[blau3er]

Following on from my recent Bang & Olufsen retrofit (which can be found here: https://f30.bimmerpost.com/forums/sh....php?t=2035057) - I decided that the next logical step would be to add some sound deadening to the car to further improve things.

I ordered up the materials from Dodo Mat here in the UK, and got to work...



The products I bought was their 2mm Deadn Pro, which is a butyl / aluminium deadening mat and I also bought their new SQ acoustic liner, which is a closed cell foam.

The first job I tackled was adding in deadening into the sub enclosures, pretty easy and the material was thin enough to sit under the plastic ribs of the enclosure, meaning there is no risk of interference.



Next up was a systematic approach to the doors.

I added butyl deadening and foam to the reverse of each door card, which added some substantial mass to the door cards. I replaced all of the door clips and added Tesa tape to the mounting locations to eliminate any rattles.

Front door card:





Rear door card:





Next, with the help of Wibbles we got the front seats out, so that I could add some deadening underneath the sub woofer enclosures. Again, the material was thin enough at 2mm to ensure that no interference issues were caused. Whilst there, I also added deadening into the B pillar area, but I forgot to take a picture of that!



I then moved onto the sheet metal of the doors. I firstly added deadening to the inner door skins, where possible. However, I focussed mainly on the reverse side of the outer door skin, adding in a substantial amount of deadening and covering that further with the acoustic foam.

Front door:











Rear door:











The vapour barriers had taken a bit of a beating from fitting the new tweeter wiring, so to satisfy my OCD, I opted to take the opportunity of replacing all 4 and re-fitting them with all new genuine BMW butyl rope. Expensive, but worth it for peace of mind and dry carpets!

Note, the rope is one continuous piece, the cuts in the pictures are just relief cuts that I made to the backing paper to stop the rope from twisting when laying it on the new barriers.



END RESULTS....

100% worth the effort, rattles have disappeared from the doors and the sound quality is even further improved. In fact, I have had to turn the bass down now, as its much more present and powerful as a result of the deadening. Clarity is also further improved, especially vocals and highs.

I did this in small 2-3 hour chunks over several days - and I'm really glad I made the effort!

[MEN54]

Nice! I like these types of projects

[Billfitz]

Low frequency noise is the main problem. Low frequency noise is best controlled with the application of high mass butyl. Foam is used inside everything from speaker enclosures to recording studios to reduce midrange and high frequency reflections. It has no effect on low frequencies, so put butyl anywhere and everywhere that you can, and don't bother with foam. For instance, when I opened up my doors to install real crossovers on the midranges and tweeters I fully lined them with butyl, not only on the exposed sheet metal, but on the original foam barriers as well. Every time I've pulled off interior trim to do one thing or another I lined it with butyl. All in all I've realized a 9dB reduction in the low frequency noise floor. To put that in perspective it's the equivalent of increasing the underseat woofer power from 50 watts to 400.

[NealfromNZ]

It’s certainly worth doing and does make a difference. With the underseat woofers my replacements also came with a high density foam gasket/ spacer. That also helped reduce rocker pannel buzz compared with factory woofers that use some kind of silicon gasket.

Rear trunk / boot lid and number plate mount was also one of the worst areas of rattles / resonance. Not sure if the rear tail gate did the same in the F31 ?

[blau3er]

Originally Posted by Billfitz

Low frequency noise is the main problem. Low frequency noise is best controlled with the application of high mass butyl. Foam is used inside everything from speaker enclosures to recording studios to reduce midrange and high frequency reflections. It has no effect on low frequencies, so put butyl anywhere and everywhere that you can, and don't bother with foam. For instance, when I opened up my doors to install real crossovers on the midranges and tweeters I fully lined them with butyl, not only on the exposed sheet metal, but on the original foam barriers as well. Every time I've pulled off interior trim to do one thing or another I lined it with butyl. All in all I've realized a 9dB reduction in the low frequency noise floor. To put that in perspective it's the equivalent of increasing the underseat woofer power from 50 watts to 400.

The foam was recommended to me by Dodo and others, its clear you have lots of audio knowledge - but this is a subject I don't really know much about! Only my ears to rely on to tell if there is a difference.

I would be interested to see if you have any pictures of the butyl sheets on your existing foam vapour barriers - I would be keen to add some there, as it strikes me as a weak spot in terms of noise. However the weight and thickness of my butyl sheets would probably damage the OEM barrier, and I really don't want leaks!

9dB reduction sounds very impressive! Have you had your floor carpets up and added deadening under there? Thats maybe a job for the future for me. Next, I want to tackle the rear quarters, as externally when you tap them they sound like a tin can! I will also get the boot area done too.

Originally Posted by NealfromNZ

It’s certainly worth doing and does make a difference. With the underseat woofers my replacements also came with a high density foam gasket/ spacer. That also helped reduce rocker pannel buzz compared with factory woofers that use some kind of silicon gasket.

Rear trunk / boot lid and number plate mount was also one of the worst areas of rattles / resonance. Not sure if the rear tail gate did the same in the F31 ?

F31 externally seems to really rattle at the side skirts - I think they would need to come off and have some foam applied to tighten up the fitment. If you press on them with a finger, the rattle stops!

Originally Posted by MEN54

Nice! I like these types of projects

Thanks, its been quite an enjoyable project so far!

[Billfitz]

Originally Posted by blau3er

The foam was recommended to me by Dodo and others, its clear you have lots of audio knowledge - but this is a subject I don't really know much about! Only my ears to rely on to tell if there is a difference.

Lots of places recommend buying their products whether appropriate or not.
Foam, polyester fiber, fiberglass batts, butyl and other materials are all referred to in the trade as damping materials. Porous materials damp midrange and high frequency reflections, solid materials damp physical vibrations. The source of most road noise in cars is physical vibration, so the fix is solid damping. To the extent that midrange and high frequency reflections in the cabin need to be suppressed that's accomplished by the carpets, roof liner, seats and water bags, the 'water bags' being you and your passengers.

I would be interested to see if you have any pictures of the butyl sheets on your existing foam vapour barriers -

Sorry, I didn't take any. I used large enough sheets to span across the foam, attaching to the surrounding metal, not the sheets themselves.

9dB reduction sounds very impressive! Have you had your floor carpets up and added deadening under there?

I thought about it but the felt carpet underlay in my F34 is very thick, so between that and the carpet there's enough mass to keep the floor vibration to a minimum. From what I've seen other F models may not have as thick an underlay.

F31 externally seems to really rattle at the side skirts - I think they would need to come off and have some foam applied to tighten up the fitment. If you press on them with a finger, the rattle stops!

The skirt vibrations are excited by the underseat woofers, which vent into chambers under the floor. Mine don't bother me, I can't hear what they're doing inside the car. If they did bother me I'd pull them, line them with butyl, along with whatever is behind them, and secure them better using double sided tape. I wouldn't use foam, as that would hold moisture, which could eventually lead to rust where it contacts metal.

[kovalchuk71]

Originally Posted by Billfitz

Low frequency noise is the main problem. Low frequency noise is best controlled with the application of high mass butyl. Foam is used inside everything from speaker enclosures to recording studios to reduce midrange and high frequency reflections. It has no effect on low frequencies, so put butyl anywhere and everywhere that you can, and don't bother with foam. For instance, when I opened up my doors to install real crossovers on the midranges and tweeters I fully lined them with butyl, not only on the exposed sheet metal, but on the original foam barriers as well. Every time I've pulled off interior trim to do one thing or another I lined it with butyl. All in all I've realized a 9dB reduction in the low frequency noise floor. To put that in perspective it's the equivalent of increasing the underseat woofer power from 50 watts to 400.

Any suggestions on a decent high-mass butyl product distributor? Not interested in retail products with "flashy" names that are marked up 200%.

[Billfitz]

I use 80 mil butyl. Amazon is as good a place as any to get it from. I agree on staying away from over-hyped over-priced name brands. Butyl is butyl. One recommendation: https://www.amazon.com/Kilmat-Deaden...0751CBXBT&th=1

[mrpingu]

What’s the best place to start with sound deadening for road noise and in which order of effectiveness.

- outer metal inside the doors?
- inside on the metal of the doors, like shown in the pictures right from the midrange speaker?
- inside wheel liner?


Is this any good?
https://www.biltema.no/en-no/car---m...pcs-2000044169

[Billfitz]

The problem with the outer metal inside the doors is that when they get hot sitting in the sun the adhesive can fail, so they may end up sitting in the bottom of the doors. As I noted I put mine over the inside sheet metal of the doors. Inside the fender liners wouldn't hurt. If your carpet liners aren't at least 12mm thick lining the floor would help. The linked material is 78 mils thick, which is good. The aluminum doesn't do anything, butyl without it will work just as well, but it seems that everyone uses aluminum. That's because people would be inclined to use aluminum layered rather than plain because they don't know any better.

[mrpingu]

Originally Posted by Billfitz

The problem with the outer metal inside the doors is that when they get hot sitting in the sun the adhesive can fail, so they may end up sitting in the bottom of the doors. As I noted I put mine over the inside sheet metal of the doors. Inside the fender liners wouldn't hurt. If your carpet liners aren't at least 12mm thick lining the floor would help. The linked material is 78 mils thick, which is good. The aluminum doesn't do anything, butyl without it will work just as well, but it seems that everyone uses aluminum. That's because people would be inclined to use aluminum layered rather than plain because they don't know any better.

Thanks for insightful response. Good to know that quality is OK, it’s the cheapest available locally.

Is it really a thing that these end up in the bottom of the door if on outer metal? I live in Scandinavia so ambient temperature is almost never above 25 degrees, I do however have a black car…

Floor carpet is quite think I would say, I don’t think I will bother pulling the carpet.

[Billfitz]

I added it to the rear package shelves. Even though they're inside the car it got hot enough for them to fall off, so I had to add screws to secure them. The sheet metal of a car gets very hot when in the sun, irrespective of the ambient temperature.

[mrpingu]

Originally Posted by Billfitz

I added it to the rear package shelves. Even though they're inside the car it got hot enough for them to fall off, so I had to add screws to secure them. The sheet metal of a car gets very hot when in the sun, irrespective of the ambient temperature.

Can I use your knowledge once again?
2 question, I didn’t do the inside of the door cards, I have to open up the doors again soon. Would adding to door cards itself also help?

I came across this: https://www.biltema.no/en-no/car---mc/workshop-equipment/lifting-equipment/car-jacks/noise-insulation-board-bitumen-500-x-1000-mm-2000021213

It’s only 1.2mm but it’s very cheap. Much cheaper than the other one I linked before. For example I could do the trunk floor with this?

[Billfitz]

If you've got it on the doors there's not much, if anything, to be gained adding more to the cards. Too much and they might not fit in place again. Also, BMW door cards are very substantial, twice the thickness and weight of most cars. If they were Toyota thin I'd line them.
1.2mm is only 50 mils, but if it's cheap enough you could use two layers.

[mrpingu]

Originally Posted by Billfitz

If you've got it on the doors there's not much, if anything, to be gained adding more to the cards. Too much and they might not fit in place again. Also, BMW door cards are very substantial, twice the thickness and weight of most cars. If they were Toyota thin I'd line them.
1.2mm is only 50 mils, but if it's cheap enough you could use two layers.

I see.

Roughly 14 dollar per square meter vs 40 per square meter.
Accounting for thickness and do double. It’s 28 vs 40 per square meter

[NealfromNZ]

Have a look at the results in this testing. A similar 50mls product dropped sound level by less than 5db. Personally wouldn’t bother.

Also watch some bitumen products from a smell prospective.

On the other hand see if stinger products are available where you are. Very effect product for the price.

https://resonixsoundsolutions.com/be...-testing-data/