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1990 U1300L
10 Posts
Discussion Starter #1
My wife and I bought a 1990 U1300L ex-German military ambulance from George at last July. See pics below.

Our first big project was to sound deaden the cab. Here is what we did and the results…

As we went along taking stuff out and adding stuff in, we measured the Sound Pressure Level (SPL). We primarily used an iPhone running the "dB Meter Pro" app on an iPhone 6+ for the SPL measurements. The measurements should be viewed more as a relative reading from one change to the next. So, if we added something and the readings went from 70 to 68dB, that change decreased the noise by 2dB.

The absolute SPL measure on the iPhone was about 10dB lower than my old Radio Shack analog meter. That meter agreed within a couple of dB from a newer digital SPL meter my friend got from Amazon. So, add about 10dB to my measurements below if you want absolute SPL levels. I took all measurements with “A weighting”, dBA.

We also took the measurements over the same 1/2 mile stretch of highway near our home while traveling 90 kph. The bottom of the iPhone was pointed towards the windshield and held horizontally at about head level in between the driver and passenger for each measurement.

* Baseline - added 3M Crystal window film to all windows (7/31)
* 69-71dB Avg, 79dB Max, 79dB Pk

* Took out heater box, glove compartment, and metal dash top (8/6)
* 74dB Avg, 81dB Max, 79dB Pk

* Took out headliner, door panels, and wheel well’s thin synthetic leather covering (8/23)
* Added Damplifier Pro, FatMat, and Dynamat Pro to exposed dash area
* Added foam in depressions on rear wall
* Added Luxury Liner Pro on floor pan only (not center console bump up), on PS wheel well, not on DS wheel well, not on doghouse
* Note: dash still out
* 77-79dB Avg, 86dB Max, 85dB Pk

* Added Luxury Liner Pro on DS wheel well (8/30)
* Note: Luxury Liner Pro not on DS wheel well, not on doghouse
* Added scraps of Luxury Liner Pro within dash
* Note: dash still out
* 77-79dB Avg, 86dB Max, 85dB Pk

* Added Luxury Liner Pro (9/16)
* entire floor (not shifting platform)
* firewall (up to bottom of dash)
* doghouse sides
* not doghouse access door
* rear wall of cab except for DS window
* Added some of the Atkinson Vos Sound Deadening Kit
* entire floor (not shifting platform)
* doghouse
* firewall (up to bottom of dash)
* not dash pad
* not hood mat
* not roof mats
* Added Heat Wave Pro
* entire floor
* entire doghouse
* firewall (up to bottom of dash)
* Note: dash still out
* added scraps of Luxury Liner Pro within dash - not near fresh air vent
* Note: doors still naked - no sound deadening or door cards
* Added hatch headliner back in
* Added Damplifier to about 1/2 of roof
* Added heat shield to engine side of doghouse access panel
* heat shield made from Dynamat Hoodliner with thin Aluminum flashing on top
* Added Dynamat Hoodliner under factory heat shield on DS doghouse
* 71-73dB Avg, 82dB Max, 80dB Pk

* Added the rest of the Atkinson Vos Sound Deadening Kit (9/18)
* shifting platform
* dash pad temporarily installed
* hood mat installed (under hood reflective stick on mat)
* Note: no roof mats yet
* Added Heat Wave Pro
* shifting platform
* Note: Dash still out
* added scraps of Luxury Liner Pro within dash
* Note: doors still naked
* Added full roof Damplifier
* 66-68dB Avg, 77dB Max, 76dB Peak

* metal dash top piece in, AV sound deadening mat on top (10/?)
* heater hoses in place
* 67dB Avg, 76dB Max, 75dB Peak (10/23)

This is where we are now, 67dB average from a baseline average of 69-71dB. Despite the only 3dB of measured improvement, the noise is less harsh. We can carry on a conversation more easily. It still requires us to talk louder than we would in a quiet living room for instance.

Here is what we still need to do:
* Add in a dash panel where the original heater and glovebox were
* the glovebox area has a Vintage Air Gen IV Magnum heater/evap box now
* Attach a thick rubber sheet to the back of the cab at floor-level that goes horizontally to the front of the ambulance box
* the theory is that putting rubber spanning from the floor of the cab to the box will block some driveline, tranny, and exhaust noise from getting into the cab
* Upholste over everything
* Something on the “A” pillars?
* Add a "lead blanket” or similar to the injection pump?
* Any other ideas?

I will update the first post in this thread as we progress.

I am guessing we have added about 150-200 pounds of weight to the cab.

BTW, the ambulance box (with subframe?) will be up for sale soon since we are having a camper box built up for an around the world trip!

Thanks for reading!

2001 W163 ML270CDI / 2006 W164 ML500 / 1986 U1300L Unimog
189 Posts
I'm a graph nerd so love empirical data. Keep it coming! Last week I took my U1300L for its first highway run. It didn't have a dash, heater box, or the engine bay ducting for the blower installed. I could literally reach through the firewall and put my hand on the valve cover while driving. I expected to be completely deafened but I actually didn't think it was much worse than driving my suzuki sierra (Samurai in America) soft top on the highway. It was a freaking sauna though with it being 90F ambient temperature and the air from the engine bay (engine, rad, etc) blowing straight in through the gaping hole in the fire wall!!!

I'm not sure if you've had a search yet but there is a few good threads on sound deadening going into actual SPL reductions based on specific changes. It might streamline the process for you.
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