Questions about blocking 110 Hz in a car via Green Glue - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 21 Old 08-25-2019, 04:05 PM - Thread Starter
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Questions about blocking 110 Hz in a car via Green Glue

My car, a newish Corvette, has a steady drone noise of about 110 Hz. A major noise contributor is the 4' x 4' floor under the hatchback. I want to install a noise suppression layer between the carpet and the hard layer (maybe it is fiberglass) below.

Most auto noise suppression is a soft butyl or vinyl layer with a thin aluminum top layer. Most of them are only about .08" thick. The soft layer is adhesive. It seems there is a lot of BS in auto acoustics, little data, and some placebo affect. Also, I think most aftermarket auto noise suppression assumes a need for full frequency noise suppression even though low frequency noise is more prevalent. On a more positive note, most people are happy enough with the results of using the common auto films but I believe there is room for improvement.

Last year I considered building a quiet box for a generator and for that project I read about sound blocking using Green Glue and drywall. It makes perfect sense to me. For the flat trunk surface in my car I think green glue and a thin layer of Hardboard or MDF would be much more effective because Green Glue and air would be a much better sound blocker and MDF would have much more mass than the auto films like Dynamat for example.

I posted this here because I wanted to get away from knee jerk responses from auto forums and people here are more familar with the green glue method.

Thanks for listening! I appreciate any comments.

PS: I realize I will need to apply noise suppression elsewhere in the car but first I want to tackle the main culprit.

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post #2 of 21 Old 08-25-2019, 07:45 PM
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Actually I use Dynamat Extreme (or equiv knock offs) on sheet metal ducts/furnaces to quiet them for theater projects. It works VERY well to reduce sound transmission. You could even do multiple layers if the first doesn't do the job. I actually think it has more mass per cu inch then MDF/hardwood or drywall. I also have extensive experience using Green Glue and I would grab a bunch of the self adhesive mass loaded vinyl products first.
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post #3 of 21 Old 08-25-2019, 10:45 PM - Thread Starter
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Thanks, Jeff!

I appreciate your advice because you have so much experience with both GG and Dynamat. I imagine sheet metal ducts have lots of low frequency noise like cars so that is experience is quite relevent.
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post #4 of 21 Old 08-25-2019, 10:52 PM
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Those CLD products (constrained layer damping) are mostly intended to be applied with partial coverage to stop panel resonance - by adding constrained mass to the panel which stops it from resonating at the nuisance frequency.

To stop transmission of outside noises through a panel (such as exhaust or road noise passing through a panel into the cabin), you would need several layers of CLD product applied as seamlessly as possible, like Jeff mentioned. CLD is probably still the best product for the job, due to its ability to be rolled into the contours of the panel and then have the factory finish (plastic panels, padding, carpet) placed back over it for a factory appearance.

On a sports car there is typically less or no factory sound deadening compound applied, to save weight. Sound deadening compound on a floor pan for example would be a thick layer of tar-like substance applied to the whole panel, which then is concealed (and aided) by padding and carpet.

It sounds like you would need at least a few layers of CLD product applied in full coverage to your trunk floor to net the same effect. Use a roller to get it into the contours of the panel, try to butt your seams as neatly as possible, and foil-tape the seams on the last layer to keep the goo constrained.

I bought some "Noico" brand (search it on Amazon) 50 mil butyl rubber CLD product for one of my cars but have yet to install... has great reviews though. Looking at Amazon now, it seems mostly 80 mil thickness is what they sell now. The Noico stuff has a pillowed appearance to the foil, so you know when it is properly rolled into the contours of the panel (the pillowed foil flattens out).

One of these days I'll be done (or done enough) with the theater to get back to my car projects....
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post #5 of 21 Old 08-25-2019, 11:17 PM
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Quote:
Originally Posted by dugt View Post
My car, a newish Corvette, has a steady drone noise of about 110 Hz. A major noise contributor is the 4' x 4' floor under the hatchback.
Why? Is it actually that panel buzzing? Or (like my old 5.0) is it an exhaust effect? If you put the windows down, where is the drone coming from (because if it is really the panel it will still just come from there, but if it is louder with the windows down it is probably exhaust). Is the drone the same at all speeds or is it rpm-related? (The 5.0 resonated at around 1700 rpm, which was highway speed, SO annoying) I ended up modifying the exhaust, it was the only way to get rid of the resonance because it came through various panels and through the air. Soundmat and such *might* help, but 110 Hz is a fairly low frequency, hard to stop.

I'd also look on Corvette forums to see if others have the same complaint and try posting in a car audio forum(s), you will likely get better answers.

Oh, try putting like a blanket and a heavy bag of mulch or dog food or whatever on the panel. If the sound doesn't change, it's not the panel. You could also temporarily stuff sand bags back there-if that doesn't stop the sound, all this damping won't be able to help either.
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post #6 of 21 Old 08-26-2019, 08:43 AM - Thread Starter
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Thanks, James for the suggestions. Noico looks like a good a value and has a real good review score so I’m and verge of buying some.

Thanks for the questions Head_Unit. My car doesn’t have any unusual buzzing. It has typical road noise without suppression. It has little engine noise or wind noise at my usual speeds.

I’ve read a lot of posts on the Corvette Forum and most of the people who have done anything to suppress the noise are happy with the improvement. Some just use an aftermarket multilayer foam mat on the cargo area and behind the seats. Many have full padding using CLD like Dynamat. The few who have measured the difference have achieved a decrease of as much as 5db.

The Cargo area is like and echo chamber and it is right behind the drivers head. Also, the rear wheels are right behind the seats and the tires are huge, 285 R35 20”, and sticky so the generate a lot of noise. Actually, I’m surprised the car isn’t noisier. In this latest generation of Corvette, Chevy has reduced the noise.

I bought a sound level meter and have taken several measurements without cushions and with lots of cushions in the cargo area and behind the seats. The foundation of the cushioning was In the cargo area was a big thick heavy sofa seat cushion and then I used pillows over the wheel wells and to fill in the voids. This is before I realized that they noise is about 110 Hz and that nothing absorbs that low frequency. The result was a noise decrease of 6dBC at 50 mph. I can clearly hear the improvement so I decided to do something more permanent.

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post #7 of 21 Old 08-26-2019, 10:15 AM
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You could add some bracing to the panel, which should drive the resonance frequency up and make it easier to attenuate.
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post #8 of 21 Old 08-26-2019, 10:58 AM - Thread Starter
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Quote:
Originally Posted by impreza276 View Post
You could add some bracing to the panel, which should drive the resonance frequency up and make it easier to attenuate.
Do you mean I could add cross members to the hardboard if I use the green glue method? Here is a photo of the rear interior. The floor already has kind of a corrugated structure. On the bottom of the hardboard I could put braces that would fit into the deeper parts of the floor.



I think the photo didn't get included but hopefully I got my point across.
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post #9 of 21 Old 08-26-2019, 11:27 AM - Thread Starter
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The braces idea made me realize that mass suppresses noise because it resists vibration. Braces do the same thing. Other vibrating parts in cars might benefit from anything that would help it resist vibration. For example, putting foam rubber under plastic panels so that it pushes out on the plastic panel to keep it from vibrating or a long carbon fiber strip attatched to the inside of a door panel. Or, a small piece of aluminum angle iron.

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post #10 of 21 Old 08-26-2019, 12:06 PM
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Bracing breaks up one large resonating surface into several smaller ones that will resonate at a higher frequency.
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post #11 of 21 Old 08-26-2019, 12:14 PM - Thread Starter
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Originally Posted by impreza276 View Post
Bracing breaks up one large resonating surface into several smaller ones that will resonate at a higher frequency.
I would think it would loose some energy in the process and to get to my ears itt would have to go through carpet on the floor and some of it would bounce around in the back before it made it to the front seats. The rear window is extremely sloped so it is likely to get bounced back into the floor.

Actually the front and rear window are both extremely sloped so there is a lot of glass for a small car. That doesn't help.

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post #12 of 21 Old 08-27-2019, 08:16 PM
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What I used to do with cars.......is pull back the carpet/insulation, and plastic panels, and paint the metal with elastomeric roof coating/paint, and then put a pad of half-inch open cell foam over that, and then replace the carpet/panels.

The only bad part - because of the "paint", the car will smell for a month or more, you'll have to roll down the windows when you get in for awhile, until the "paint" cures. But it was cost effective.

Today I would probably use constrained layer paint with microballs. When the balls vibrate, they convert vibration into heat. Pysics 101 tells us we can't wave a magic wand and eliminate vibration/unwanted sound. The best we can do is convert as much as we can into heat.

Or just buy a Cadillac and most of the soundproofing is already done! lol. That '95 Seville I had was really quiet. It would make a great car for a stereo.

A cargo van might be another great vehicle to put a stereo in - there are less windows to reflect sound.
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post #13 of 21 Old 08-28-2019, 09:49 AM - Thread Starter
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How effective is the noise supression of rubber foam between a thin surface vibrating at 110 hz and another thin surface. In my car there are plastic panels that cover the noisy 110 Hz unpadded wheel wheels. I'm going to add CLD Noico to the wheel wheels and maybe to the plastic covers too but I think putting foam rubber, the spongy stuff, between the surfaces would be very effective at dampening the vibration of both the wheel well and the outer panel. Agree or disagree?

Thanks.
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post #14 of 21 Old 08-28-2019, 10:33 AM
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Drone is typically exhaust related.. Did you put an aftermarket exhaust on your car?
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post #15 of 21 Old 08-28-2019, 10:45 AM - Thread Starter
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Drone is typically exhaust related.. Did you put an aftermarket exhaust on your car?
It is a stock Corvette. I'm pretty sure it is road noise because it is much louder on textured cement and almost quiet on fresh smooth asphault.
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post #16 of 21 Old 08-28-2019, 12:01 PM
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It is a stock Corvette. I'm pretty sure it is road noise because it is much louder on textured cement and almost quiet on fresh smooth asphalt.
Have you checked your tires? Are they cupped? Doesn't seem like a mass produced car would have this problem and from my quick search, no one else is having it..

Must be another contributing factor to it.. Before going and tearing into it, look at the usual culprits of cockpit NVH/Drone..
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post #17 of 21 Old 08-28-2019, 12:25 PM - Thread Starter
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Have you checked your tires? Are they cupped? Doesn't seem like a mass produced car would have this problem and from my quick search, no one else is having it..

Must be another contributing factor to it.. Before going and tearing into it, look at the usual culprits of cockpit NVH/Drone..
PrciseD, have you driven a high performance sports car? They are mass produced but they light and fast and LOUD. My tires are almost new and more quiet than the run-flat tires they come with. Some like the loudness of stock Corvettes but many owners insulate them to make them more quiet.

I could post a dozen links to threads about adding sound insulation to a Corvette but I'd rather talk about my foam idea.

"How effective is the noise supression of rubber foam between a thin surface vibrating at 110 hz and another thin surface. In my car there are plastic panels that cover the noisy 110 Hz unpadded wheel wheels. I'm going to add CLD Noico to the wheel wheels and maybe to the plastic covers too but I think putting foam rubber, the spongy stuff, between the surfaces would be very effective at dampening the vibration of both the wheel well and the outer panel. Agree or disagree?"
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post #18 of 21 Old 08-28-2019, 01:23 PM
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PrciseD, have you driven a high performance sports car? They are mass produced but they light and fast and LOUD. My tires are almost new and more quiet than the run-flat tires they come with. Some like the loudness of stock Corvettes but many owners insulate them to make them more quiet.



I could post a dozen links to threads about adding sound insulation to a Corvette but I'd rather talk about my foam idea.



"How effective is the noise supression of rubber foam between a thin surface vibrating at 110 hz and another thin surface. In my car there are plastic panels that cover the noisy 110 Hz unpadded wheel wheels. I'm going to add CLD Noico to the wheel wheels and maybe to the plastic covers too but I think putting foam rubber, the spongy stuff, between the surfaces would be very effective at dampening the vibration of both the wheel well and the outer panel. Agree or disagree?"
Yes.. I know a thing or two about fast cars.. I've built a few of them and have an Audi with 580 AWHP that loves to eat V8s lol.. hell my wife's dual pulley supercharged Q5 keeps up with some of them..

I was just saying that there might be another reason you have the drone and trying to point out some things..

But hell, what would I know about adding green glue to cars in a dedicated HOME THEATER BUILD FORUM...
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post #19 of 21 Old 08-28-2019, 03:39 PM - Thread Starter
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Yes.. I know a thing or two about fast cars.. I've built a few of them and have an Audi with 580 AWHP that loves to eat V8s lol.. hell my wife's dual pulley supercharged Q5 keeps up with some of them..

I was just saying that there might be another reason you have the drone and trying to point out some things..

But hell, what would I know about adding green glue to cars in a dedicated HOME THEATER BUILD FORUM...
So you have two luxury cars with big engines. Is that why you assume Corvettes are quiet? My Audi A6 twin turbo was the quietest car that I have owned. Since you didn't say that you have not driven a high performance sports car, I will assume you haven't and that's fine. I'm new to Corvettes but I've driven 5 stock Corvettes in the last month and four of them had a lot of road noise but one of them was fairly quiet and it had a lot of Dynamat. I'm working in that direction and considering options.

I assumed that a lot more people in this forum know more about green glue than those in my favorite Corvette forum so I posted my green glue question here. I also posted it here because I've been registered in this forum for a couple of decades.

I appreciate that you were trying to help and thanks for bouncing my thread.

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post #20 of 21 Old 08-28-2019, 07:08 PM
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Was thinking tires but seems you've replaced stock. Suspension can of course be damped more by installing aftermarket softer bushings but at the cost of performance. Corvette owners aren't too keen on that. Least impact on performance will be a little weight addition so I think you're on the right track. Not sure I'd go with green glue though. Stiffen the panel to break up and raise the resonance, then add dynamat to damp what is left. Stiffening can be done by epoxying in a metal or composite rod or bar. Cover with dynamat.
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post #21 of 21 Old 08-28-2019, 09:27 PM - Thread Starter
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Thanks, Bigus. I will definitely continue with Noico.

Although I think most of the noise comes from the wheel wells, maybe the middle of the cargo floor is a major culprit. I just spent some time tapping the whole cargo area and the middle of it produced the lowest frequencies which makes sense because it is the biggest drum. Am I correct in thinking that it is probably a major transmitter of the low frequency noise? The blue line outlines the spot. It would probably benefit the most by stiffening. I think I'll put strips of OSB in the horizontal wells and two strips of OSB running front to back.

Here is a photo of the cargo area.



There is a light plastic cover that goes over the electronics in the lower section of the photo. It has a somewhat dull thump to it. It might be a good candidate for some stiffening too. I will put a lot of Noico in the center of all of the flat sections throughout the cargo area.

Above the cargo area there is thick carpet padding with carpet on top. It is my understanding that those matterials aren't effective low frequency dampening except for the added weight. Whatever I do I will put it back on top.

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