TheSamba.com :: View topic - Dynamat Sound Deadening Testing Before and After

Sat Oct 27, 2012 4:40 pm

The posts regarding sound deadening often make interesting claims about how the vehicle has been transformed. A few have tested things out and found little difference. No question that spraying 40 mil of LizardSkin on a stripped van will make a difference. How much? Is laying out Dynamat Extreme over the rear bed and under the bench seat (easy to access) worth the expense and few hours of time? I don't know, however here is post 1 with some measurements before. The results after tomorrows testing. My lab assistant is uh, at a birthday party..

First of all, the test van is a 1990 Westfalia, with auto transmission, and a 2.0L 3A audi block with Jetta head and digifant II. The exhaust includes a 2.5" cat, and two straight thru stainless steel mufflers. The exhaust uses a stock snorkel as well as silencer that I built. Horsepower on the mod'd engine is about 145.

EDIT: The app used is SignalScope Pro (~$70): http://www.faberacoustical.com/ios_apps/signalscope_pro/

iOS 6 removed the 100hz high pass filter that earlier would have been in issue with the ipad2 and iphone4gs used for testing. http://blog.faberacoustical.com/2012/ios/iphone/fi...ic-inputs/

The test (unlike one I saw previous) provide data from both the front and the back. To test, I used Faber Acoustical's SignalScope Pro on an iphone 4s, and an ipad 2. The iphone was hand-held up front, the ipad hand-held by my 9 year old daughter sitting in the rear seat (who was pretty stoked on helping her Dad geek out, ha). These devices are not calibrated aside from the default, which is close, but both devices are not reading exactly the same. Relative results however should be quite accurate. Here are the before results. Note that the front results use the FFT analyzer and the rear, the 1/3 octave RTA. Same information, different display. The FTA plot dashed lines show the max during the sample period (5-7 seconds) and are what we should be looking at.

Default input sensitivity calibration for the iphone 4s is set at 32 Pa/FS and 21 Pa/FS on the ipad2, for those wishing to emulate the tests. Defaults in place everywhere else. Edit: The RTA (bar graphs) app was set to "flat" weighting so what you see is what was recorded. "A" weighting would have changed tr results based on human hearing, essentially attenuating the low and high frequencies.

There are two test results at 60km/h, and two at 100km/h on level highway. We'll repeat these at the same locations tomorrow once the after test is done.

front seat before dynamat at 60km/h test 1

front seat before dynamat at 60km/h test 2

front seat before dynamat at 100km/h test 1

front seat before dynamat at 100km/h test 2

rear seat before dynamat at 60km/h test 1

rear seat before dynamat at 60km/h test 2

rear seat before dynamat at 100km/h test 1

rear seat before dynamat at 100km/h test 2

Sat Oct 27, 2012 4:46 pm

The pics after:

Any predictions? I'm pretty sure the wind noise up front is louder than the engine in the back. Ha.

Sat Oct 27, 2012 5:02 pm

Nice scientific approach to the question. Do you intend to also test Dynamat + closed cell foam? Awaiting your test results. Thx!

Sat Oct 27, 2012 5:51 pm

what is the freq. response of the built-in microphone?

be sure to run the same road section after as before & orient the units exactly the same

Sat Oct 27, 2012 6:05 pm

This is awesome.

Very much looking forward to results.

Two comments- congrats on having a daughter interested in your experiments and holy shit, that much dyna mat must have set you back a few loonies.

LP

Sat Oct 27, 2012 8:02 pm

Singer, wasn't planning to test foam as the mattress foam is actually quite effective in dropping noise levels, and i think would make incremental gains with closed cell foam very small. Driving without the mattresss foam is noticeably louder. Important to note my tests are with the foam in its normal position. Should also mention that the closet was fully lined/dampened with Dynamat (old stuff) to keep the 12" sub from shaking it apart. After 9 years or so that Dynamat is 100% stable.

Randy, yes same section of road, same speeds, same tests, and held identically. Hand holding made sense to me as vibration transmission would be near zero this way. The mic has a response from 20 to 20000hz. Ios6 removed the built in high pass filter at 100hz which just now makes the onboard mic useful: http://blog.faberacoustical.com/2012/ios/iphone/fi...ic-inputs/

LP, my wife suggested i ask my daughter to help...and what a great way to include her in some real world science. She took her job seriously, including managing the capture. saving the data, and following our "scientific" method. We stopped after the test, compared results and discussed why we were seeing them. Not bad for a 9 year old. That said, she is on a mission to have the van painted to match Scooby Doo's Mystery Machine...

The dynamat wasn't so cheap, however I did get a good deal :-). It's a good product to work with, however butyl rubber and aluminum skin priced at this level is pretty hard for me to accept. I will say that it sticks like crazy, is odourless, and with some heat applied via a heat gun, is not coming off. It's basically two trunk kits. Rebuilding the AC system, I used a few square feet on the fans and speaker boxes as well: http://www.thesamba.com/vw/forum/viewtopic.php?t=2...;start=560

Not holding my breath, however the results should help folks decide if the expense is justified.

Sat Oct 27, 2012 9:07 pm

denwood wrote:
Not holding my breath, however the results should help folks decide if the expense is justified.

Thanks for doing this denwood. I'm looking forward to seeing your results. Well, actually, I'm looking forward to the "executive summary". You know, short attention span and all, those graphs look pretty but I trust your word. A "thumbs up" or "thumbs down" will work for me. :lol:

Sat Oct 27, 2012 10:10 pm

I'm really curious to find out the results of this test! I'm already sold on the idea of sound proofing. It's an upgrade that is within my range of capabilities! I pay retail for the other stuff...

Sat Oct 27, 2012 10:45 pm

I used fatmat in my bay and out made a huge difference. Those things are uninsulated tin cans though. Even with extensive sound deadening a stock vanagon is quieter.

Fatmat= similar product 100.00 for 100 cf. I think iy was 500 for comparable dynamat.

Sun Oct 28, 2012 11:30 am

Just finished testing. Any predictions?

Sun Oct 28, 2012 11:34 am

5% reduction in the back seat?

Sun Oct 28, 2012 12:15 pm

The primary purpose of Dynamat is to "deaden" the panels so they don't vibrate and act like a big speaker cone. The panels don't ring after application. You will need to add some kind of foam to stop noise transmission as you correctly call out with mattress down. If you look at new cars they don't cover every square in with Dynamat like material sometimes as little as 50%.

Sun Oct 28, 2012 12:23 pm

I agree the rear westy bed dampens the engine noise a lot, and that the wind noise in the front of the van certainly sounds louder than the engine noise...

I too am planning something similar to what you have done, with the addition of the repop "whistle stoppers" on the front doors.

The suspense is killing me.

Sun Oct 28, 2012 12:24 pm

Here are the results, in the same order as the first post, just AFTER Dynamat Extreme. I did confirm that both iPad and iPhone read very close to the same on a reference noise level. Note that the scale changes on the rear seat changes make the chart look a bit different. Compare based on the peaks (dashed lines) for each frequency. For reference:

Imperceptible Change 1dB
Barely Perceptible Change 3dB
Clearly Noticeable Change 5dB
About Twice as Loud 10dB
About Four Times as Loud 20dB

EDIT: Added the front seat results as an overlay comparison

front seat AFTER dynamat at 60km/h test 1

front seat AFTER dynamat at 60km/h test 2

front seat AFTER dynamat at 100km/h test 1

front seat AFTER dynamat at 100km/h test 2

rear seat AFTER dynamat at 60km/h test 1

rear seat AFTER dynamat at 60km/h test 2

rear seat AFTER dynamat at 100km/h test 1

rear seat AFTER dynamat at 100km/h test 2

Sun Oct 28, 2012 12:29 pm

So, was it actually quieter or not? Was the wind louder or the engine? I don't speak graph. :lol:

Sun Oct 28, 2012 12:58 pm

I would make these observations:

1. The Westy is louder in the front, particulary at lower frequencies! This has to be wind/road noise and is consistent with my observations that the engine on the highway at 100km/h is barely noticeable up front. I need to do one more test to get a better profile of the engine noise. I believe a lot of the noise in the rear seat is engine around the 2000 Hz level. Front seat before and after results are pretty much the same..no change.

2. Measuring your sound levels up front may always show poor results from sound deadening in the rear, regardless of what you've done due to the road and wind noise. So front seat passengers would not benefit from the treatment as I've done it.

3. Dynamat as I've applied it seems to be good for 3-5 db reduction in peak sound levels, but for rear passengers. EDIT: Note that the overall unweighted results in the back (numbers top left in the bar graphs) consistently show a 3-5 db drop using "flat" weighting on the RTA (real time analyzer). Stay tuned for an interpretation of this.

It would be fair to describe the difference to the lay person sitting in the back seat as "perceptible", likely at around 100hz. 100Hz is pretty low...you might describe a sound at 100hz as a low drone. Would I recommend applying Dynamat Extreme to a 90 Westy with stock sound deadening (on firewall) and the cushion in place?

Nope. If you were doing the entire vehicle, maybe. Cost there would be over $2000 easy.

There's a lot to read from these test as I didn't measure just peak sound levels, but rather peak sound levels from 20 to 20 000Hz!

Sun Oct 28, 2012 1:20 pm

thanks for your analysis

I cant yet understand how your tests start out at 80db and finish at 0db

I would be looking for a more consistent reading over time, more horizontal graph..

why do your readings drop to 0?

also, how do I put Faber Acoustical's Sigscape Pro on my iPhone? I cant find it in the appStore.

Sun Oct 28, 2012 1:51 pm

Jon_slider wrote:
I cant yet understand how your tests start out at 80db and finish at 0db

I would be looking for a more consistent reading over time, more horizontal graph..

why do your readings drop to 0?

The test doesn't really "start" at 80dB and end at 0, as this is not a graph over time. It's a peak (or average) across a frequency range.

Sun Oct 28, 2012 1:52 pm

Can you post the before & after on the same graph? I couldn't make sense of it with scrolling back & forth

Sun Oct 28, 2012 1:58 pm

front seat 100kmh test2 before dynamat

front seat 100kmh test2 after dynamat

I dont see the difference either