constrained layer damping with MDF and Ply

[Antripodean]

I am looking to bond 8mm HDF (HD3) with 17mm Ply (BB) using green goo. Has anyone else done this? And would this provide me with constrained layer damping for my projects? (OB and sealed bass cabinet)

Once I bond the boards I will be treating it as a 'single' board and use it for cutting, routing & CNCing where necessary.

All thoughts on this are welcome, thanks

[bmwman91]

I think that the biggest challenge will be to get the bonding coverage you want. How viscous/thick is the "green goo" you mention? I think that you will need to be able to apply high pressure evenly across the entire surface of the boards you want to mate.

Also, why not use a single sheet of 25mm MDF? I understand that you are hoping to achieve some elastic damping from the green-goo interface, but I think that the most important thing to go for in bass enclosures is wall rigidity. While it is highly undesirable to have enclosure walls acting as speakers (which the green goo idea might help with), it is also undesirable to have frictional losses in the walls (due to wall resonance/motion) as this decreases the box's efficiency (in this regard, the green goo idea is a real hindrance). In that respect, you would probably want to stick with the "usual" thick walls & bracing type design.

Now of course, if you want to reduce the enclosure's weight, a very thin, very strong adhesive bond between MDF & cabinet-grade plywood might be a good balance between weight & wall stiffness.

[rdf]

Originally Posted by bmwman91

...it is also undesirable to have frictional losses in the walls (due to wall resonance/motion) as this decreases the box's efficiency (in this regard, the green goo idea is a real hindrance).

Say what? How is 'efficiency' being used in this context?

[khush]

Hi there,
Do you mean Greenglue, normally sold for damping plasterboard walls?

If so I have done something very similar. used 12mm birch ply and 2 layers 6mm viroc ( a cement/ wood fibre board). I was very pleased with the result you end up with a material of high stiffness but good damping.

But you will have to rethink ypur method of construction, green glue isn't a glue it remains permanently tacky and will creep. Trying to cut or machine the composite board would be a disaster the greenglue would clog blades or bits.

I found an 18Ga brad nailer to be invaluable for temporarily holding the layers together to rout and in the final asembly. make sure you find something to remove any surplus greenglue, it,s horrible stuff to clean up. I used Goo Gone a citrus based adhesive remover. theres probably something like it in OZ.

Good luk I,m sure you will be pleased with the results.
Khush

[Antripodean]

Originally Posted by khush

Hi there,
Do you mean Greenglue, normally sold for damping plasterboard walls?

But you will have to rethink ypur method of construction, green glue isn't a glue it remains permanently tacky and will creep. Trying to cut or machine the composite board would be a disaster the greenglue would clog blades or bits.

Thanks for all the suggestions. Yes, I do mean Green Glue. I didn't realise it would remain tacky. That would be a real problem in construction.

It seems like my best option is to laminate with liquid nails and use some green glue later for damping where needed.

Good thing I asked

[MJL21193]

Originally Posted by Antripodean

It seems like my best option is to laminate with liquid nails and use some green glue later for damping where needed.

Good thing I asked

I used clear silicone to bond the layers together:

IM001036.JPG

Then light clamp pressure to hold it till it sets:

IM001037.JPG

That was 1/2" particle board core plywood on 5/8" MDF. The silicone is a fantastic adhesive and sets like rubber.

[rcw]

By far the best scheme is as bmwman91 suggests, just make the panel thicker.
The so called constrained layer damping used by speaker builders is in fact mass damping.
If you look at the hysterisis curves, the materials used in for instance plasterboard constrained layer damping, are not deflected into the hysterisis region by the small displacements found in speaker cabinets.
rcw.

[bmwman91]

Originally Posted by rdf

Say what? How is 'efficiency' being used in this context?

My comment was with respect to the "sealed bass box" portion of the OP.

[Ed LaFontaine]

MJL211093 posted:

The silicone is a fantastic adhesive and sets like rubber

Finally, something I can agree with you on. I used it between 3/4" mdf & 1/4" durock (ceramic tile underlayment).

[MJL21193]

Originally Posted by rcw

By far the best scheme is as bmwman91 suggests, just make the panel thicker.
The so called constrained layer damping used by speaker builders is in fact mass damping.
If you look at the hysterisis curves, the materials used in for instance plasterboard constrained layer damping, are not deflected into the hysterisis region by the small displacements found in speaker cabinets.
rcw.

I don't agree, not at all and the reasons are fairly obvious.

Originally Posted by Ed LaFontaine

Finally, something I can agree with you on.

I'm sure we would agree on a few things Ed. I like the Durock idea.