Best compound to dampen enclosure?

[3wayaddict]

Hello,

I'll be building a new set of cabinets, the same as my last set but they weren't didn't fit as tightly together as I would've liked. So I'll be building another pair which will then be veneered and finished by Boesch who usually renovate and finish classic Rivas.

When I was putting together my previous pair and I was fitting the Silent Coat butyl damping sheets I noticed that it didn't actually make that much of a difference at all when I gave a knock on the wooden panels. Do you know at wat sort of frequencies butyl damping is most effective? And what are the most effective damping compound to fit in different chambers of the speaker? What would be most effective in a bass cabinet (20 - 300 Hz) and what would be most effective in midrange chamber (300 - 3.000 Hz)?

Would like to hear your suggestions.

[sq225917]

What are cabs made from, whats the internal bracing layout, what size is each box

[Remlab]

A knuckle test is almost totally unaffected by what you apply to the inside of a cabinet unless the wood is extremely thin(think sheet metal). On the other hand, bracing techniques will have a very large effect on wood panels of typical thicknesses. Damping sheets do have an effect though. They help keep acoustic noise vibrations in the volume of the cabinet from transferring into the cabinet walls. Look at it this way, if you apply the sheets on the entire outside of the cabinets and do a knock test, it will have a very clear effect. That's what its doing for the inside of the cabinets.

[chebum]

60 pounds on top of cabinet reduce vibrations a lot. This approach allows to keep the cabinet light and transportable.

[bradleypnw]

Originally Posted by chebum

60 pounds on top of cabinet reduce vibrations a lot. This approach allows to keep the cabinet light and transportable.

Creative solution.

[markbakk]

Constrained layer damping (CLD) is most effective. As is decoupling driver chassis. As is reducing cabinet volume (less area is less radiation). And did I mention bracing?

The simple approach would be to get some Kuiperdecibel. Or use the mass plates from Akoestiekwinkel.nl and glue them between sheets of 8mm ply.

[celef]

Originally Posted by Remlab

A knuckle test is almost totally unaffected by what you apply to the inside of a cabinet unless the wood is extremely thin(think sheet metal).

I think the layer you apply to the inside must be dimensioned to the outer layer, i don not think it will only be effective with thin layers

On the other hand, bracing techniques will have a very large effect on wood panels of typical thicknesses.

i find bracing to work only around the area where it is attached, non braced areas are still hollow sounding

Damping sheets do have an effect though. They help keep acoustic noise vibrations in the volume of the cabinet from transferring into the cabinet walls. Look at it this way, if you apply the sheets on the entire outside of the cabinets and do a knock test, it will have a very clear effect. That's what its doing for the inside of the cabinets.

is this not a bit like cheating, like using a soft foam knuckle compared to a real knuckle, they will of course give different results but the panel has not changed its resonance character

[3wayaddict]

Well let's focus on the midrange chamber. Damping the walls of the bass chamber won't be necessary. The bass chamber is extremely well braced and rigid and it doesn't resonate at all in the first place because of the force canceling arrangement of the woofers.

I'm primarilly looking to dampen all the walls of the midrange chamber. Everything is constructed out of 25 mm HDF. There is a horizontal brace to reinforce the side walls. Of course there will be cutouts, it's just very simplified in the picture. It is shown with the cutouts on another picture. There will also be a vertical brace to reinforce the top and bottom walls, which isn't shown on the picture. So together they will form a cross in the middle of the chamber. The side walls are about 210 mm high, the bottom wall is 250 mm wide and the top wall is 147 mm wide.
So it's really quite well braced and rigid though it still sounds kinda hollow when giving it a knock, which I'd like to dampen.

[markbakk]

Well, that leaves out a few options. I sure would try mounting the midrange 'floating', to reduce vibration transmission from frame to enclosure panels. The panels likely will have quite high resonant frequencies considering the sizes, thickness and material. I guess somewhere around 1kHz. When you are able to create a flexible mounting with fr quite low, say about a few 100Hz and some damping, transmission loss to the panels wil be high.

Of course adding damping sheets will bring reduction of resonances too, but less than the flexible mounting will bring you.

[hifijim]

Here is an interesting thread that dives deep into your question

A Monster Construction Methods Shootout Thread

Bottom line is that Weicon 310M Flex Classic works pretty good, it is not expensive, and it should be widely available in Europe (German company I think).