Noise insulation - Dynamat

[waltsb2002]

Hello. I'm a new member to this group. Just found out about this site and the Yahoogroup, and have been perusing the wealth of information available.

We have a Silver with red front bumper 2002 EB E350 7.3PS diesel Quigley 4x4 with custom interior for surfboards, windsurfers, mountain bikes, motorcycles, climbing/kayaking gear, or just camping with the kids.

I have a few projects that I'd like input on, but I'll start with noise insulation. With the big diesel up front, and the cockpit sitting on top of the engine, we get a lot of interior engine noise. I just spent a bit of time, money, and effort installing Dynamat in the follwing areas:

1. double layer under doghouse
2. on underside of outer doghouse cover
3. double layer on floor under both seats
4. some spots under sonsole and undercarriage
5. all doors

Having done all this, I notice no decrease in engine noise! In fact, the perception is now that more noise, possibly higher pitched, is coming up higher through the dash than before. Although again, this is just a perception, as the doghouse and doors do seem more solid and transmit less vibrations than before.

Objectively, my Digital Sound-Level Meter recorded, before installation, an average of 75dB at idle, mid-80s while driving, and up to mid 90s under full acceleration.

After Dynamat installation, the readings have not changed.

I'm committed to fixing this, so that my wife and I can travel in relative peace and quiet (we still have the two kids, Isabella 4, and Hobbs 2...so I know true silence isn't possible), but any input and solutions would be greatly appreciated. We'll have plenty of time to meditate on the problem as we take off for the Colorado mountains next week!

Walt
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[jage]

Dynamatting my doghouse, although hardly as thorough, and my fridge changed my perception of the sounds (they are bassier) but I don't think mitigated the volume.

[waltsb2002]

I saw your pictures...mine was a similar installation on the doghouse. I think I need a stronger barrier around the firewall and up under the dash.

I'm wondering if the addition of a thicker sound-deadening foam under the doghouse and up under the dash would be helpful.

Walt

[Ford_6L_E350]

The only time I had severe engine noise was when the dealer improperly installed the doghouse.

It is fairly easy to get the doghouse gasket twisted or pinched and not have a good seal.

I had to install the doghouse and run a tool around it, under the gasket to get it into position. The difference in noise was tremendous. And the gasket wants to take a set and reinstall in the same bad position.

Without any added sound reduction, our PSD is quiet on the highway and only noisy when it is cold or when using a heavy throttle foot.

Mike

[scatter]

I'm with Mike. At least with the 6.0 we don't think it's a problem while on the road. Cold starts will wake the dead and hard acceleration will kick up the dB. Other then that, it's OK. I also increased the dog house and dash insulation without noticing any perceptable change.

[waltsb2002]

A good friend of mine has the 6.0 diesel, and they are noticeably quieter than its 7.3L predecessor. And I agree, when actually cruising on the road you notice the engine noise the least...it's not too bad.

Mike, I'll double check the gasket around the doghouse to make sure it isn't the culprit.

Thanks,

Walt

[kzemach]

Here's the answer I posted to you on the Yahoo group. Sorry, I should have checked here first for your post; I much prefer this medium for information exchange!

I did a two-step mod to address both heat and sound. I didn't check
dB levels, so it's a bit subjective. My approach was predicated on
the assumption that Dynamat-type materials are way better for heat
than noise; they're just too dense IMO to deal with noise the same way
dedicated soundproofing materials are.

Step 1: under dog house "insulation" with 1" thick FR grade neoprene
foam. I attached this foam to the inside of the doghouse with barge
cement, and then put several layers of metalized ducting material over
it to reflect heat. Had to cut away some of it where the turbo-tube
thingy comes close to the doghouse (and gets REALLY hot).

This seems to have greatly decreased the noise, as opined by both
myself and my partner. If I were to do it again, I'd do it
differently though; I'd do it more like the Badgers did and put stuff
under the stock fiberglass doghouse insert. Regardless of the fact
that I used FR grade foam, if it gets baked for a long time, a fire
hazard could still exist, so I have been quite careful about both the
installation thicknesses, locations, additional foil covering, and
occasional inspection. My point here is not for you to replicate,
but that a good sound absorbing foam, albeit much thicker than
dynamat, really seems to help on the noise.

Step 2: I used a dynamat-ish product (don't recall the name, but it's
a reputable one) and did a layer on the underside above the engine
toward the bumper... what I mean is, I took off the doghouse, and
slipped the adhesive sheets forward as far as I could get them, and
then stuck them up to that surface and to the sides. I then crawled
under the van and put more on the underside under both the driver and
passenger side to attempt to deal with road noise. I did some under
the carpets in the foot area and along the engine compartment sides
(thus there is one layer inside and one outside). After all this, I
noticed no noise difference, but a bit of heat difference.

Lastly, I did one door, but not the other, and noticed no noise
difference.

One thing I'd suggest doing is going underneath and closing up the
large hole on the drivers side that they cut to put in the water
connect and low water point drain. That hole was a major (HUGE, actually) source of noise in our van, and others have reported diesel fumes that came in most likely through that hole.

[lacoustics]

Walt,
I'm a new(ish) member too.. first post..but I've read the forum front to back over the last few months and found so much useful information. I am skeptical of the benefits of dynamat for the doghouse. Dynamat is advertised as a constrained layer damper...so it does not block sound as much as it helps reduce vibration in a panel that would otherwise radiate as sound. Dynamat should be very effective for large areas of sheetmetal like doors or a roof which radiated sound very well, but not so much for curved rigid plastic or composite parts which are not effective radiators.
What is known as 'mass law' in acoustics states that sound transmission loss is proportional to mass, where increasing mass decreases sound transmission. I see on dynamat's site that their standard product is .68 lb/sqft which is not that much. Heck, a 5/8" layer of drywall is approx 2 lb/sqft. Mass-loaded barriers are commercially available as noise barriers at 2 lb/sqft or more and would in theory block much more sound. Dynamat's extremeliner at 1.5 lb/sqft might work better but i'm not sure what kind of temperatures we need to account for or how much space there is to work with. Kinetics makes mass-loaded vinyl barriers that are used a lot in industrial applications, up to 2.5 lb/sqft.
I'd suggest going with the heaviest material you can find for the doghouse. I have a 7.3L and it seems that the majority of the noise comes straight through there..so treating any of the other paths of sound transmission would offer little to no improvement. Also in my van i've noticed leaks at the base of the doghouse, going to check how the gasket sits as Mike suggested.
The 7.3L is loud. For what its worth, OSHA requires hearing protection for people working full-time in environments over 90 dBA....

[Greg In Austin]

....but the Dynamatting is not all just for sound, even though that is what the product is marketed for, folks are also using it as insulation from heating ...

[Jeffrey]

I stuffed dense foam packing material into all the spaces behind the black snap-on cup holder part and also cut strips of 1/2" neoprene and filled the space between the doghouse and the dash going down the sides a bit. That made the interior quieter!