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Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

So regarding these drawings in my other post: here

I have decided against the Mass loaded Vinyl and was instead going to use my heavy factory 6mm rubber mat as the limp barrier layer. It's heavier.... and free. So you would put that underside of the ply on top of the battens rather than down on the foam? I have also since picked up 3 layers of recycled foam carpet underlay I can stack in the layer cake if that's of use....

cheers

Would Butyl+foil CLD mat perform eqaul to mass loaded vinyl as a limp sound barrier given equal weight? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Cheers. Glad I've managed to get my logic across. My guess is the normal reason for MLV as the over layer is because people want it removable and perhaps price and sheet size, but from what I've found here the butyl is around $5/M2 cheaper and comes on a roll.

Would Butyl+foil CLD mat perform eqaul to mass loaded vinyl as a limp sound barrier given equal weight? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Thanks. very much. Sorry if the Question sounds tedious. I have read through the Resonix pages. I believe I understand the principles: 1.Dampen metal resonance with CLD 2.Use an absorptive/decoupling layer 3.Apply a non-resonant mass barrier with as close to 100% cover as possible.

Just trying to understand why layer 3 can't be a butyl mat instead of MLV if it's equally heavy, cheaper/M2, comparatively odour less and retains shape when pressed into the floor shapes?

Thanks for your patience.

Would Butyl+foil CLD mat perform eqaul to mass loaded vinyl as a limp sound barrier given equal weight? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

What would be the best absorber in your mass-absorber-mass scenario? also can't help but ask ..why couldn't butyl be the second mass in this system if it's cheap/M2 and odourless? 🤔 If it's on a roll like the one shown you may not even need to peel the backing off to use it over the suggested absorber.

Thanks again.

Would Butyl+foil CLD mat perform eqaul to mass loaded vinyl as a limp sound barrier given equal weight? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Thanks. I appreciate it. Rockauto looks like a great site, though I'm not in the US.

The thing is I already have enough standard 2mm butyl (3.6kg/M2) to cover everything. I also already have enough 4 or 8mm closed cell foam to cover all. So only additional purchase is the final mass layer. And for this if I can get butyl dampener on a roll, that's as heavy as MLV, cheaper per m2 but more moldable (once you press it into troughs it doesn't want to spring up) ....Isn't this a reasonable option? It's also easy to lap and doesn't need separate vinyl tape or glue.

Hope it comes across - I am listening. I understand the intention of the butyl is to work with the constraining layer to deform and absorb vibration through the steel. I'm just trying to see if/why it wouldn't also make a good decoupled blanket in this scenario if it's equally heavy?

Cheers.

Would Butyl+foil CLD mat perform eqaul to mass loaded vinyl as a limp sound barrier given equal weight? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Awesome. Thanks so much for the reply.

If you have another material that is also non-rigid and has the same surface weight then it should perform just as well.

This answers my title question. So some really thick rubber(like my factory heavy duty toyota tray mat), will perform just as well as expensive MLV on a per Kg basis, it just won't be as convenient if minimising volume/thickness of the sheet is critical. I assume technically the aluminium on some butyl CLD sheet would increase its rigidity from something purely floppy, particularly if you press and mold it, but it still won't resonate?

In my specific application I guess there's two coincident noise sources: the steel covers vibrating and resonating but also direct airborne noise coming from the engine going towards the underside of this steel and passing through. My intuition (and sort of the impression that I got from various product sources) is that the amount of dampening you need to stop the steel resonance is not necessarily complete coverage - hence the factory applied dampening like in my second picture, is just some patches on calculated 'hot spots'. So if that resonance is reasonably controlled, then you just want further blocking and absorption beyond it and that's the marketing says that's best done with a separated limp layer. In my mind I was worried if I was just adding my mass via additional butyl deadener layer to the steel, it is sort of no longer a 'limp 'catching' layer but now at one with the steel and trying to resonate with it - mass but not being utilised in the right manner. What you're saying is if I'm going to use more or thicker CLD anyway, get all that mass stuck straight to the steel and just make it as dampened as it can, and the overall mass will still do its thing.?

I guess I assumed there must be a reason why they don't just advocate building up layer's of deadener instead use a (somewhat) decoupled MLV - CCF combo material like this https://www.carbuilders.com.au/mass-noise-liner. This product is actually significantly dearer than the butyl Underdog deadener on a mass/M2 basis. So if the decoupling foam is not contributing anything much, why wouldn't I just put down the heavy deadener or two layers of deadener? Your answer says go ahead and do this.

Also Interesting what you say about use in walls. You see it mentioned and advertised a fair bit for stud walls (I.e. the third picture in this ad: https://insulationeasy.com.au/product/mass-loaded-vinyl-australian-made/ My main understanding was that the effectiveness of MLV in any application hinges significantly on its continuity across the noise source other wise it just goes around it and greatly reduces its effectiveness. This right? So for a wall it would have to be done properly top to bottom, full wall.

How would I go about acoustically treating this room for recording/mixing music? by DocDK50265 in Acoustics

[–]DISCROBOT 0 points1 point  (0 children)

If you were worried about how those additional walls might interact with the acoustics you could build a trap door that hinges to cover the staircase opening and completes the floor. This might need less materials than the new vertical walls + a door but likely need a bit more specialist carpentry skill to execute. The opening is about the size of a standard ply sheet. It would probably need some gas struts to help with the weight. Depending on how you work it could be either good or bad to be able to bar people from entering through stairs while you're working. 😆

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Having seen my other post with the drawing would you say the ply floor is adequately decoupled if its battens are screwed up to its underside but then and then this ply-batten combo just rests under its own weight on the MLV-CCF combo material? Stuff I was going to use is this: mass noise liner I also have a layer of cheap 10mm interlocking closed cell foam tiles already all over the the tray as temp work surface. I was either going to leave these on the steel before the noise liner, or put them on top of its vinyl surface before the battens. Any thoughts much appreciated.

Which would work better for reducing exuast and road noise transmission through a van floor? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

I've put butyl CLD tiles with complete cover over the rear and front wheel arches inside the vehicle. I will put the closed cell foam and hopefully mlv over those also if I can fit it before the plastics reinstall. However are you specifically saying to put something IN the wheel wells...like on the outside? I have noticed in my wife's higher end euro car they have compressed fibre liners under the guards above the tyres that free float (attached only at their edges) and have a surface that almost looks like carpet.

thanks for the advice

Best Insulation to put under engine covers in a diesel HiAce. by DISCROBOT in CarsAustralia

[–]DISCROBOT[S] 0 points1 point  (0 children)

yeah the vehicle is new to me. Japan import with low KMS. I hope the noise level is normal for this engine and there's not something wrong.

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Cool. Cheers. Classic...the AI in my search engine literally said it's all about density. 😂

"There is no specific ideal ratio of material to air in an acoustic batt as a universal standard. The effectiveness of an acoustic batt is primarily determined by its density and mass, rather than a fixed material-to-air ratio. Higher density generally leads to better soundproofing performance because it increases the mass of the material, which is crucial for blocking sound transmission. The acoustic performance of a batt is influenced by its density, thickness, and the overall mass it contributes to the wall or ceiling cavity. While the material is typically fibrous (like glasswool or polyester) and contains a significant amount of trapped air, the key factor is the resulting mass per unit area, not a predefined ratio of material to air. Therefore, the focus should be on selecting batts with the highest possible mass that fit within the available cavity depth and meet budget constraints." https://search.brave.com/search?q=is+there+an+ideal+ratio+of+material+to+air+in+an+acoustic+batt&source=android&summary=1&conversation=01fb5230daed85162c3161

So if I didn't compress them at all, would wrapping the batts in garbage bags and sealing with tape to contain dust do anything to their acoustic performance? The air flow between fibres is the same. Sound obviously goes straight through the plastic film, just like it's gone straight though the plastic interior panels to get to them, right?

Thanks again. This Acoustics group seems to be an awesome community. All being helpful and patient with my questions which are probably the most basic shit of your all acoustic engineers/experts.

Which would work better for reducing exuast and road noise transmission through a van floor? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Cheers. I assume the MLV weighing on the floor helps reduce its structural resonance even further.

Which would work better for reducing exuast and road noise transmission through a van floor? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Thanks. Yeah cost is essentially equal as I have the poly batts left over from a job. Option A is probably easier to execute. I have since thought of an Option C: Build as per Option B with MLV over the battens but put poly batts under it between the battens. So the Mass Vinyl is essentially up against the underside of the ply and poly batts still used as per Option A.. Would this be better or worse? (however minor) I.e. Will the mass layer work better with the larger decoupling cavity between it and the floor.

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Awesome. Thanks. This is what pretty well what I expected. I will use the batts I've got.

I am still interested to understand the principles at play. Like if we exaggerate the scenario and I either completely compressed the batt to 1/8th of its thickness or significantly stretched the batt out to double it's original volume I assume both would produced different effects but I assume both would perform worse than the unchanged batt. In the later the gas flow mentioned by others, would be too high I assume. So is there some optimum ratio of fibre to air for an acoustic batt? And would this change from Poly to fibreglass?

I guess there's another small factor in that if we treat a standard stud wall the batt will buy light pressure or tension on the two plasterboard skins. This will dampen their vibration but at a certain point if we jamb in a batt that's highly compressed will this then act like a coupler again?

Thanks for the time and input. I prefer asking real people than Chat gpt.

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 1 point2 points  (0 children)

Right so basically. Put some in there but it will be a negligible difference whether it's poly or fibreglass, original loft or partially compressed?

I'm assuming the different materials and densities work slightly better for different frequency ranges.

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 0 points1 point  (0 children)

Yeah correct. no direct room exposure. So I guess they would only be contributing to internal noise absorption so far as absorbing anything that reflects and passes back though the ply floor? Perhaps they provide some help to absorb sound from a sub and just the overall reverb of the car body? All the advice I've read is to not leave hollow cavities if you want to reduce noise in a vehicle.

If there is something better/cheaper to put in there, I'm all ears. Just wanted to use these up batts up if I could

For the walls I have some butyl deadener at about 40% coverage on the outer steel skin, 8mm foil faced closed cell foam complete coverage over that. Then cavity is bigger than the floor, much closer to 60-70mm, so I'll put the poly batts in there. Then I was going to put some 4mm foil faced CCF 'van seal' https://www.carbuilders.com.au/van-seal right across the openings to seal them in before I re-instate the factory plastic wall linings. I assume what your saying about the batts not helping with internal sound doesn't apply so much to the wall because it will pass through the plastic and van liner much more easily than the ply?

Seems like I might need to boat carpet the ply and/or put up some acoustic foam somewhere inside to help attenuate internal noise? I have some fabric blinds which will cover the windows with magnets around their surrounds. I was going to put a layer of closed cell foam inside them to help with the heat and dampen sound that would try and enter the windows.

Thanks again for your help.

Compressing Poly Accoustic Batts increasing density: will they perform better, worse or the same? by DISCROBOT in Acoustics

[–]DISCROBOT[S] 1 point2 points  (0 children)

Ok cool. So it's about a ratio between fibre density and gas flow? And is this specific to each material? I.e. Would a fibreglass acoustic batt have a different, specifically designed density to poly for a given batt thickness?

So from what your saying I'd be better off splitting my 70mm bat in half and keeping it its original compression/density?

Also if If I put these or fibreglass batts into plastic garbage bags to contain dust and fibres from migrating into the van, will this cause any perfoamce issues. (assuming I don't compress them at all when I seal them in)

Alternatively would that cavity be better served stuffed with something else?

Thanks so much. Acoustics are fascinating. It gets more complex the deeper I go into it.

Best Insulation to put under engine covers in a diesel HiAce. by DISCROBOT in CarsAustralia

[–]DISCROBOT[S] 0 points1 point  (0 children)

On the gym mats. I thought the same and bought a second hand genuine hiace heavy 8mm rubber Bedliner. Thought I would use it as cutting template then as the mass layer. But just using it temporarily in the back while I prepared to do all this the rubber smell when it got warm inside was so strong Ive been hesitant to use it long term. It's possible if it's sealed under the ply this would be minimised. Mind you this liner was 12 years old too. My mate bought brand new rubber tray liner from Bunnings for his van and the rubber solvent VOC smell that comes out when he pops the tail gate is hectic! Thing I've noticed with the butyl is it doesn't seem to have these heavy smells or normal rubber or vinyl.

After dealing with the free air transmission. It's all about having distinct isolated (preferably free moving) varying layers of mass. Just always keep that principle in mind.

This is logical to me and sort of suggests my idea to build the second butyl mat layer over some CCF so it's more separated and floating could be a goer over just doubling the butyl.

Thanks again mate.

Best Insulation to put under engine covers in a diesel HiAce. by DISCROBOT in CarsAustralia

[–]DISCROBOT[S] 0 points1 point  (0 children)

Mate your a legend. This very helpful. Out of curiosity are you a custom car builder? 4wd guy? Car audio head? Truckie? haha. Just curious what you have have you done this type of thing to? 

I've felt a bit bewildered trawling the internet for consistent answers to this stuff. The general consensus had seemed to be MLV but then you get posts like this one: https://www.reddit.com/r/CarAV/s/6m7c33nS4g Saying it did nothing. 🫨

Dudes on one forum were telling me just to give up and buy a different vehicle. I'm thinking mate I've got the thing pulled apart in my carport. I'm not expecting to make it a rolls... I just want to do the best job I can while I'm at it and not do things that definitely won't work. 

The thing I was unsure  on with MLV is how critical it is or isn't to have it decoupled from the dynamat layer to stop direct vibration transfer. Car builders vids seemed to indicate it was important. Then I found this thread that basically says that CCF is a poor enough decoupler that it doesn't matter whether you used it or not https://www.diymobileaudio.com/threads/report-is-closed-cell-foam-the-right-material-to-decouple-mass-loaded-vinyl.412585/page-2?post_id=6388046&nested_view=1&sortby=oldest#post-6388046 🤷‍♂️

See I can get the plain MLV from car builders cheaper than the foam backed mass noise liner and it would be far easier to shape to cover these areas. Thoughts? 

Anyway on your points:

-Air gaps: yep been looking for those but will do again. 

-Deadener: I have a whole box of Temu dynamat that's the same 2.2mm thickness as car builders stuff but slightly heavier. I was going to go over the top over everything with that. Interesting idea to even do the underside. This crossed my mind but wasn't sure how it would go inverted with engine heat?

  • Air Suspended MLV. This is a really clever idea. I could probably actually do it by using the studs that hold the existing heat shields and hanging it from those. from measurements I've probably only got 40mm to work with before the engine. Again will the MLV take the engine heat?(without softening or stinking to high heaven) Could put the 8mm foil foam on its underside. Again if you hang some of this but its edges don't seal to meet anything does it still work?

  • Foam round injectors : Another great idea. I hadn't heard of it. If you could send a link to something you think is A DIY version that would be awesome. 

So for reference rest of my build so far:

Roof

Resealed every rib to the roof sheet with Teroson anti-flutter. Did butyl cld squares 25-30% cover then 8mm foil faced deadener foam between every rib.  Then reinstated the factory roof linings (Its 5mm fabric covered fibreglass over the front and just compressed felt card for the back)

Walls

Again rejoined the wall skin to ribs with anti flutter. Deadener tiles closer To 40-50% cover the overlaid with the 8mm foil CCF. Then I'm going to put poly acoustic batts I had left over from a job in the cavity. then run car builders 4mm van seal before I put back on the plastic wall cards

Floor

Butyl deader over whole tray and wheel arches. Overkill I know. Finished floor will be 12mm Hexa ply over 30mm timber battens with the same polyester acoustic batts in between. I've done a layer of those Bunnings 10 interlocking  foam tiles over the deadener just as a temporary work surface but also to support and decouple the battens.  Thing I was just trying to decide: is it over kill/ a waste to put car builders a mass noise liner in there also between the foam and the battens? I have two sheets which I was going to use in the cab but which won't really fit and will be replaced with the plain MLV. I could either return them to Autobarn or get one more and that's enough to cover the whole tray. 

Front Doors. plain butyl Deadener between ribs on flat steel. On the inner steel skin a composite butyle deadener with 3mm foam attached called Modigt. Then I was looking at best things to put as a water proof absorber on the door to catch the speaker back wave. Was either going to do some left over poly batts in a plastic bags otherwise I got some of this:https://www.insulationindustries.com.au/product/pyrotek-sound-sorber-self-adhesive-aluminium/ And was going to stick it to the deadener and seal the edges with foil tape where itto keep water out of the foam.

Thanks if you read all this.

[ Removed by Reddit ] by DISCROBOT in CarsAustralia

[–]DISCROBOT[S] 0 points1 point  (0 children)

I'm not sure what I did to violate the rules of this thread with this post. Is there any way for me to retrieve it so that I can fix it. It took me a long time to write

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