Alternative material for damping

[navin]

Originally Posted by nishantgandhi

Just to bring the discussion to saner and layman's levels - What about those readymade boxes like JBL, Blaupunt and Bassworx?

Most readymade cabinets are made of MDF.

One can make a pretty sane cabinet using a sandwich of 20-30mm MDF and 2-3mm rubber.

[mohang_j]

Originally Posted by navin

Most readymade cabinets are made of MDF.

One can make a pretty sane cabinet using a sandwich of 20-30mm MDF and 2-3mm rubber.

Navinji, /DA/gurus,again Mr.confusion is here.
Which damping material i should use when i am using fiberglass enclosure.

[DerAlte]

Originally Posted by navin

DA you seem to having visions of Bhagwan running around the Mahalaxmi Race Course ...

Yeah, kind of! Jokes apart, I was intrigued - is that for the properties of horse hair (low density, high tensile strength) or that due to the length they would act as supporting scaffolding for the other materials, in effect forming a felt like pad.

Originally Posted by navin

... (1) Stifness and (2) Damping. A box must be stiff so that the walls do not flex and a box must be well damped (wall as well as the volume contained within them) so that the wall do not Resonate. Stiff Walls if not damped will resonate. ...

The wall problem and the damping problem have independent working, though there is an element of interaction at the solution level. I am speaking rather empirically / speculatively, since I don't have the wherewithal to do the equations.

The issue with wall vibrations is most certainly resonances (not the energy), which would have an adverse effect on the music that the box is producing. The 'cosmic' energy in the box has to be reduced to reduce transfer to walls, and the subsequent delayed release.

Wall resonance frequency: Stiffer the wall, higher the f (drum skin logic) so one can really take it out of the sub f range altogether. Also, larger the area, lower the f, so it makes a lot of sense to break large areas into smaller areas using stiffeners or ribs. This is the logic used in body panel damping in cars (folds, corrugations and creases are equivalent stiffeners).

Originally Posted by mohang_j

... Which damping material i should use when i am using fiberglass enclosure.

Conventionally, glass fiber (felt or bagged) or polywool (pillow/cushion filling). Want to try rubberized coir? Try a large enough panel folded in a V behind the sub.

[navin]

Originally Posted by mohang_j

Which damping material i should use when i am using fiberglass enclosure.

glass wool, dacron/polyfil, etc will work best but even these have limited abrobtion below 100Hz. If you want to absorb the energy below 100hz you have to get crazy.

Originally Posted by DerAlte

The wall problem and the damping problem have independent working

Exactly.

The object here is that the walls need to be damped so that they dont resonate, they need to stiff so that they dont flex and the cabinet needs to be damped so that as little energy as possible reaches the walls.

each of these needs a different solution but since they are part of the same system their effects are related.

the trouble as Bhagwan rightly stated is that absorbing energy below 100hz is rather diffcult. One method is to compensate the forces (bracing, push-push, etc) so that they cancel, another is to convert that energy into heat, and lastly what energy cannot be compensated for or cannot be absorbed should be damped by the walls. In the end one needs to implement "a bit of this and a bit of that" to come to a sane solution.

[DerAlte]

And then there are amusing methods (don't try this at home and all that) like one that came to the mind of a classmate 30 years back - "Return to Zero system": DC bias the moving mass so that the 0-cross-over point is moved out XMax / 2; then the cone will be perpetually outside the box, and never transfer any energy to the box (assuming that the DC bias would have reduced the pressure in the box slightly when the cone moved out the first time and the sealing was perfect, the subsequent oscillations are only trying to 'give' energy that was taken away initially - net result: 0 enthalpy or some such crazy idea from a high mind). We tried and tried (mind games, no money) but we couldn't come up with a practical circuit that could do it. It was good as long as the thought lasted.

Theoretically, higher end subs with (linear) servo coil motion control could (must be doing it) compensate for all these myriad issues.

[rider60]

all right i am just having second thoughts on buying the branded regular damping materials now, this thread and shrivz's install are a great inspiration for starters!

now i am going off to look for the dense rubber used to repair the tubes. and i will certainly put up a diy thread on the same!

but i have a few doubts here, should i use the cross link foam layer like shrivz, i am asking again, because navin mentioned that they detoriate and become dust or turn to pieces etc so should i avoid using them?

if so i plan to use only the rubber and a metal layer say aluminium, thats all, would this do just fine? inputs please. gurus?

[kunaldhami]

How effective is the rubber type matirial used under carpet in Home Theater to damp the wheel well and dicky ?

The guy who installed home theater suggested this..Is it a good idea to use it?

[nura]

Originally Posted by rider60

now i am going off to look for the dense rubber used to repair the tubes. and i will certainly put up a diy thread on the same!

Good luck to you. I will be waiting keenly to read your thread.
I tried in vain to locate this kind of rubber sheeting with adhesive in Kolkata. An old gentleman in a tyre repair shop showed me something (he called it kachha rubber) but then demonstrated that it would only stick to rubber & not metal.

[adityamunshi]

Use sheets of rubber and stick them with fevicol synthetic rubber adhesive. Using aluminium will only increase the work without considerable benifits.

I used a 1.5 mm thick sheet of neoprene + natural rubber and its worked perfectly. Plus its incredibly good VFM- 40-50 sq ft for less than 1000. Just make sure the rubber you choose is heavy enough , around 4-5 sq feet per kg is ideal. Check my thread for pics.

Originally Posted by rider60

all right i am just having second thoughts on buying the branded regular damping materials now, this thread and shrivz's install are a great inspiration for starters!

now i am going off to look for the dense rubber used to repair the tubes. and i will certainly put up a diy thread on the same!

but i have a few doubts here, should i use the cross link foam layer like shrivz, i am asking again, because navin mentioned that they detoriate and become dust or turn to pieces etc so should i avoid using them?

if so i plan to use only the rubber and a metal layer say aluminium, thats all, would this do just fine? inputs please. gurus?

Even i had the same experience. Couldnt find sef-adhesive sheets anywhere, bought some kaccha rubber too but it was too smelly to put into the car so didnt use it. But plain rubber sheets with fevicol SR 505 worked well.

Originally Posted by nura

Good luck to you. I will be waiting keenly to read your thread.
I tried in vain to locate this kind of rubber sheeting with adhesive in Kolkata. An old gentleman in a tyre repair shop showed me something (he called it kachha rubber) but then demonstrated that it would only stick to rubber & not metal.

[kURETI]

just do it up with fiber glass mats with resin.

[nura]

Originally Posted by adityamunshi

I used a 1.5 mm thick sheet of neoprene + natural rubber and its worked perfectly. Plus its incredibly good VFM- 40-50 sq ft for less than 1000. Just make sure the rubber you choose is heavy enough , around 4-5 sq feet per kg is ideal. Check my thread for pics.

@adityamunshi - I just went through your excellent thread after reading this post. I will be grateful if you can provide the following additional information.
Do I look for it as rolls (what width?) or as cut-pieces (what length & breadth?)?
What is it "normally" used for?
Thanks in advance,
nura.

[ST7677]

just do it up with fiber glass mats with resin.

I have seen this being done on some foreign forums also. However I would wonder what would happen if the car meets with an accident and the panel needs to be dented and painted. Such treatment may be fine in short run, but in long run will it render the metal panel unsuitable for denting /painting?

[adityamunshi]

Its available per kg, in the form of rolls (4 ft or 2.5 ft wide). But they will give you as little as you want. no need to buy the whole thing.

I dont know what its normally used for but look for rubber shops in the yellow pages.

Originally Posted by nura

@adityamunshi - I just went through your excellent thread after reading this post. I will be grateful if you can provide the following additional information.
Do I look for it as rolls (what width?) or as cut-pieces (what length & breadth?)?
What is it "normally" used for?
Thanks in advance,
nura.

[DerAlte]

Originally Posted by ST7677

I have seen this being done on some foreign forums also. However I would wonder what would happen if the car meets with an accident and the panel needs to be dented and painted. Such treatment may be fine in short run, but in long run will it render the metal panel unsuitable for denting /painting?

Unless the impact is perpendicular to the panel with considerable impact force which can overcome the tensile strength of the glass fibers, it is unlikely to buckle the panel - i.e. panel will bounce back without deforming. Outer metal surface would be 'gouged', but that is repairable. If the impact is severe enough for the fibers to break, it is possible for the denting/painting-wallah to scrape or sand off the resin layer.

And, wouldn't one be better off enjoying months of reduced noise in the cabin than worrying about denting / painting?

[navin]

Originally Posted by kunaldhami

How effective is the rubber type matirial used under carpet in Home Theater to damp the wheel well and dicky ?

It shoud be UV grade sponge rubber

Originally Posted by adityamunshi

I used a 1.5 mm thick sheet of neoprene + natural rubber and its worked perfectly.rubber you choose is heavy enough , around 4-5 sq feet per kg is ideal.

I would suggest something denser than that. 1kg/sq.m is a minumim.

Originally Posted by DerAlte

Unless the impact is perpendicular to the panel with considerable impact force which can overcome the tensile strength of the glass fibers

If the damage is this bad dont they just replace the panel. Opel did that with my wife's Sail.