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 Post subject: Sound Damping Materials?
PostPosted: January 7, 2019, 4:59 pm 
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Joined: January 14, 2006, 1:06 pm
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Location: Vista (north of San Diego CA)
Anyone have experience with sound insulation? Recommendations? Any unique approaches?

It seems that a lot of the sound damping stuff out there is dealing more with heat than sound. And it's hard to tell from product descriptions how effective it is. They all are the "maximum" and "ultimate" but no one gives real world examples with sound level decreases.


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PostPosted: January 7, 2019, 5:37 pm 
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Joined: December 24, 2007, 5:11 am
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Location: Seattle area
Hey John,

Built my car in a friends auto stereo shop (he had a lot of tools and he could weld) and they sold a lot of a product called Dynamat. Not cheap, kind of heavy but thin and would really cut down on sound getting out of the car. You know how those big woofer guys are. Some would come in with their license plate rattling like crazy. He would instal some Dynamat and viola, fixed.

Good luck

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PostPosted: January 7, 2019, 6:53 pm 
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Big topic but it boils down to what kind of sound transmission you are trying to affect. Excitations shaking parts that become speakers or sound generated by a noisy thing (engine) moving to the driver's ear. BTW, I'm not an N&V engineer but I sit in close proximity to a few here at GM and have soaked up as much as I can.

I think on a car like this it's the first one. You really want to move the resonant frequencies of the panels away from typical frequencies generated by the engine or road inputs. A product like dynamat is really designed as an easy way to add mass (and some damping) to a panel which lowers it's resonant frequency, it's not great at actually stopping most sounds from moving through it (although better than 0.040" aluminum for sure). It also wasn't really originally designed to be applied like most hot rodders do, completely covering every possible surface. The idea would be to pick a large aluminum panel and put just a small square of dynamat or similar material in the center. You can imagine how that would change the ring or buzz of that panel to a thud. There aren't too many road or engine inputs on a locost style car that will excite a panel that "thuds" but there are tons that excite panels that "ring" or "buzz." You can play with how big a square you need on each part but it won't need to cover the majority of any one panel by any means.

BTW, there's a 6" wide rubber roofing tape available at HD or Lowes that is very nearly the same as dynamat and 100 times cheaper. I've used both and while the real thing is a bit more flexible and with a bit better adhesive the results are the same (as physics says they should be, damped mass is what you care about, not some crazy material property).

The other thing that the sea of dynamat that you see in most hot rods does is a secondary or accidental function of covering gaps. Sound, especially high frequency, will find it's way through surprisingly small gaps and if you are sticking that stuff everywhere you're bound to cover some up. You can do this with whatever you want, doesn't have to be dynamat. It would be cheaper and just as effective to use $20 bills to fill any gaps, actually. (can you tell I'm irritated by the cost of that stuff?)

On the other end of the spectrum, if you have a noisy "thing" like an engine and you want to take that noise out of the cabin you can use an absorptive material. Most common for the aftermarket community is 'jute', that material that looks like shredded old t-shirts stuck to a foil backing. There are many other kinds too but you get the point, it absorbs the sound, totally different mechanism than dynamat (and dynamat is actually really bad at absorbing sound).

In my opinion there's not much use to absorbing sound on these cars, the airborne path from the engine, diff, etc, to the driver's ear is pretty much a straight shot so blocking it at the footbox or firewall or soaking it up with jute is not going to help much. However, the need for mass damping of panels is huge and that's where I would focus my efforts using the Home Depot roofing tape (or dynamat if you're rich).

Alex


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PostPosted: January 7, 2019, 10:56 pm 
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Joined: September 30, 2005, 1:28 am
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Location: Sunny-Okanagan, Canada, eh?!
My Locost is 119dB of wind noise at 90km/h. I don't think you're going to notice much in the way of sound deadening.

I do, however, recommend building with a sense of "how can I secure this so it doesn't rattle?"

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PostPosted: January 8, 2019, 12:52 am 
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Location: Carlsbad, California, USA
Hi John,

There are examples of how to apply the sound deadening materials on vendor websites and YouTube. As was mentioned by ajmacdon above, you don't have to cover the entire surface to have an significant effect. The better application videos get into that.

Long story short, I put quite a bit of time researching what was available, and especially looking for affordable materials. For sound deadening I found the following product on Amazon and it is a fraction of the cost of DynaMat and similar products:

Noico adhesive butyl/foil deadener ==> https://www.amazon.com/gp/product/B00UR ... UTF8&psc=1

It's made in Russia and is of very good quality. It is quite heavy, as they all are. I have a box here in the garage if you want to come over and see it. There is also a decent video for the product on the Amazon product page.

The other two potential issues are heat transfer from the power train and road, and high heat from the exhaust. I'm using a foil-backed, artificial "jute" material on the inside of the trans tunnel and some parts of the engine compartment. It is light compared the buytl panels and keeps heat out and has some sound deadening properties too. You can see applications of it in my build log. I bought it through an outfit in Bakersfield. It's a very effective and safe material, and pretty inexpensive relative to many other products. I have some samples of that you can look at. You put it on with a spray adhesive.

Neither the butyl panels, nor the foil-backed jute can be used close to high heat sources. I have that situation at the footwells, where the exhaust headers run very close to both of them, and bought what's called 'zero clearance' heat shielding. It can be placed very close to the exhaust, and almost touch it. I found a company in North Carolina that supplies NASCAR teams with one of the most effective, yet (relatively) inexpensive products. I haven't even opened the box yet, because I'm a ways off from applying it. We can open it and look at that too if you like.

Those last two applications may not interest you. However, I wanted a comfortable cruiser, so I don't want hot spots like a lot of Locosts have where you fry your feet or elbows after you've been on the road for a while. I can dig out info on the last 2 product and companies if they interest you.

Cheers,

Lonnie

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PostPosted: January 8, 2019, 9:08 am 
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Joined: January 31, 2012, 12:49 pm
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Location: Louisville KY
I'd think that the position / angle of the exhaust tip would probably be worth looking at as well? Oh, yeah, and those mufflers....

The wind noise would have to be another issue, and that's been a topic of conversation here. Basically the front windscreen and the fronts of the rear fenders make lots of wind noise, but short of installing one of Jack's Lalo kits I don't know how to do anything about that. Oh, people have tried, but I don't know that it did any good?

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PostPosted: January 8, 2019, 9:40 am 
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Joined: July 17, 2008, 9:11 am
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With tire and wind noise alone measured by many builders (myself included) running 90-119dB, any sound deadening insulation will only be adding weight IMO. Now for temperature insulation...…

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PostPosted: January 8, 2019, 5:06 pm 
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Joined: January 14, 2006, 1:06 pm
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Location: Vista (north of San Diego CA)
Thank you all for tons of excellent information. Great points about damping, coverage and low cost alternatives. I'm looking at damping some engine noise, some vibrations and a lot of rear axle noise. This information is exactly what I was looking for.

Thanks again!

John


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PostPosted: January 9, 2019, 1:06 am 
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Is there some kind of foam panels that doesn't put off toxic fumes in a fire like the foam panels you buy at the Big Box stores?

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