Sound Control: General theory and Pinz specific issues.

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VinceAtReal4x4s
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Sound Control: General theory and Pinz specific issues.

Post by VinceAtReal4x4s » Thu Dec 24, 2015 4:54 pm

Sound or noise control is a big subject in the exotic 4x4 world. Home-grown and random ideas as to what might work to reduce noise often hurt the value of these vehicles, or is not very effective when the costs are weighed out. Reducing sound has been a sort of weird hobby of mine, as well as business in the past when building up custom 4x4s for a paying clients. I'm going to share what I know here based on actual experience, training and exposure to professional sound control products and their application in real world vehicles.

You will never get to the level of a quiet car or modern SUV but you can at least get half way there, or maybe better. Noise causes stress and is a major safety issue! This is why it's important and why noise pollution overall is vital to controlling in all of our environments.

THE NOT SO GOOD METHODS:

- My own #1 rule is to never use anything that could promote rust or hide a corrosion problem. I think it's very dangerous to use any "bedliner" type of material on horizontal surfaces. I have seen many 4x4's ruined this way, starting back in 1992 when I dove deep into the world of older Land Rovers. The Series and Defender models are very loud and some people tried to quiet the interiors this way. All it takes is a microscopic hole in that "paint" to let O2 and H20 do their thing and a few years later, you can be looking at a very costly and time consuming rust repair, or you may even end up with a parts truck! Have you tried removing that stuff before?! Don't make the next guy have to do it.

Also, rust often starts on the other side of that piece of metal but you may never know it because the bedliner is covering it up, as well as making it appear to be structurally sound.

- I have seen a lot of "stacking" over the years as well. This is what I refer to when guys will buy a ton of vibration dampening sheets (Dynamat, Rattle Trap, etc) and put it on everything in layers, which is kind of like trying to put out a brush fire with loads of gravel. Along the same lines, rubber mats and vinyl trim have been applied in the same way but none of this usually satisfies. In theory you can get some results from this stuff alone but the final results, weight addition, money spent and risk of hiding corrosion isn't usually worth it.

I'm sorry but it has to be said: Nothing made for the roofs of houses or hotwater heaters is going to be practically effective in managing noise in a 4x4.

WHAT REALLY WORKS:

The engineers who do this stuff for big auto companies and other industrial applications know how sound propagates in a vehicle and over the years materials and techniques have been developed to deal with this specifically.

Air is what allows sound to move. With no air, there is no sound. All noise control techniques involve blocking air or keeping something from making air move. We generally talk about noise in a car by splitting it up in frequency. Lows, which you feel in your chest and by touching the surfaces that produce them, and you can hear some of them as well (tire rumble, vibrating metal, bass).
The mids, where a lot of voices are and you can hear all of (road noise, wind, engine).
And the highs, which can really annoy you (whistling and gear whine!).

It's proven that some sounds on the extreme low or high can affect you subconsciously even though you can't fully hear them.

1- Vibration dampening This is the foundation of noise control treatment and really helps lessen your lower frequencies. There are a ton of these materials on the market. I use the Rattle Trap or the Dynamat brands. The bad thing about this stuff is the marketing. These are only one part of the process but they often make it sound like this is all you need; absolutely ridiculous!
Rattle Trap 710K.jpg
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Above is a 710K ceiling being treated with Rattle Trap. This was covered over by custom trim panels which were then auto-carpet covered.

These dense sheets of flexible, rubber/asphalt type materials effectively increase the mass of whatever they are applied to and will keep them from vibrating so much, thus reducing the noise they produce and re-transmit. They do this well but they add weight and hide corrosion. They should not be applied to the floor. I use them on ceilings, walls, engine covers, some wheel wells, behind dashes and door skins. Always make sure they are applied over perfectly sealed/painted surfaces and use a heat gun and roller. Total coverage is not needed. Around 30-50% coverage is the goal. I double up on troublesome spots.

2- Sound barrier or blocking This is probably the most effective overall material in the process but I think it's the least applied and understood. This stuff is basically a dense "mass loaded barrier" sheet that is "decoupled" from its surroundings by a layer of foam. Dynamat makes some under the name DynaPad. Cascade Audio also makes a series with names like VB-4, VB-3, etc.. they all work the same and literally block sound waves from coming at you. They do this by suspending a heavy, dense layer of vinyl (or lead) with foam which is designed to lay on the floor with no need for glues, etc. It works really well when carpet is glued to the top of it. It usually weighs 1lb per sq. foot so the weight additions can add up fast. Cascade makes one called VB-4.5 which I used in part of my Gwagen. It is .5lb instead and is very flexible. Their lead-lined stuff is great but its very expensive.
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Above is a 300GD Gwagen getting a full floor treatment of VB-4.5 and DynaPad. The shifter area was covered as much as possible to reduce sound from getting past the control openings. The materials on the floor should always overlap so no air gaps are possible.

The key is total coverage and an "air-tight" approach. It should cover every bit of flooring you have, including under the seats and should not have gaps or holes except where 100% necessary.

Another older but effective material I use sometimes is Thermo-Tec. It is about 3/8" thick and is a mat made with syn. fibers with an aluminized outer layer. I use this as a backing for carpet and works great when you lay this over a high-end material like Dynapad. It's also a great heat barrier and costs very little compared to the other stuff.
Gwagen 300GD carpet VB-4.5 small.jpg
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Above is a Pinzgauer's floor after being covered with a product similar to the VB.

3- Sound absorbing This is rare to find done correctly in auto builds. It's used extensively on planes and the new bullet trains and should be part of any 4x4 build I think. The most effective material for this is 3/4" to 1" Melamine foam which can absorb 4K Hz and above. If you can find it, Hydrophobic Melamine is the best since it won't absorb water. This is ideal for cavities in walls and behind trim, etc.. Unlike any other material, it will actually help to absorb the mid/higher sound waves around it.

In the sound absorbing category you also have carpet or any porous outer trim, like headliner fabric. This is very important!! These materials are the final straw for annoying noise. They very effectively keep sound waves from bouncing all over the place. Your ceiling is a major factor in how much noise gets to your ears. Ever notice how quiet a soft top is with the top off (other than the wind and outside sounds)? All that noise we are trying to control just beams up into the air when there's no top to reflect it.
Volvo C303 carpet.JPG
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Above is a Volvo C303 that just had a custom headliner panel made. Under it is Rattle Trap to keep the roof from vibrating, in the middle is a sound absorbing and waterproof foam (in this case, Dynamat's HoodLiner foam) and an auto-grade carpet was applied over the panels for a night and day difference in the noise levels.
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Above is the 710K's rear ceiling finished.
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Above is the 710K's finished front cab. The floor bottom was left alone in this case but the area behind your leg was treated with Rattle trap and covered with carpet. A small patch was added beside the transfer shifter. I have preferred the shop make that a little more finished looking but the budget was very tight.


So these are the basics. You need to reduce your lows, mids and highs by dampening, reflecting/blocking and absorbing, and you want to do this without sealing up your floor where rust WILL hide out.


The Pinzgauer, especially the M models with their soft tops, have unique issues.

The ceiling really needs something to absorb the sound. Aftermarket tops are the best but an expensive solution. Some people have made their own, soft under-layer. Anything you can do will help massively in keeping those mostly high-frequency sound waves from bouncing back at you.

The floor in the back: A sound blocking material goes here. I used the 1/2" Barrier matting material from http://www.heco.net/noise.html with great results before. The key is also to cover the sides as well, and keep that air-tight coverage thinking in mind.

The major treatment areas up front are under your seats, the engine cover and the doors. I lined an engine cover on the inside and then had an upholstery shop cover the outside with great results.

You can also block a lot of noise by making a barrier to block the bed area from the cab. The stock flap is thin and doesn't do much. You can modify that or make your own. Again, keeping that air-tight approach in mind.

And if you haven't already and for the sake of noise and safety, GET RID OF THOSE MILITARY BIAS PLY TIRES.

This post is also in the Tech Sessions but I thought it should have a copy here.
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Re: Sound Control: General theory and Pinz specific issues.

Post by NEWFISHER » Fri Dec 25, 2015 11:21 pm

Thanks for posting this. Im in the middle of " what to do to the new Pinz to make it quieter" stage and your experience is very helpfull. Any links to the trusted suppliers of the products you use?

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Re: Sound Control: General theory and Pinz specific issues.

Post by VinceAtReal4x4s » Fri Dec 25, 2015 11:44 pm

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Re: Sound Control: General theory and Pinz specific issues.

Post by carbon60 » Fri Apr 15, 2016 12:13 pm

I would like to say thank you for posting such an in-depth discussion of these techniques! Very helpful.

A.

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Re: Sound Control: General theory and Pinz specific issues.

Post by Brickren » Sat Apr 16, 2016 7:15 am

I just bought tires from Treadwright. What a difference. I had Biasd tires and never gave any thought about the ride. It is a military truck, right? Man, its like riding on marshmallows. Ride is softer and grip is better. Pulled a Chrysler 300 out of ditch where car was on its side. Road was icy. I bought their tires with glass and walnut shells in the rubber compound. Yanked car out with minimal wheel spin. 300 weighs same as Pinz, I think. Steering harder at slower speeds, like sitting still. Just keep moving. Wonder what added strain on steering gear.
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Re: Sound Control: General theory and Pinz specific issues.

Post by Jimm391730 » Sat Apr 16, 2016 12:22 pm

Wonder what added strain on steering gear.
Having had several different tire sizes on my Pinzgauers over the years, I can say with certainty that wider tires steer harder (A LOT harder!). You can compensate with higher pressure in the fronts; for example, I run 60psi in the front of my 712W for on road use.

When I bought 8" widened rims for the 712W, they came with 295/75R16s on them. The steering was so hard that I thought something had broken, and I was worried that I couldn't stay on the a winding mountain road - it was that hard to steer. Now I've changed back to 265/75R16s (also from Treadwright) but I also looked at the tread width - for example, their "Claw" has a 9.5" tread width, but their "Warden" tread pattern has only an 8.5" tread width for the same size tire. At the time, they had their "Guard Dog" tread pattern available and that's what I got. Narrower tread makes steering much easier, regardless of the official size rating.

Our 710M got their tire version with the "Kedge Grip" for winter, like you have. While our last few year's winters have not been bad, we have not needed to chain up and my son now has fun driving it around in the snow and pulling out vehicles that are stuck. I got the regular tires on the 712W, as the weight and extra axle helps compensate in the winter.

When these wear out (and they are wearing at least as well or better than virgin tires) I'll get more from Treadwright. We've had them 4 years on the 710M and 3 years on the 712W. Their tires are half the price of new, and work just as well.
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Re: Sound Control: General theory and Pinz specific issues.

Post by itsalljake » Sun Jul 10, 2016 1:21 pm

Really great to information Vince, spot on description of sound wave cancellation. Thank you for all the vendor info as well. You repeatedly mention using caution when covering flat (bottom) surfaces to over rust cover, how did you attach the floor panels in the cab, are they affixed or removable?

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Re: Sound Control: General theory and Pinz specific issues.

Post by VinceAtReal4x4s » Sun Jul 10, 2016 2:21 pm

Are you referring to the floor pics above? That is in a Gwagen and when the seats are bolted back in, it holds down part of it. The area where your feet go is held in place because of the weight of the material, just like the floormats. It is sort of tucked around various irregular floor parts that hold it in too. In the case of a roll-over, part of it might fall but if that ever happens I have other issues to deal with. Being able to take everything out easily is essential for cleaning and drying in case of deep water or big spills.

In the case of the 710K, the rear material was mostly held down by it's own weight. In the front, the area behind your leg was well cleaned, dynamatted and then they used glue for the carpet. The roof was the same thing.

I will add 710K pics that I forgot about above.

Here's a pic of the back floor. The floor liner is the stuff from Heco and it's just laying there. It's dense and fairly heavy, like thick rubber, but it insulates sound, unlike solid rubber. And yes, after doing all of this I really wanted to have the seat brackets painted and seats recovered but that would have been way too expensive for that build.
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Re: Sound Control: General theory and Pinz specific issues.

Post by Jake2015 » Thu Sep 14, 2017 12:53 am

Vince, in the last picture of the 710K rear, is the floor mat the 1/2" Composite Barrier Floormat (07652-Black) or the 1/2" Floormat (07661-36" wide) (or 48" or 60")?

Also, is the carpet covering the sides and top of the wheel wells glued? Is there anything under the carpet?

Thanks for the great information. I need to quiet my 712K. I'm thinking of doing the cab first and as you suggested changing the curtain between the cab and rear area to something better to block the rear sounds coming forward. Then tackle the rear when more funds are available. Any suggestions for the curtain material?
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Re: Sound Control: General theory and Pinz specific issues.

Post by VinceAtReal4x4s » Thu Sep 14, 2017 2:06 am

It was the 1/2" floormat material from Heco (it's high quality stuff). Sorry I don't recall the width. The middle floor area was covered with the composite mat. The issue when buying is there's no way to order exactly what you need given the coverage needs. That's why the middle material where the passengers feet would go have the binding strips. We cut out what was needed and bonded a leftover piece to make it work. It ended up looking kind of nice though, I think. One of those strips is just for looks so it matches.

My thinking on using the floormat stuff for the back/cargo area was the length-wise ribs made sliding equipment in easier than the composite surface would have. In hindsight I may have ordered all floormat material. I guess I was worried about the ribs coming out uneven when I knew we had to cut/fit that middle part of the floor plus the ribs seemed like they'd trap dirt from shoes and might be harder to clean out. The budget kept me from ordering anything over the bare minimum so I couldn't play around at all.

Keeping in mind that the wheel well areas were 100% free of surface rust and fully painted, yes that area was glued in spots although not heavily; it could be removed without much work. Yes there was some Rattle Traip applied underneath but only on the vertical section where rust would be very unlikely to start. I think the pieces were about 7" by 12" and may have been doubled up since that is a fairly "tinny" area. You definitely don't need full coverage on any panel to stop vibration. I probably covered about 60% of it overall.

If I had the budget, I would have ordered the floormat barrier or VB liner to put under the carpet, and glued the carpet to it instead. The weight and seat/seat-belts, etc. would pretty much keep it down. You could just do a few spot glues then or velcro tabs, or even another mechanical bond of some kind. I had the idea that for next time, I'd embed rare-earth magnets into the edges/corners. I had some window curtains made like that for camping, with the magnets sewn-in, and it works great.

The cab curtain would be nice if you made it from the sound blankets made for industrial shops to isolate loud tools/machines and service areas, which is a quilted fiberglass-based material. It would block and absorb unlike the stock curtain. An upholstery shop could cut put a window in the middle. Sewing magnets into the bottom might be a good way to seal it up quick, or velcro it. Enoise has them http://www.enoisecontrol.com/products/sound-curtains/

I've done 4 sound jobs on "K's" over the years and never seem to have the budget to really do it right. The upholstery shop, plus my time and materials all can add up quick so I understand but I think sound control is as important as seat belts, brakes, etc.. I'd love to really give it a try just once with the budget needed and do some sound measurements before and after to prove the benefits once and for all. I can dream. :?
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