattles.

Id be careful doing that. The pressed frame of your boot is only tack welded to the skin generally and I've seen plenty of boots deformed from this stuff over expanding - especially in the heat.

Edit: BigW I can't believe your getting your arse around in a prado!

Edited by ~Sparkles~, 15 March 2012 - 09:41 AM.

[Lunchbox.inc]

BIGW, on 15 March 2012 - 08:48 AM, said:

It may look like its sealing the large gaps but there's no way its stopping significant amounts of noise from travelling through. Noise will find the path of least resistance, mdf or air?

To stop vibrations, yeah it can work as an isolator to a degree. What is the intended purpose? To stop panel resonance or to seal around your wall?

i think the best experience would be to use the stuff, as above, it doesn't do AS good as job as fiberglass, or something more solid, at completely isolating behind the enclosure, BUT if you were to use it, you'd understand exactly wht it DOES do, and it's alot,

even if you fiberglas all the box to the exterior panels, you only have a very small contact patch, vibrations, flex are still transmitted the entirely length off the roof and other panels, this equals a tone of lost energy still, you may have isolated the rear wave inside the cabin, but your still seeing significant energy losses...

where as if you just used expandy foam, you may not isolate that rear wave quite as well, BUT with tht much deflection of the sound/pressure trying to manipulate it's way around the tiny air pockets in the expandy foam, the rear wave becomes all but useless, not carrying anywhere near enough velocity to impact the front wave severely... not only that, but the use of expandy foam mas a MUCH larger contact patch,(usually the entire length of the enclosure) the dampens (severely) all the vibrations and flex you would have otherwise seen across the entire length of the roof...

this results in significantly less energy lost from flexing panels, as well as isolating the rear wave, a mix of both expandy foam and fiberglass or something similar, would be the perfect mix, and is quite a common one, BUT expandy foam by itself, is better than just fiberglass on it's own (if used just to create the seal)...

[D34M0N.inc]

Yeh i know this sparkles i roughly put 1 third in the area as it becomes 3 times it's size, I read up about it the first time i did it and read the proper way of doing it so that don't happen, worked every time sofar at decreasing rattles in my boot by 90%. Also the EF's only used a type of orange foamy sealer that viabrates out if the cars never had a sub in the boot before. So pretty much the skeleton part is free to slap on the boot lids underneath. So i re seal it with no more gaps after a bit of expanding foam and no issues with warping or rattles.

With the using it with the whole walling thing. Expanding foam is better than nothing in the long run, and is rather resistant to the viabrations to.

[BIGW]

Lunchbox.inc, on 15 March 2012 - 11:48 AM, said:

i think the best experience would be to use the stuff, as above, it doesn't do AS good as job as fiberglass, or something more solid, at completely isolating behind the enclosure, BUT if you were to use it, you'd understand exactly wht it DOES do, and it's alot,

I should clarify, I wasn't referring to isolating the enclose from the vehicle, that's a whole other topic, I'm talking about using it to seal around your wall.
Last year (2011) I spent close to $1.0m on acoustic testing at RMIT. Not ONE transmission loss test used expandable foam to seal around the aperture of the test rig. These expensive tests are designed to achieve the best result we can. I can guarantee expandable foam will never be used. I'm not telling you how to suck eggs, more so giving YOU some real world experience with some testing in conjunction with simply put, the best acoustic consultants in the country with a slightly higher budget than building a car stereo.

If you have seen what level of mass and airspace is required to reduce significant amounts of energy at the frequencies you burp at you will understand that your rear wave will simply pass through the expandable foam.

And yes, I have built a wall before.

Kirk, I'm not actually rolling around in it yet, ordered in Jan, now they're telling me May delivery! Yes, before you say it, I'm getting old.

[Lunchbox.inc]

i can appreciate your tests, but if you refuse to trial expando foam based entirely upon theory (not practical use) and therefore have zero actual results on the products, then i can't see how those tests are of any relevance in this situation? an expensive test rig in ideal situations is barely "real world experience" but it better for getting measurable results...

i have no doubt that are better materials out there for the job, but the none of them are as user friendly as the simple old can of expando foam... as it allows you to build your wall, and then fill in any gaps later, as well as bracing the roof to an extent....

if you re-read thru my above post you'll notice i also pointed out that it is very common to use the expando foam to as a base to lay fiberglass over, so as to create a more solid seal, and i never stated that it was the be all and end all of acoustic treatments...

in all fairness however, what would you suggest as an alternative to help seal the rear wave...?

[BIGW]

Lunchbox.inc, on 19 March 2012 - 02:00 PM, said:

i can appreciate your tests, but if you refuse to trial expando foam based entirely upon theory (not practical use) and therefore have zero actual results on the products, then i can't see how those tests are of any relevance in this situation? an expensive test rig in ideal situations is barely "real world experience" but it better for getting measurable results...

in all fairness however, what would you suggest as an alternative to help seal the rear wave...?

It's not so much that I refuse to trial expando foam more so that I choose to take advice from a professor of acoustics with more experience in the field that I have been on this earth for.

For sealing around your wall, use something with dense mass to it multiple layers of cement sheet etc. For fine sealing around timber use a mastic sealant, or fire rated sealant they have excellenct properties.

[Lunchbox.inc]

BIGW, on 19 March 2012 - 02:48 PM, said:

For sealing around your wall, use something with dense mass to it multiple layers of cement sheet etc. For fine sealing around timber use a mastic sealant, or fire rated sealant they have excellenct properties.

i'll be the 1st to post that multiple layers of cement sheeting isn't exactly the easiest item to use in side a car, even less so trying to squeeze it between the roof and the enclosure... mastic sealant is a good one, but again, not exactly easy to use, you would need several gallons of the stuff just to seal the roof of most walls to the roof of the car... which still leaves expando foam as the most readily available, simplest to use product around, 2-3 large cans will usually seal up 90% of the wall, and then if any additional sealing is needed, you can simply glass over the top...

i'll also add that not all expando foam is made equal, altho not so commonly used, you can still get this stuff, and it'll do quite a sufficient job at sealing...

http://www.uscomposites.com/foam.html

16lb density expando foam...

[D34M0N.inc]

Expanding foam could be used then a layer of that mastic sealant over the top, then fiberglass over the top of that for prettyness and extra strength possibly. I would like to see a comparison of price to sealing ratio's (i guess you can put it that way lol)