Sound proofing / deadening

[Thor]

It would be typical for these tanks to be made from tin or lead coated steel.

In the UK, a range of sound proofing materials is available from 'Noise-Killer Acoustics', but it is not cheap.

A relatively cheap way to achieve quite a lot (but not necessarily eleiminating sloshing noises) is to use the foil and bituminous product which builders use for 'flashing' (that is sealing) around things like a vent pipe passing through a roof. This used to be called Flash-Banding, but I am not sure what the current brand name is now. It is available in rolls of various widths. Unfortunately you will get the best effect by using a rather wide piece, carefuly stuck on, eliminating air bubbles, etc. accros the middle of a panel. There is no need to accurately cover the panel right to its edges, but it is worth having a large area covered in one continuous piece.

The mechanical theory is that if the panel is driven to vibrate the small bending of the panel which this entails causes the apparent relative lengths of the panel and the foil to change. Since the foil is relatively stiff in tension, the vibrations cause the panel and foil together to try to squash the soft bituminous material in between. This requires a huge amount of energy, so the panel vibration is very effectivly damped.

I hope that helps.

Thor.

[Kevin H]

Originally Posted by Thor

A relatively cheap way to achieve quite a lot (but not necessarily eleiminating sloshing noises) is to use the foil and bituminous product which builders use for 'flashing' (that is sealing) ...

There's a brand here called Flash-Tac, I have some on my garage roof.

However, I thought mass was an important factor. Being that the heavier the panel the greater amount of energy is required to cause it to vibrate, and that flash tac stuff isn't very heavy.

That's why I came up with the idea of sticking lead flashing to the tank. Maybe I should bite the bullet and give it a go.

Incidentally, a word of warning to anyone who decides to remove the original horse hair. The bulk of it is easy to remove but I tried removing the remnants of it stuck to the rear bulkhead on my car. I used a Xylene based product, which is brilliant for removing the old brown rubbery glue which was widely used on British cars of that era, but there was also some black stuff on my bulkhead, possibly some sort of underseal, and mixed with Xylene and horse hair makes a horrible black sticky mess!

[412usa]

While I think that the ideas for soundproofing are ...sound, I know that the
tank on the 412USA is aluminium and have just checked a spare tank I have
for the 405's and there is no magnetic attraction. It seems to Aluminium. I
don't see why they aren't all the same. Not that that solves the sloshing
problem.

Peter

[Kevin H]

Just did the magnet test on mine and it is most definitely iron/steel.

If they made them out of different material it begs the question - did they make them with differing internal baffle design?

[Thor]

Yes, mass also helps, but the concept of two relatively stiff sheets sandwiching a softer layer does create good damping, so do try it because it is a really easy thing to do. You have to use a product with a good tough outer foil layer, not some cheapo stuff. The materials used by builders should be tough, being left outside for years in use, but the stiffness of that layer is what makes the product work in sound deadening situations.

I know the tank of my 409 is steel.

Thor.

[Kevin H]

Originally Posted by Thor

Yes, mass also helps, but the concept of two relatively stiff sheets sandwiching a softer layer does create good damping, so do try it because it is a really easy thing to do. You have to use a product with a good tough outer foil layer, not some cheapo stuff.

But isn't adding mass directly to the panel that is vibrating a different approach to suspending a mass parallel to that panel ?

In the first instance you are reducing the noise at the source, because it takes more energy to vibrate a heavier mass (I believe that's why they mount building air conditioning compressors on concrete slabs).

Whereas the second instance - a suspended mass (with a decoupling layer as Philip said) - is good for stopping sound waves travelling further once they left the first panel.

I would have thought the best solution would be both.

As for the Flash-Tac product, it doesn't really meet the criteria to my mind. Firstly the bitumen isn't very thick and isn't very soft as the decoupling layer, not like some sort of foam rubber for example. Also the metal foil layer doesn't seem very substantial, at least not on the product I am thinking of.

Anyway, I've decided to go down the lead route. I already went out and bought some lead sheet last night (15kg/sq m) plus some high strength building adhesive.

I shall report back!