Sound proofing old work Hiace van

My latest Hiace is a basic '01 non-turbo model but it's rather noisy on the road. Sustained speeds above 90km need ear plugs! The sounds include what appears to be engine fan noise. There's no sound deadening behind the inner panels in the cargo area and the floor is nicely covered with simple plywood. I guess it sorta echoes like a tin box.

Anyone got any good ideas to improve sound/noise.? Probably will add carpeting..

Thanks!

Carefully taking note yesterday, I think some of the excess noise comes from induction roar, tyre noise on road and radiator fan howl.

The rear wheel arches are bare steel so they could have some sort of covering.
The side panels are very thin and behind them it's hollow. Whatever I put in there need to be water/damp resistant.
Floor covering is the standard plastic with integral thin underlay.

Yes that's a real recipe for a lot of noise. Go to some of the car stereo installation places (MAD Soundz, RPM car audio, etc) and get them to show you what they use, there are many products they have access to which you likely haven't seen or heard of. Jaycar (there's that name again, sorry) have a very limited selection there too.

Yes. I see the stuff I need, stick-on butyl rubber sheet. Looks like it forms to most any contour. I recall seeing it plenty of times in cars. Seen a demo on Youtube where a small piece was placed on a big brass musical symbol, it cut the sound off dead. Amazing.

It's quite pricey especially when considering how much I need. Some hundreds of dollars worth. Will bide my time, wait it out and see what turns up. Meantime, I know someone re-carpeting...

Hello.

Yes, there are lots of people who make this stuff. Dynamat is probably the market leader, but very expensive. All of them work the same way and do the same thing by adding mass to the panel to change its resonance and deaden vibration.

This stuff will only do these two things. It won’t reduce vibration transmitted through solid parts such as road noise into sub frames into the vehicle chassis. To counter this is much harder. It also won’t reduce sound transmitted in other ways, but if the sound or vibration tries to reach the observer through the skin of the vehicle then it will work.

If you are contemplating doing this (as am I) then it seems to be important to recognise where this will work (big flat areas) and where it will not (curved areas or where the panel is bent to strengthen it). Basically if you can tap the panel and it boings then it’ll work. If the panel is already acoustically dead then it’ll be less effective. The point here is not to try to cover the entirety of the van as you’ll be adding mass for no benefit and it won’t deaden other sounds.

There are lots of YT videos so it’s probably worth doing more research, especially in trying to deaden the harder to quieten areas. Thick floor matting etc will help here, just as carpets and curtains better quieten the resonance in a room, rather than hard furnishings.

The other things to consider is whether to add thermal insulation at the same time and improve the vapour barrier(s), which are rather poor; these are especially important if you intend to use the van as a camper.

Interested to know what you end up doing.

HTH

Here's my blank canvas at the moment. I've got all the camper fittings out ahead of work underneath, various rust-proofing, changes to wiring, improved sound deadenning and insulation. Simples!

Thanks, am learning heaps.

Today I recorded decibel readings from a Galaxy app.

50kph = 81db
80kph = 85db
100kph = 85db

Surprisingly there was no difference between 80 & 100kph figures.

Is that because it maxed out your measuring device?

Somewhere in this link is my solution:

https://hiace-super-custom.forumotion.com/t3479-camping-conversions

I basically bought 5mm house flooring insulation sheets.
Cut strips to fill the gaps / strips in the floor.
Then 2 (or 3 - I have conduit for cables going from left to right) layers on top.
Then 10mm marine ply.
Then some spare hessian backed carpet.

The decibel meter seems to be working as expected. It has a dial up to 100db. Will verify when I get the grinder out next..

House floor insulation sheet seems like something I should hunt out., thanks. My '01 shorty already has ply installed.

Studying the sound some more, I think some is coming from induction roar beside the driver right ear. This would be a good place for some noise-deadening treatment.

Made some good progress.

Some layers of carpet in the back and under the drivers seat etc made a noticeable improvement.

Bought some stick on foam rubber. Used some in the intake duct area. Another 8 sheets of foam to stick on wherever looks good. Shortly I'll pop the side panels...

Around this time, I discovered the air intake hose was split. Replacing it may have helped reduce induction noise volume.

Quite a lot of noise comes from up front, over 80- 90kph. Sounds like fan noise or perhaps air/wind howl. Yet to isolate cause but is speed related.

About time I retested the DB noise meter...

The front sunroof seal can make a lot of noise!!

Yes, agreed about sunroof noise though my van doesn't have one. This sound could easily be wind whistling over the surfaces or edges.
Next I'll try driving at 100km, then suddenly dropping out of gear so engine comes back to idle. In this way I might be able to determine if it's fan or wind noise.

Latest DB readings with notes:

50kph = 76db (down 5)
80kph = 83db (down 2)
100kph = 83db (down 2)

Discovered DB meter varied depending on where it was placed. By the steering wheel it was a couple points less than by gearstick.
Also road surface had quite an impression on figures.