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Old 12-09-2024, 09:49 PM
gtospieg gtospieg is offline
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Default dynamat or kilmat or siless max?

Curious if anyone has used the Siless Max. Kilmat and Dynamat are .08/.07 inches thick while the Siless Max is .12. Any pros or cons. I used Dynamat on the last car and that stuff is expensive. Is there really a difference between Dynamat and Kilmat? Obviously the Siless Max is thicker...so who has real world experience with the Siless Max? Thanks...

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Old 12-09-2024, 11:57 PM
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Dynamat, Kilmat, Siless...they are all constrain layers. They are designed to add mass and rigidity to the steel panels of the car, cutting down on sympathetic vibrations, hums etc. Since the floors in these cars aren't completely flat and have some structure to them, going with a very thick constrain layer may not be necessary. Where going to a thicker material would be helpful would be anywhere that you have a large flat surface, like the roof skin, door skins etc.

You don't need as much of the constrain layer as you think you might need. You certainly don't need 100% coverage like you see in pictures, unless you're really trying for rolls royce levels of refinement. You just need enough so that when you whack the panel it provides a dead thud without any sympathetic vibration.

Next, you want to look at is adding an acoustic underlayment on top of the constrain layer. This is your decoupling layer. It's what provides hot and cold insulation, dampens vibrations to the occupants and provides some acoustic absorptions. I use the Undercarpet Lite product from Boom Matt and have been happy with it. This is the stuff you can try for 100% coverage on. Think of it as the jute padding that is attached to the factory carpet.

For most people that want to tone things down a bit, but still have some of that muscle car rawness, this is where you would stop. Put your carpet of choice on top and you're good to roll.

If you want to go further into reducing sound and road noise, you start adding mass, typically via mass loaded vinyl. The more of this stuff you add, the quieter the car is going to get. Specifically target areas around where exhaust pipes and mufflers are, the inside of wheel wells, firewall etc. Basically anywhere that can be a source of freestanding audio waves that the car itself is creating. If you're going that far, doing a constrain layer like lizardskin directly on the doors and wheel wells also helps. This stuff is heavy though, so if you're after performance, it's a compromise you may have to think about.

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Old 12-10-2024, 12:09 AM
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OK so Garage Squad says go with the cheap stuff like Frost King or the like from Home Depot or Lowe's. I realize they are in and out in 2 weeks, but is there anything to that or is a waste of $$$$$?

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Old 12-10-2024, 12:11 AM
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Although Thermotec is known for its thermal products, I used their acoustic-damping material to totally line the cab of my '59 GMC. I'm very happy with it and it wasn't very expensive (12 years ago).

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Old 12-10-2024, 10:35 AM
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OK so Garage Squad says go with the cheap stuff like Frost King or the like from Home Depot or Lowe's. I realize they are in and out in 2 weeks, but is there anything to that or is a waste of $$$$$?
For the constrain layer, yeah it's just butyl rubber with a foil backing. You can literally use roofing material if you want. This isn't the area that I would spend most of the money. Based on what you want, I would have more money in the decoupling layer and mass layer if you are going that far.

That said, I did the dynamat custom cut stuff in my firebird and it saves a lot of time be being pre-cut for the application. Time is money, so sometime that type of deal works out in your favor, even if the actual cost is a bit higher.

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Old 12-10-2024, 01:11 PM
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For sound & heat control there is another option that lots of guys are using nowadays with excellent results... its a spray on product called lizard skin, its water based & very easy to apply, according to info & reviews it works as good or better than the different options mentioned above.

A friend that owns a hot rod & muscle car type body shop (no new stuff or insurance work) has been using it for man years with no complaints from him or customers and a friend doing a higher dollar rotisserie pro tour 73 firebird used on the underside, trunk and full interior metal. Seems like very good stuff and has almost zero resonance or vibration when slapping it with your hand or lightly with a hammer. Granted, its more permanent that the dynamat type stuff but is another option to consider.

https://lizardskin.com/

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Old 12-10-2024, 02:08 PM
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I'll be the odd man out here.
We utilized Kool Mat (https://www.koolmat.com/heat-resista...at-protection/) in our 66 GTO with the Mass Backed carpet.

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Old 12-10-2024, 05:01 PM
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Thanks for the responses. My question specifically is about "Siless Hybrid". Their ad claims that it is 3 layers(butyl mastic, PE foam, mass loaded butyl membrane) with sound deadening AND heat control. This stuff is a bit thicker than the other products mentioned( .2 inches vs .07 or .08)Has anyone had any first hand experience with Siless Hybrid. Thanks.

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Old 12-10-2024, 05:36 PM
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I haven't had any direct experience with that product, but based on it's thickness alone, it's not going to do all that it claims to.

If you tore apart the interior of a mercedes E class, you'd find about 3" of material between the floor board and occupants.

You can only put so much mass into certain amount of thicknesses, and absorption material for acoustics needs not only mass, but a medium to travel through. It's the same reason a 24" muffler will quiet exhaust better than a 14" muffler.

Even on their amazon page, they offer a spreadsheet showing the products you need for your desired outcome. The Siless Max is just the constrain layer. It's probably a fine product. I wouldn't be afraid to use it. The price seems pretty decent on it.



As you can see from their own information. You're still going to want a 2nd decoupling layer and possibly a third mass layer.

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Old 12-10-2024, 11:32 PM
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JLMounce...I read the same thing. That's why I'm curious about "Siless Hybrid". Obviously we can't put 3" of anything under our carpets in these old cars. I'm just looking for something a bit better than factory and thought that the Siless Hybrid might be a decent alternative. PS...just realized my original post referenced "Siless Max"...it should have been the "Siless Hybrid"...sorry for any confusion.

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Old 12-11-2024, 11:40 AM
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Oh gotcha, that makes some sense. I just looked into the product. The idea is good in theory, but my sound engineering education says that this isn't anywhere near thick enough to really do much on the acoustic side.

Is it going to be better than just the siless max or dynamat alone? Yes. How much better though is debatable.

The way that sound absorption works is by making frequency waves pass through a medium that reduces their amplitude. The density and thickness of that medium both play a role in how much amplitude reduction you see. It's also important to note that because sound waves bounce, you necessarily send those waves through that medium twice, so there's some squaring that occurs. The more absorption medium you have it gets better almost exponentially.

It's really going to come down to your goals. If I was building a race car that I drove on the street, I'd probably consider using this stuff as an all-in-one solution to make it somewhat bearable. I have concerns that this product would be able to deliver actual noise reduction and heat insulation with it's available thickness. You can even see that in the 4 stages that they tout, they are using the hybrid product with the other products, but never by itself.

If I was on a budget, I'd try the Amazon Basics sound deadoner
https://www.amazon.com/AmazonBasics-...1zcF9hdGY&th=1

And I'd do an underlayment on top of that. This is what I have in my bird.
https://www.amazon.com/Design-Engine...AUTOMATED&th=1

Then put your carpet on top. For the underlayment I found that the 72" by 70" was more than enough to do the cabin and trunk on my car.

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Old 12-11-2024, 06:18 PM
gtospieg gtospieg is offline
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JLMounce...Thanks for the additional info. I was thinking about the siless hybrid and carpet with the backing(would have to be better than dynamat and carpet with backing alone). Maybe siless hybrid and that "under carpet lite" with carpet and no backing would be a better alternative. Was there any problem fitting an extra 1/2" of mat under your carpet? Did you use a carpet with a backing or not(is the backing necessary)?

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Old 12-11-2024, 06:34 PM
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Originally Posted by gtospieg View Post
JLMounce...Thanks for the additional info. I was thinking about the siless hybrid and carpet with the backing(would have to be better than dynamat and carpet with backing alone). Maybe siless hybrid and that "under carpet lite" with carpet and no backing would be a better alternative. Was there any problem fitting an extra 1/2" of mat under your carpet? Did you use a carpet with a backing or not(is the backing necessary)?
For the most part, no it wasn't any more difficult. There's a little more trimming necessary of all the underlayment around the seat pedestals though.

The carpet I have does also have the jute backing under the driver and passenger feet as is typical with reproduction carpet.

So my total solution is dynamat, followed by Undercarpet Lite, followed by jute backed carpet. In the trunk I have dynamat and the undercarpet lite only. The nice thing about that undercarpet lite product is the synthetic material is moisture wicking, so if things do get a little wet, it doesn't rot or mildew.

If you're using a product like undercarpet lite, the added backing applied to most stock type carpets isn't going to hurt, but it's probably not incredibly necessary. That opens you up to using nicer carpets if that is your thing.

I would certainly like a mass loaded vinyl on top of the underlayment vs the jute backing. It's more weight, but would be around the same thickness and provide better acoustic control.

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Old 12-11-2024, 11:07 PM
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Thanks for the info guys, keep it coming! I'm about a year out but taking notes. Who knows where tech will go by then!?!

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Old 12-12-2024, 10:08 AM
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JLMounce...so it sounds like the jute backed carpet wouldn't be a necessity(save a few bucks on carpet) if using the Dynamat or Siless hybrid and Undercarpet Lite. What is your product of choice for the mass loaded vinyl?

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Old 12-12-2024, 10:41 AM
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JLMounce...so it sounds like the jute backed carpet wouldn't be a necessity(save a few bucks on carpet) if using the Dynamat or Siless hybrid and Undercarpet Lite. What is your product of choice for the mass loaded vinyl?
I haven't done anything with MLV since I care about weight and I wasn't looking to go too far in the noise department. So I don't have direct experience with anything.

However my research on the subject leads me to believe that the Second Skin Luxury Liner is a a pretty go to product.

https://www.secondskinaudio.com/soun...0aAlNlEALw_wcB

They do also make a Luxury Liner Pro which is a 2-1 decoupling layer and MLV layer combined. It's pretty spendy though.

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Old 12-12-2024, 04:49 PM
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JLMounce..thanks for the info on Second Skin. I just talked to Eric at "Second Skin". Probably about $600 to do the Luxury Liner Pro for the floors and "Mega Zorbe" for inside the doors. I would still need to do the sound deadening first..Dynamat or equivalent. If I don't have enough Dynamat left over they offer "Damplifier"(more $). So, yes, not inexpensive. But the wife wants this car to be quieter than the other one. Permission to spend more money?...Apparently this is the stuff Lexus uses.

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Old 12-12-2024, 05:00 PM
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Yes my understanding from my research is that second skin is industry grade stuff. With the MLV, it's a more is more approach. It's expensive and heavy, but the more you use, the better it works.

Tell the wife you'll make the car caddy quiet, but you'll need an engine with a bunch of torque to motivate all the weight it's going to add!

Since it sounds like luxury over performance is the goal, do yourself a favor and also shop an exhaust system that breathes well while being quiet. Generally speaking the larger packed mufflers are your best choice here. If you can get a 24" truck muffler under the car, that will help.

Tires also. Try and pick out tires with good road noise ratings. I don't know what size wheels you're after, but if you're doing anything in modern sizes, I really recommend the Nitto INVO. That tire rides very nice and has really low road noise creation.

While the sound insulation always helps, the less sound you're actually introducing to begin with, the better the outcome will be.

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Old 12-12-2024, 05:38 PM
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Already thought about mufflers, 20" instead of the 14" that come with Pypes systems, not sure 24" fits in a 67 GTO. Going to be using 15" wheels, at least initially, so may be limited in tire choices. Engine will be a 400 stroked to 434 so not worried about torque.

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Old 12-12-2024, 05:55 PM
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Sounds like it's going to be a really nice cruiser for the family!

If you can get a lot of this whole suite of materials on the firewall, doors, over the mufflers and around the wheel houses, that's where you're going to get a lot of mileage.

I'm not sure if the 67 GTO had a rear seat backing board or not. If it doesn't, try to make one from thick cardboard stock and put all this stuff on it. It'll make a huge difference with exhaust noise that travels from the tail-pipes, through the trunk and into the passenger cabin. Adding extra jute in the seat back also really helps as well.

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