Quest for Quiet - Sound Deadening Secrets Backed by Data

[J-Gaz.]

Let's collect some data.

I didn't see a 'Sticky' on sound deadening anywhere, or a forum category - so, since I've got a 70 beetle, I'm posting here...

Sound deadening and sound absorption seems to be a scattered subject with lots of threads. I’ve read most of them, and the one thing I never see is ‘Data’

In this post, I want to outline 2 things, then ask for help.
Understand Decibels
Define sound deadening, decoupling, and sound absorption.
DATA: Track results and Your setup (This is where your participation is needed)

Everyone seems pleased with the job they did to quiet down their ride - but I also don’t see a lot of folks redoing the work if it’s not up to par…

No Mulligans. And the results could just be confirmation bias without seeing any data...

So whether you used Fatmat, DynaMat, Lizardskin, or QuickRoof etc - I want your numbers.

If you are in the middle of a project, you can do Before and After - otherwise, let's find out what you’ve got now, and how it’s working - especially you stock guys.

Before we get to measuring what you’ve got, I wanted to outline my understanding of sound deadening and sound absorption. Most of the info I have ready falls back on ResoNix and CarBuilders. But I think its good to go over, because it seems like a lot of folks are going overboard and not getting the results they hoped for. From what I’ve seen in the forum, we see a lot of panel deadener applied, but not much sound absorber…
I’ll be doing my 70 beetle here shortly, which is the reason for my research and this post.

Understanding Decibels: The Decibel scale is measured logarithmic instead of linear. Every 3-decibel change, the energy is doubled or halved. So if you are at 85 dBA driving, and work to get down to 82 dBA, You’ve halved the energy transfer. That being said, you don’t need to see too big of numbers to get results. If you can get 10 dBA less out of your car and insulation job, you crushed it.

Sounds at or below 70 dBA are generally safe for your hearing, even after long exposure. However, prolonged or repeated exposure to sounds at or above 85 dBA can cause hearing loss, and the louder the sound, the faster hearing loss can develop.

So the goal should be to get to 70 dBA or less.
Now, most of us don’t have the instruments to measure both Decibels and the electroacoustic equipment to measure Noise, Vibration, and Harshness (NVH) or Sound pressure level (SPL) - measured in dB.
But there is a Phone App that will measure dBA which is a type of decibel measurement that takes into account how humans hear sound which we’ll address later.


Define sound deadening, decoupling, and sound absorption.

There are 4 basic components to sound deadening and Sound insulation.

Sound deadening panel vibration deadener
Sound Decoupling between vibrating panels
Sound Absorption aka Jute/ foam
Sound Blocking Aka Mass Loaded Vinyl

1. Sound deadening - Tarboards/ Butyl
The purpose of the tar boards is to take the resonance out of large panels that vibrate or reverberate. This can be exemplified by imagining a cymbal on a drum set and striking it with a drumstick. Now imagine you put Some kind of adhesive dampener on it. It won't vibrate or resonate nearly as much. It only takes about 20%-30% coverage to make a marked improvement. FatMat says more is better.
At a certain point, you get diminishing returns and just added weight. This is why even in new cars, they are not lined top to bottom with sound deadener. Its a balance of weight, cost, and diminishing returns.

2. Decoupling
To carry on with our cymbal example, now imagine placing a foam, rubber, or vinyl gasket between the cymbal and the cymbal stand. How much change will you notice? Probably not much - but what will happen is that Cymbal Stand will vibrate less. There will be less transfer of energy. Although we might not hear the difference, there will be less harshness and hertz measured even if we don't hear it. It’s further displacing energy.
That is decoupling.
You can do this in your car by placing a decoupling layer between panels and door cards. Some people add this between their base layer of Sound deadener and their Sound absorption layer. What closed-cell foam decouplers do not do, even though many companies claim this, is reduce, absorb, and/or block noise. It does NONE of those in any meaningful way, shape, or form. Beware of companies that advertise their CCF products as being able to do this. They are preying on the ignorant. A quick summary of why they do not block or absorb noise is that you need a lot of mass to block noise, and you need open cells or a fibrous mat to absorb sound.


3. Which takes us to sound absorption.
Why the OE uses Jute.
Using the example above, now imagine throwing a moving blanket on top of your cymbal and stand, then striking the cymbal with your drumstick… How much quieter is that?
That’s the Jute. Wolfsburg West sells a Jute parcel tray kit that’s a 1/2 inch pad with a tar paper layer in the center. The tar paper acts as a decoupler, and the jute acts as a sound absorber.


4. Sound Barier/ Blocker MLV
This stuff is heavy. This is the final stage in a lot of sound-deadening builds. This is a sound “blocker” the versions that are most popular are just vinyl - which should have a foam decoupler as noted above. Or, vinyl with the decoupler (Closed Cell Foam) integrated.
There is a lot of information about MLV and its need to be 100% coverage in order to be effective. I found a chart from "The Science of Sound, Third Edition" by Rossing, Moore & Wheeler showing that 98% coverage, which is very hard, the transmission loss is only about 17 dB.
90% coverage, and you are at 10 dB of transmission loss.
80% coverage, and you are at 7 dB transmission loss.
50% coverage and you are at a not easily noticeable 3 dB of transmission loss.

Outliers:
None of this will account for Tires, old door seals with gaps, or crusty window seals and air noise. Dont forget that gaps in your dash will add wind noise too. Plus, you all know that fresh tarmac is loads quieter than an old concrete section of highway. Even still, it’s helpful to know where you started, and what the improvement actually happened.

So why bother?
Because.
Some folks may be running similar setups and get similar results, which will tell people about to tackle the project what results worked best so they can attempt to emulate and know what to expect.

Examples:
If someone installs Quick Roof, then OEM Jute and carpet they may get X dBA results.
Where if a few people are running the DEI kit, it may Equal Y dBA results
And if a few people are completely stock and all get around Z dBA results, then at least people will have some averages to work with when deciding which direction to go.
That’s the hope anyway.

Your turn: Civilian Science and DATA.

Here’s what I’d love to see - could some folks here take their cars for a spin this week and measure the decibels in their car as they go 20 in town, and then 60 or so on the highway? Then report back your numbers with what you did for your motor, exhaust, and your method of sound deadening.

If you are using an iPhone, the NIOSH SLM app is fairly consistent. Although not a finely tuned instrument, if you are just comparing it to itself, you should be able to see some consistency.

For example my car right now:

1970 Beetle.
Stock 1600 Singleport w/ extractor exhaust.
New pans and luggage tray raptor lined top and bottom w/ no No sound deadener.
Stock headliner, stock Quarter, and door Cards w/ the OG door Tar dampener.
Stock Tarboards in the engine compartment.
Cut outdoor carpet with rubber bottom in the rear luggage/parcel tray, the floors (like floor mats), under the rear seat, and under the front bonnet.

Idle 58 dBA
20 MPH - ~70 dBA
40 MPH - ~75 dBA
60 MPH - ~80 dBA

One thing to note is I didn’t notice any decibel change between fresh tarmac or old concrete on the highway - but the Harshness was audibly evident. It seemed much louder even though it didn’t register. This is likely a change in what Hertz and frequencies are being transmitted. But again, I don’t have the electroacoustic equipment - a Sound Power Meter, Noise Dosimeters, Noise Nuisance Recorders, or any other equipment to measure the different Hz that are being transmitted other than this decibel app I mentioned earlier…

Compared to my Stock 2009 For Escape Hybrid
20MPH - ~ 60dBA
40MPH - ~ 66dBA
60MPH - ~ 70dBA

Your turn - what do you got, how is your interior Treated, and what are your Decibles? Thanks!
_________________
1970 Beetle | Basically Stock 1600 SP

[Puppy67]

It could be a while (couple of months maybe), but once mine is back on the road I'd happily do measurements with the bare shell then each stage of sound deadening/decoupling, etc as it's added.

In the meantime I'll keep an eye on this to see if my current plans are good or if there's better.

[J-Gaz.]

[KTPhil]

Lots of topics on the samba:
https://www.google.com/search?q=thesamba.com+sound...UTF-8#ip=1

They are just mostly in forums for other models.
_________________
Current Fleet:
- '71 Fastback
- '69 Westfalia
Retired:
- '67 Beetle
- '65 Beetle (x2)
- '65 Bus
- '71 Squareback

[MuzzcoVW]

Another thing to add to this equation is engine size. I just went from a 1585 to a 1776cc in my bug. Everything on the engine, intake exhaust etc is the same. Just the increase in CCs has made the car noticeably louder inside. I don't have a way to measure, so it's just by ear. I had made great strides in quieting the car inside, but now will be looking to do a little more... although the increased throatyness of it is quite nice

[jeffrey8164]

Keep chasing the dream I suppose.
You’ll never make a Beetle/Ghia/Type 3/Bus as quiet as a more modern car.
I put dynamat all over everything when I built my Ghia. The most I think it did was to not make it sound like a tin can when I tap on it or close the doors.
There are just too many cavities in the body of these cars.
I do have a 2276 and it’s only mildly quiet at idle.
If I open my rear 1/4 windows it gets even louder.
I can’t compare before and after as the car wasn’t started until completed and ready to drive to the alignment shop.
_________________
Volkswagen!
Turning owners into mechanics since 1938.

“Let he that is without oil throw the first rod”
(Compression 8.7:1)

[J-Gaz.]

[J-Gaz.]

[moundtop]

If you are going to embark on this Herculean effort, you should begin by establishing a measurement protocol. Sound measurements are extremely sensitive to the location and orientation of the measurement sensor.

I would recommend the following:
Place sensor at the top of the steering wheel and orient it so that it faces the passenger side window. Conduct the test with all windows rolled up as well as all windows rolled down. This would result in a common measurement geometry across all users.

An uncalibrated device could be used to compare the relative effects of various noise control interventions but a calibrated device (or agreed upon standard such as an iPhone running a common app) would be needed to document absolute improvements in noise level.

[MuzzcoVW]

[J-Gaz.]

[J-Gaz.]

[Puppy67]

Found this which may be of interest -


Link


My impression from this was that the butyl damper layer alone does an OK job, but 2nd layer (foam/jute layer) will do a whole load more. The echoing comment is borne out by recording studios spreading rugs and cushions around if they don't go all out on acoustic panelling, or even just hanging curtains.
I was considering mass loaded vinyl, but it seemed to do very little (maybe due to not being full coverage?), so now not so sure if it's worth it.

[J-Gaz.]

@Puppy67

I've watched this one too - very informative.
Yes, totally agree, Dampner/ butyl is just to stop panels from reverberating. It's the cymbal example I gave above and why Dynamat used to send bells to audio shops - ring the bell without the dampener, it's loud. Cut a little circle of dynamat and apply it to the bell - it dampens the reverberation. That also illustrates that you don't need 100% coverage of the butyl to get great results.

Jute and foam make the biggest difference in absorbing noise inside the cab for sure. there are some other products - latex-impregnated egg crate foam - that is supposed to be excellent as well.

Same as you on MLV - I think I need to see more numbers or how it would work. Seems like hanging it vertically to get 100% coverage would be a paint.

I was reading a Toyota form, and they guy did his roof - butyl and foam I think, and that's where he saw the most improvement... worth thinking about.

At 17:18 in the video he said what I thought was most interesting - the dBAs were virtually the same... but the "harshness' of the sound was gone. Which is why ideally we'd want to see a frequency spectrum and not just decibels. That's what I was talking about earlier. I don't have the tools to measure a frequency spectrum to see what the difference in Noise, Vibration, and Harshness (NVH) would actually be. But just knowing that, even if I don't decrease the overall dBAs, it will still change the resonating frequency and be much more pleasant to drive.

Curious to see what you decide to do. You should definitely take some dBA measurements before and after to see how well each layer works. Just remember that dBA isn't going to tell you how the frequencies changed, and that noise reduction of "only" 3 decibels is equivalent to a reduction of 50% of the sound intensity. 2dB is 33% noise reduction...

Keep us posted on what you end up doing!
_________________
1970 Beetle | Basically Stock 1600 SP

[J-Gaz.]

Puppy67

Not sure if you've already seen this video, but he also does a fair job of discussing frequency reduction, and materials to use.


Link

_________________
1970 Beetle | Basically Stock 1600 SP

[Puppy67]

[unclewede]

Using NOISH with phone held in right hand about the middle of the cabin. Although I know it's not linear, I didn't have an assistant so no decimal values. Speeds were done on similar road surface, and holding steady at the speed :

Idle: 68
20 MPH: 73
30 MPH: 77/2nd, 72 3rd
40 MPH: 74
50 MPH: 75
60 MPH: 79

77 FI, stock with muffler. QuickRoof done from the fold in the back seat near footrests to the top of the luggage rack. New insulated deck lid with speakers. New-er door cards from TMI. Can't remember if I put any QR on the doors before the cards were replaced.

For reference, when I had the radio at "normal" volume and the engine at idle, I was reading 86. . . so I really can't hear the engine.

[J-Gaz.]

[unclewede]

I don't think I even have carpet over the QR, since I can still see all my work if I take out the back seat. When we re-covered the seat, just went with foam/vinyl, no jute there either.

[J-Gaz.]