Live Sound & Production

[Audiopile]

In my personal quest to see just how much crow I can eat in a lifetime, I'm the new owner of well used but seemingly expensive (to my standards) Sprinter van... after my badmouthing them for years as being seemingly expensive to repair and a little to "tinny" and over-engineered for my tastes.

Anyhoo... (cough... got a little of that crow stuck about 1/2 way down)... After a few intense days of flogging along, I have most of the really obnoxious squeaks, rattles, and clattering tamed down to the point where the rattling and booming of the bulkhead has my attention.

Does anybody have any thoughts or seen some good ideas on taming the noise inherient in a steel bulkhead?  I'm thinking of covering one side... possibly the cargo bay side... with 3/4" neoprene foam.

[dboomer]

We used to use spray-on undercoating in the old days ...  but it adds weight.

[RoadRanger]

Butyl rubber flashing tape:

http://www.homedepot.com/p/Quick-Roof-EPDM-Self-Adhesive-Rubber-Flashing-Tape-FT910/202267106#.UUNUa...

A few strips dampens the panel

[Audiopile]

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dboomer wrote:

but it adds weight.

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That was my concern with adding neoprene foam... it will add weight... and might not really reduce the booming of the bulkhead, and might prove to be an exercise in futility... like putting heavier heads on a drum to try and make the drum quieter.

Maybe sheeting it in plywood... even thin plywood like 3/8" might actually work better by stiffening the bulkhead so it isn't so boomy.

I guess if I filled the cargobay with something to hold the bulkhead from flexing... that might work.  I wonder how many cans of foam it would take to fill the cargo area of a Sprinter van?

[RoadRanger]

Did you miss my post? That is what we used in products with sheet metal cases.

[Audiopile]

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RoadRanger wrote:

Did you miss my post? That is what we used in products with sheet metal cases.

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Well... yes & no.  I saw your post after I posted my reply to Don.

I researched the rubber roofing stuff (not available at our local Home Depot... but it looks like I can order it on-line)... it looks like that could be handy stuff to have around.  Do you just stick it on, or do you stretch it to maybe add some pre-load type rigidity to the metal panels?

[RoadRanger]

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Audiopile wrote:

I researched the rubber roofing stuff (not available at our local Home Depot... but it looks like I can order it on-line)... it looks like that could be handy stuff to have around.  Do you just stick it on, or do you stretch it to maybe add some pre-load type rigidity to the metal panels?

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Just stick it on. It doesn't add any rigidity but takes the "ring" out of sheet metal panels by dampening them. You don't need to completely cover the panels. An automotive supply house might stock something as good or better...

[dboomer]

So what works is limp mass ... the more mass the better. Alas, more mass, more weight.   Sheet lead would be great

Seems to me I remember a lead lined material the car audio guys use.  All this too ...  http://www.parts-express.com/cat/sound-damping/409

[RoadRanger]

^ Yup. I suppose a dozen layers of latex paint would help too, just keep adding a layer every few days until "done"  .

[Telecruiser]

www.silentcoating.com

[Crownman]

Throw some Dynamat in there.  We did the inside of a buddies van and it worked great.

[Bugzie]

Foam backed carpet. Thats basically what comes on the new ones and it works well. Why are you worried about such a small amount of weight? Those things are incredibly efficient as far as mileage goes.

[Audiopile]

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Bugzie wrote:

Foam backed carpet. Thats basically what comes on the new ones and it works well. Why are you worried about such a small amount of weight? Those things are incredibly efficient as far as mileage goes.

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I'm not concerned about adding some weight... unless I'm just adding weight but not actually solving the problem.

I've noticed that if I have cargo against the bulkhead, the bulkhead noise is virtually entirely eliminated (reduced by 99.9%+).  I envision that adding more vehicles to the Tacoma Narrows bridge (Gallopin Gertie) likely wouldn't have eliminated the oscillations that destroyed the bridge:

http://www.youtube.com/watch?v=j-zczJXSxnw

But, as I understand it, a well placed shock line (maybe as small as 3/8" and weighing pounds, not tons) if added to the bridge may have nipped the oscillations in the bud before they had a chance to start.

My vehicle's bulkhead oscillates... fairly severely under some conditions... and makes a lot of noise doing so.  Diminishing or eliminating the oscillations and thus eliminating the noise is the objective.  The weight of the method of resolution is a minor consideration.

[agedhorse]

Gluedown Ozite speaker carpet (not the cheap Chinese stuff) on both sides will minimize the radiating effect (and make it look cleaner)

Possible add in a shallow bow truss with threaded rod, a turnbuckle and rubber bearing block would take care of it as well.

[TimmyP]

Make a cardboard templace of the shape of the panel.  Use that as a pattern to cut a batten out of good plywood, scrap maple, etc.  (min 1" height).  Glue the batten to the panel with silicone, etc. (press firmly into place with sticks until dry).

[Audiopile]

Thanks to all for the suggestions.

I have discovered that simply tightening the myriad of bulkhead fasteners diminished the bulkhead noise to a fairly negligible level.  There's still some panel flex which I'm addressing with an application of 1/2" plywood riveted to the panels over 3/8" neoprene foam.  I'm fixing on finishing that project this weekend.

I've discovered a flaw in my Sprintervan noise reduction project... being:  The first thing one of my employees noticed and pointed out to me after I'd eliminated most (90%+) of the cabin noise was the fact that the radio didn't work... the fact that the noisebox didn't work wasn't an issue before the noise reduction campaign.

[RoadRanger]

^ That'll teach yah!