[DerAlte]

Originally Posted by schakravarthy

... From what I have gathered, these might need additional foam reinforcements to achieve good results. ...

Incorrect. 'like jack of all trades' is a rather amusing, even though unjustified, inference.

The commercial damping materials are sufficient to damp out a wide range of frequencies - which is what one faces in actual driving. Foam, on the other hand, will only damp out higher frequencies - faithfully passing through low frequency rumble. To diminish panel resonance, car manufacturers use strategically placed high density materials like mica-stabilized tar felt or butyl rubber based material containing tar and mica.

Originally Posted by schakravarthy

... I'm trying to emulate the layers found in the commercial dampeners, but with alternative materials. ...

Please do compare the density of the commercial damping sheets with the alternative materials.

BTW, by "layers found in the commercial dampeners" which dampeners / area of application were you referring to? The material is never the same in all applications.

Originally Posted by schakravarthy

... I didn't understand what you meant by "limited access". ...

As soon as you open the door pad, you will realize the problem in accessing the outer layer/panel of the door (there are plenty of pictures in the "Sound Off and Show Off" thread). That is where most of the damping should be applied, apart from the door pad itself (large areas not interrupted by stiffeners or folds, since these are the areas that resonate and/or transmit the induced noise). And accessing that will require some contortion since the window winder and other odds & ends come in the way. Which is why professionals, for whom time is money, prefer the simple preapplied-adhesive-on-one-side damping sheets - whose effectiveness in automotive applications is not in doubt.

[sajjt]

Originally Posted by DerAlte

The commercial damping materials are sufficient to damp out a wide range of frequencies - which is what one faces in actual driving. Foam, on the other hand, will only damp out higher frequencies - faithfully passing through low frequency rumble. To diminish panel resonance, car manufacturers use strategically placed high density materials like mica-stabilized tar felt or butyl rubber based material containing tar and mica.

Sir, how about the self adhesive cork + tar felt sheet, the one we used to apply on the sheet roofings for leak proofing? Will that be better a replacement than the yoga mats or the PU foam sheets? What do you say?

[DerAlte]

Originally Posted by sajjt

Sir, how about the self adhesive cork + tar felt sheet, the one we used to apply on the sheet roofings for leak proofing? Will that be better a replacement than the yoga mats or the PU foam sheets? What do you say?

If you can get some, yes, it would work. 2 small problems though:
* In hot weather, there is a possibility that some of the volatile chemicals in tar will slowly evaporate and you will have to bear the smell. Since it is meant for outdoor application, one doesn't feel it otherwise
* Unless the tar is stabilized by mica (most good sheets are) there will be a tendency of the tar to 'run' in hot weather

[sajjt]

Originally Posted by DerAlte

If you can get some, yes, it would work. 2 small problems though:
* In hot weather, there is a possibility that some of the volatile chemicals in tar will slowly evaporate and you will have to bear the smell. Since it is meant for outdoor application, one doesn't feel it otherwise
* Unless the tar is stabilized by mica (most good sheets are) there will be a tendency of the tar to 'run' in hot weather

Its easy to source, almost all hardware /sheet vending shops have this.

I guess the smell will be evaporated fully within a few days seasoning in a open parking slot I have closely observed that once its fixed properly it will stick for long even its being exposed to extreme weather conditions and never saw this bleeding due to sun burn.

I am leaning towards it mainly two reasons:

1. Ease of applying as its self adhesive and very flexible like commercial ones with enough thickness.

2. cost effectiveness, it wont make a hold on my pocket even if I apply all over the car

[schakravarthy]

DerAlte, at the cost of sounding woefully stupid, let me sketch out what I intend to do.

• Add a few bits of neoprene rubber (mass damping) to the outermost panel of the door. These when strategically placed, I believe, will reduce the vibration of the door by altering the resonance frequency.
• Next, a layer of neoprene rubber sheet will be used to cover the bare metal parts of the door. This will again act as a mass damper and cut down the vibrations of the door metal.
• Next will be a layer of the gray closed-cell foam (the kind commonly used in packaging) which I will stick to the rubber layer. This part will act as the sound absorber.
• Another layer of a different foam material will be stuck to the gray closed cell foam layer. This layer too will act as a sound absorbing layer and will further filter the noise.

All the above layers will be on the metal part of the door. Each sheet will be no more than 2-3mm in thickness. I have ascertained that the door can take in this thickness without any hindrance.

• Next, I will wrap the inner portion of the plastic panel of the door with neoprene rubber. The rubber will be cut to the contours of the panel and will serve as a mass damper as well as a sound barrier.
• If there's space still left, I will use a thin layer of foam as an additional barrier over the previous layer.

The same process will be iterated on the boot door and spare wheel well.
For the firewall, I'll go the conventional commercial damper way as I don't trust the foam so close to a heat zone.

PS- The reason why I dubbed the commercially available products as 'jack of all trades' is that one will, invariably, have to use (and pay!) for all the three layers, viz., mass damper, sound absorber and a sound barrier, irrespective of whether one needs the three layers in his application or not! These products offer a one-fix solution, whatever your need be.

I apologize if you found the statement unwarranted/unjustified. Though I'm not a fan of these products, I too would have gladly embraced the off-the-shelf way, if only it didn't require me to part with so many Gandhijis.

[::CMS::]

Originally Posted by DerAlte

If you can get some, yes, it would work. 2 small problems though:
* In hot weather, there is a possibility that some of the volatile chemicals in tar will slowly evaporate and you will have to bear the smell. Since it is meant for outdoor application, one doesn't feel it otherwise
* Unless the tar is stabilized by mica (most good sheets are) there will be a tendency of the tar to 'run' in hot weather

I tend to disagree. I was also having doubt about the issues of smell and melting in direct sunlight. I had applied 3 layers on the outer panel, 1 on the inner panel side1 and 2 layers on the side2 (altogether 6 layers per door) for both the front doors in my Duster. The smell was there for just 1 or 2 days since I had used fevicol SR to stick the layers and I checked the durability by parking it in the direct sunlight for 5-6 hours for several days and I never had any smell or any other issues. I blindly recommend the Bitumen sheets used for waterproofing to damp the doors, bought 20mts roll (more than enough to cover an entire car) for just ~1200/-

[DerAlte]

Originally Posted by schakravarthy

... let me sketch out what I intend to do. ... I don't trust the foam so close to a heat zone. ...

... one will, invariably, have to use (and pay!) for all the three layers, viz., mass damper, sound absorber and a sound barrier ...

I don't think I have the teaching abilities to make you understand. Let me mention a couple of small points hoping it will provoke questions in your mind regarding your 'theory':
* Butyl rubber / neoprene is not the 'mass damper'. Rather, it only provides a binding structure for the materials that provide mass
* By itself, the rubber is (mechanically) the equivalent of a spring, so it cannot be a 'damper' by itself. For example, a 'shock absorber' on a bike is a combination of a spring and a damper. The spring is required since the damper, after absorbing energy, cannot go back to it's original position otherwise. To know what happens when the damper isn't present, just ride in the last seat of a state transport bus which don't have dampers any more
* *ANY* material, even styrofoam, open/closed-cell foam or paper/cardboard, pasted on to a metal sheet will reduce some vibrations. The main issue is of *how much* a particular material will
* Damping is provided by providing mechanical resistance to vibrations, and they do so by converting the mechanical energy into heat
* Denser the material, more the energy absorbed per unit surface area. @Navin has used lead sheet in his car (in the past) and in the walls of his speaker cabinets
* Other than vacuum, there is no 'sound barrier'. Anything else will be a damper / 'absorber'. 'Mass damper' is no different from 'sound absorber'. Commercial damping sheets have only 1 layer, not 3 as you assume (ignore the adhesive and the top sheet of polythene or alu foil, which neither form part of the damper, nor are they barriers)

Originally Posted by schakravarthy

... I apologize if you found the statement unwarranted/unjustified. Though I'm not a fan of these products, I too would have gladly embraced the off-the-shelf way, if only it didn't require me to part with so many Gandhijis.

As I had queried you earlier, cost apparently *is* the main driving factor here. Cost, whether low or high, shouldn't be a justification for low effectiveness. Your 'Gandhiji's, your substitute technology! The only thing one can say is use your money sensibly and wisely, sir.

Originally Posted by ::CMS::

I tend to disagree. ...

Err ... what / who with?

[::CMS::]

Originally Posted by DerAlte

Err ... what / who with?

On the problems you had mentioned about using Bitumen sheets for damping based on my experience.

[DerAlte]

Originally Posted by ::CMS::

... based on my experience.

Sure, that's OK. There are more than 20 different varieties, some of which do stink / run, hence tar felt is not generally recommended. Not necessary others will be able to get the same as what you got. The problems I mentioned were cautions against practical possibility, not certainty of occurrence. Indian car manufacturers use tar-felt (mica stabilized) in patches - but apply it before the panels are sent for painting.

[navin]

Originally Posted by schakravarthy

PS- The reason why I dubbed the commercially available products as 'jack of all trades' is that one will, invariably, have to use (and pay!) for all the three layers, viz., mass damper, sound absorber and a sound barrier, irrespective of whether one needs the three layers in his application or not! These products offer a one-fix solution, whatever your need be.

Resonance frequency can be determined by simple mass - spring equations. If you increase mass, the frequency lowers but what also happens given that one has increased mass - one has also increased inertia. Hence more energy is required to excite the object.

Now if we push this further and change the damping coefficient (rubber is high damping and metal is low damping) then the energy required to excite a mass loaded rubber object is much higher than that required to excite an unloaded metal object.

[schakravarthy]

Originally Posted by DerAlte

* Butyl rubber / neoprene is not the 'mass damper'. Rather, it only provides a binding structure for the materials that provide mass
* By itself, the rubber is (mechanically) the equivalent of a spring, so it cannot be a 'damper' by itself.

Quoting from "Design issues in the use of elastomers in automotive tuned mass dampers"-

"Despite the best forethought of designers, unwanted vibration responses can emerge at any stage of a vehicle design. Tuned mass dampers (TMD) and tuned vibration absorbers (TVA) are well known methods to address these issues. Such dampers and absorbers are seldom planned to be included in early design stages. Yet tuned dampers may be the best NVH design alternative and should not be categorized as an undesirable “band-aid” fix. A tuned damper adds an additional degree of freedom. The effect on the response of the original system is to split the original resonance peak into two new resonance peaks, which we call side bands.
The elastomer provides both the spring and damper element"

Mass dampers do indeed exist, they're not a figment of my imagination. Ever wondered why a thin rubber band/ piece is placed at the end of long hollow tubes?

Originally Posted by DerAlte

* *ANY* material, even styrofoam, open/closed-cell foam or paper/cardboard, pasted on to a metal sheet will reduce some vibrations. The main issue is of *how much* a particular material will
* Damping is provided by providing mechanical resistance to vibrations, and they do so by converting the mechanical energy into heat
* Denser the material, more the energy absorbed per unit surface area. @Navin has used lead sheet in his car (in the past) and in the walls of his speaker cabinets

Agree to these 100%.

Originally Posted by DerAlte

* Other than vacuum, there is no 'sound barrier'. Anything else will be a damper / 'absorber'. 'Mass damper' is no different from 'sound absorber'. Commercial damping sheets have only 1 layer, not 3 as you assume (ignore the adhesive and the top sheet of polythene or alu foil, which neither form part of the damper, nor are they barriers)

Quoting from the wiki page,

"There are several basic approaches to reducing sound: increasing the distance between source and receiver, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles, or using active antinoise sound generators."

"The automotive environment limits the thickness of materials that can be used, but combinations of dampers, barriers, and absorbers are common"

Vacuum is an ideal sound barrier. Sound/noise barrier is a generic name.
The commercial products do indeed have three layers. The total material, by itself, acts as a mass damper, the butyl/tar or whatever mixture of absorbing materials is found is the absorbing layer and the aluminum/polythene layer acts as the barrier.

Originally Posted by DerAlte

As I had queried you earlier, cost apparently *is* the main driving factor here. Cost, whether low or high, shouldn't be a justification for low effectiveness. Your 'Gandhiji's, your substitute technology! The only thing one can say is use your money sensibly and wisely, sir.

Yes, cost is a factor, but not THE factor. The main factor is VFM and my attempt is to find a reasonable fix, the DIY way. If I can replicate at least 60-70% of the effectiveness of commercial products at less than quarter of the spend, I would call that value for money. My case is definitely not a 'grapes are sour' one.
The effectiveness of my method might indeed be questionable, but that's no reason for condemning it.

As you very astutely, and rather rudely, pointed it out, it is indeed my money and my idea. So let's leave it at that.

Thank you for your help.

[::CMS::]

Originally Posted by DerAlte

Not necessary others will be able to get the same as what you got.

There is nothing to confuse with the waterproofing tar felts available in the market, if you ask for tar felt for waterproofing you will get the same material everywhere, whatever sample sheets I tried, none were having the issues you had mentioned, tried samples from a lot of hardware/waterproofing shops in Bangalore/Cochin. Some even comes with alum backing.

Originally Posted by schakravarthy

neoprene rubber

As far as I understand, in a car environment the only possible way to damp any metal, esp the doors, is by mass loading. We cannot do any effective absorbing / barrier since there is not enough space to do inside a door. I am doubtful on the sound barrier effectiveness of a thin alum layer than a thick metal sheet and the doorpad after that, yes it helps in reducing the flex caused by the pressure inside the door cavity, but there will not be that much as there are lot of air exits in the door. So ineffect mass loading is the best practical way for damping, either it is a commercial or a cheap DIY effort using Bitumen sheets, the effectiveness will be the same.

But I doubt the effectiveness of the neoprene rubber for mass loading as it is less in density and mass compared to the other solutions.

Apart from that if you want to do any sound absorbing for the outside sound , try it inside the doorpad, not on the outer shell, as you dont need any sound absorption for an IB installation and is not practical to get the desired sound absorption with less depth, it has to be atleast 1/4th the wavelength of the desired freq to absorb.
I am using the Synth wool used for HT room acoustics inside the door pad as it can effectively absorb the mid/high freqs from outside. Moreover it can prevent any kind of rattles due to any loose parts in the door pad, if any. On seeing the usecase, Anwar from TopGear, Bangalore is using it instead of normal foam.

[navin]

Originally Posted by ::CMS::

As far as I understand, in a car environment the only possible way to damp any metal, esp the doors, is by mass loading.

Agreed. In my experience (which has more to do with building home speakers than in car damping) a cabinet (in a car, the door) needs to be stiff and non-resonant. Sadly most materials that are stiff are also very resonant.

Loudspeaker manufactuers and DIYers have experimented with most materials including carbon fiber, corian, stone/granite, fiberglass, and concrete. It is by no accident that wood (MDF or void-free ply) is still preferred by 90% of loudspeaker manufacturers it is reasonably stiff, cheap, damped and reasonably easy to work with. In short it is a reasonable compromise.

Originally Posted by schakravarthy

Tuned mass dampers (TMD) and tuned vibration absorbers (TVA) are well known methods to address these issues.

"The automotive environment limits the thickness of materials that can be used, but combinations of dampers, barriers, and absorbers are common"

The effectiveness of my method might indeed be questionable, but that's no reason for condemning it.

BTW some time back I ran into this company that makes Damping material in India at reasonable cost. It may not be 25% of the cost of Dynamat but I believe it is about 50%. However it also gives at least 90% if not 100% of the damping Dynamat offers. I do not know if you consider that value for money or not but here is the link, feel free to contact them - http://www.dampmat.com/

[schakravarthy]

Originally Posted by ::CMS::

As far as I understand, in a car environment the only possible way to damp any metal, esp the doors, is by mass loading. We cannot do any effective absorbing / barrier since there is not enough space to do inside a door. So ineffect mass loading is the best practical way for damping, either it is a commercial or a cheap DIY effort using Bitumen sheets, the effectiveness will be the same.

Agreed Sir. But don't you feel what I said is similar?
"

• Add a few bits of neoprene rubber (mass damping) to the outermost panel of the door. These when strategically placed, I believe, will reduce the vibration of the door by altering the resonance frequency.
• Next, a layer of neoprene rubber sheet will be used to cover the bare metal parts of the door. This will again act as a mass damper and cut down the vibrations of the door metal."

The pieces I'll be gluing to the outer panel will be quite thick..well, as thick as the limited space can take.

Originally Posted by ::CMS::

But I doubt the effectiveness of the neoprene rubber for mass loading as it is less in density and mass compared to the other solutions.

Neoprene is widely used in industries for sound isolation purposes, therefore, I thought it might be a suitable material. But your bitumen method is interesting. Let me try a mix and match, varying the materials will mean that I can damp more frequencies.
Btw, what's the size and weight of the sheet?

Originally Posted by ::CMS::

Apart from that if you want to do any sound absorbing for the outside sound , try it inside the doorpad, not on the outer shell, as you dont need any sound absorption for an IB installation and is not practical to get the desired sound absorption with less depth, it has to be atleast 1/4th the wavelength of the desired freq to absorb.
I am using the Synth wool used for HT room acoustics inside the door pad as it can effectively absorb the mid/high freqs from outside. Moreover it can prevent any kind of rattles due to any loose parts in the door pad, if any. On seeing the usecase, Anwar from TopGear, Bangalore is using it instead of normal foam.

"Inside the door pad?" I'm confused. All these will be inside, right?
"

• Next will be a layer of the gray closed-cell foam (the kind commonly used in packaging) which I will stick to the rubber layer. This part will act as the sound absorber.
• Another layer of a different foam material will be stuck to the gray closed cell foam layer. This layer too will act as a sound absorbing layer and will further filter the noise.
• Next, I will wrap the inner portion of the plastic panel of the door with neoprene rubber. The rubber will be cut to the contours of the panel and will serve as a mass damper as well as a sound barrier.
• If there's space still left, I will use a thin layer of foam as an additional barrier over the previous layer."

I felt that the rubber will take care of the higher frequencies and the 2 layers of foam will filter the lower frequencies.

Can you please share more details of 'Synth wool'? It sounds interesting.

Originally Posted by navin

BTW some time back I ran into this company that makes Damping material in India at reasonable cost. It may not be 25% of the cost of Dynamat but I believe it is about 50%. However it also gives at least 90% if not 100% of the damping Dynamat offers. I do not know if you consider that value for money or not but here is the link, feel free to contact them - http://www.dampmat.com/

Thanks for the tip.
I'm estimating a spend of Rs.3.5k max for my attempt. Let me try it, if I fail, I can always go the 'usual' way.

[DerAlte]

Originally Posted by schakravarthy

... "Inside the door pad?" I'm confused. ...

I think he means the 'inner surface of the door pad'. Yes, all damping will be inside the door.

Originally Posted by schakravarthy

... Can you please share more details of 'Synth wool'? ...

Glass wool ('fiber glass') was used earlier, but now one uses 'Poly-fill' or synthetic wool - a variety of which is used to fill cushions and pillows. It is wool (as in raw thin fibers, not spun) made from a polymer.

Originally Posted by schakravarthy

... I'm estimating a spend of Rs.3.5k max for my attempt. ...

In that budget, one can use conventional damping material (there is a wide cost range) for the major problem areas, along with - wherever possible - tightly stuffed cotton waste, 'thermocol' and/or closed-cell foam. These are used wherever one has 2 hard surfaces to stuff between, like inside the boot lid / hatch.

There would be some amount of damping already applied by the manufacturer on the floor pan and foot wells - which you should be able to see if you lift all carpets. OTOH, the common places where rattling occurs is behind the FRP claddings on A, B, and C pillars, and a couple of wads of CC foam usually cures them.