I rode in a 70's Mini once 1275 with a single box stainless center pipe that was remarkably quiet and found out that he had covered every hidden surface inside and completely underneath with rhino liner, it was and still is the quietest Mini i ever rode in even the doors shut with a thunk.

It's not too thick, but it definitely does dampen itWish I could explain it. A bare body panel tends to ring like an untuned drum. One with some dynamat on it seems to have more of a thud sound. A full coverage panel would be more of a muted and quicker thud. This stuff sounds like you're knocking on concrete. haha. near zero resonance, and it's quite in the car. We'll see how it all deals with a noise similar to this.

beautiful sounds

I thought about Lizard Skin , then KBS (like Por15), and a top coat over the lot. Slight worry about mils thickness. Think only the satin black KBS is needed.

Put black KBS on the underside of of the 911 and it's so hard it holds up great. Keeps moisture out also.

Thanks a lot to Dan and others for the great information on how to better insulate the car. At first, I only thought of doing the bonnet and maybe bulkhead, but will also consider doing the roof (as I need to replace the headliner).

Mtymous, please, keep us updated on your project, I would like to see how yo do it.

thanks to all,

Abel

Yeah, I can imagine that.  I own a Mini.

I'm interested, Mous.  I worried that Lizard Skin underneath might be too hard to do at the time, I just went straight to POR 15 and rubberized undercoat.  robably should have substituted Lizard Skin for the POR 15.

I support that whole heartedly. Anyone considering it should at least do the bulkhead. Heat shielding on the engine side of the firewall and sound deadening on the inside. If you don't want to do the whole firewall then at least do the bulkhead like Air said. You'll be surprised at the difference with such a small change.

If anyone is interested, I can keep giving updates on my build. I've decided to go with a layer of Lizard skin sound deadening under the entire car including the firewall and bulkhead then I covered all of that with Lizard Skin's ceramic heat coating. Then paint matched the whole lot.  The interior will have a bunch more done as well including full panel coverage on a few parts. Trying to make this car more enjoyable to drive daily and also trying to kill some of the nose from the gears I'll be buying.  The attached picture is my car as it sits now with the coatings already applied. 

It's aluminized heat barrier, there are a zillion different types and I can't recommend one over the other, got it at Summit.  I also cut it up for underneath the bonnet.

Is that silver material in your engine bay Dynamat?

Excellent comments from Dan and MtyMous.  Would add that - as we all know - 90% of our cabin noise is coming in through the binnacle opening.  With the gearshift and rear seat bulkhead a close second.

I've Dynamatted and shielded the firewall, adding dynamat only with the "knock method".  If the area of the panel resonates when you knock it, then put a little Dynamat on it - but only if it resonates.  Curved and compound-curved metal usually doesn't need it.   The door skins are of course notorious as is the roof.

In the photo you can see the little hole punched in where the plastic oil pressure feed line goes into the binnacle.  That's where I have the harness going in as well, and is the only opening.  Behind the reflective aluminum are a few layers of Home Depot "underlayment" plastic and foam that's used underneath wood flooring for noise.  And that hole for the harness is the only opening through it, so no more gigantic open hole.  Dynamat on the inside of the bulkhead as well.

Another surprising culprit is the rear seat bulkhead...That sucker vibrates like a timpani, and you wouldn't notice it until you knock it and deaden it.  Boominess gone from the interior.

Haha. That's true. A mini will never be as quiet as a Merc. 

Much of my knowledge is hard learned in multiple cars. The other chunk is from noise isolation and frequency shielding on large military aircraft platforms. Millions of dollars spent on that. Can you imagine flying for 30 hours with loud engine drone and sub mach wind noise? Fortunately it wasn't my money. I learned by proxy. Haha. But not surprisingly, the solutions still look very similar (barring very expensive advanced materials and honeycomb designs). 

I could tell you knew what you were talking about when you wrote "absorptive". I haven't seen anyone use that term out of industry. 

Thanks - my background is the technical side of building design, but the fundamentals are similar. Your comments are Mini-specific and from experience (and well-earned!) with them. Appreciated is your comment "And I've spent way too much money on other setups that didn't work."

I'd agree with your analysis of car floor treatment, adding that the carpet is huge in cabin internal absorption.

Re wanting "Mercedes-quiet"... I'd suggest buying the Mercedes.

Well said. I would maje some arguments for full coverage, but not to dampen vibration. Yes, damping of vibration and some resonant frequencies can be achieved with minimal coverage, but larger coverage works much better. There is a point of diminishing returns though. Each application has a different point where returns are lowered. If you want a mercedes quiet interior you will need a combination of sound killers.

First step is to use some sort of mass additive damping like lizard skin or dynamat. It will change the resonant characteristics of the panel. Then you need to insulate against the transmission through the panel which will require "blocking" that sound. You can do this much in the way I've done all of my cars with mass loading. I do this with a very thick solid vinyl mat. I heat form it to the floors and the firewall. 

If you want to take it one step further, you should add a cellular atructure between the resonance damping and the mass loading that can "catch" some other frequencies. Closed cell foam works best but is expensive. Especially if you get something made to deal with the floorboard environment. Moisture, etc. 

Look at any modern very quiet car and you will see a similar combination. Adhered to panels, then a carpet "pad", then a mass load, then carpet. Many of the new premium carpets out there have a thick vinyl mass load adhered to the carpet as a liquid and sound barrier. These will be either pre-molded or need to be steam molded to your particular floor as they are pretty hard to manipulate. 

I could go on for far too long about this stuff. And I've spent way too much money on other setups that didn't work. Let us know what you come up with. 

I haven't tried any of this, but the basic idea of acoustic treatment is that one needs to control transmitted sound and reflected sound.

Since no-one sits above the bonnet while driving (unless the windshield is missing), sound transmitted through the bonnet is insignificant. So, any treatment to the bonnet should be to reduce reflected sound inside the engine bay, which is what most bonnet/hood insulation does. For that you need an absorptive material. Look at factory hood insulation - it is typically lighter weight, fibrous material  with a thin, porous (to sound) covering. It allows sound to enter into the insulation where it is absorbed.

Firewall and floor acoustic tratment on the other hand is to reduce sound travelling through the separation. The obvious thing is to seal holes that allow sound to pass directly through. When sound hits a hard surface (steel in this case) the impulses are transmitted into the material, causing it to vibrate, and then re-generated on the other side. Sound 'deadening' material prevents the metal from vibrating. A good deadener has to subdue both intensity and frequencies. Too hard or solid a treatment will just vibrate at certain freqiencies. (That's why at 3:00 am you can hear your neighbour's bass but none of the rest of the "music'.) Generally it takes mass (thick but not too dense) to dampen transmitted sound.

A side issue is sympathetic vibration - this is where car roof and side panel acoustic treatment comes in. Take a Mini roof or door skin: realtively flat, smooth sheets of metal with little in them to stop them from absorbing sound (from any direction) and vibrating, causing their own "noise". Like a piano string or wine glass, one doesn't need to cover the whole thing to stop it from 'ringing'. A piano string damper is no more than an inch long and a wine glass can be silenced with the tip of a finger. That's why Minis were built with small strips of material stuck to the side panels. Okay, it is minimal and not successful against all sounds, but it isn't technically necessary to cover the whole panel to dampen them. What full coverage might do is, besides adding weight, help with absorbing sound within the cabin, if it is absorptive (see the bonnet notes above).

Another option is spray on.

I'm a fan of Lizardsin, you can do sound proofing and thermal coating together. They don't offer rattle cans though, it wouldn't be cost effective to do just the bonnet, unless there is someone in your area that would do just your bonnet. Doing above the head liner and the floor area can reduce/lower your interior heat level and lower noise in your car also.  

//www.lizardskin.com/

Apart from the precut kits available, what other options are there for insulating the bonnet/hood? I know that you have Dynamat/Fatmat but I was looking for something to stick on but with black instead of metallic side facing the engine. 

I am also tempted to use rubberized spray, but I don't think that would deaden much noise.

What do you guys use/recommend?

thanks,

Abel