DIY CLD Plinth Design--A measured Approach

[hjam]

Continuing from #499:

This one shows a 1/2" x 5.7" square piece of Corian on it's own (left side). Note the resonant peaks at 207, 749 and 1698 hz. I'd say the last two will have very low damping.

For the chart on the right, a round piece which I had on hand is compressed via Ductseal to the square one. The added stiffness has raised the resonance (now 2011 and 4019). The more rounded peaks suggest better damping.

Hugh

 

[hjam]

Thanks Hugh, i am not familiar with these plots or their interpretation, does it demonstrate that Corian/Avonite might be a good or poor start point please? - how does it compare? - for a while Corian was thought to be a good start point.
Meanwhile i "dolloped out" some bitumen glue to see what i have, to be honest the smell/volatiles wasn't so bad as the warnings!
It stays liquid a couple of hours and starts to set, question is, is it a V.E. layer at the end, do i aim for a couple of mm? i could fence the edge of the avonite, level it and make a pond before adding the second sheets, i see it as quite practical if its a sound idea!
M

As a starting point, Acrylic seems better than Corian to me.
I do not know if Bitumen acts as a VE layer. The volatiles may also damage the plastics in your Avion. I managed to soften the rubber surround of an expensive speaker years ago using roofing Bitumen inside the cabinet.
I would guess that Ductseal, Greenglue, modelling clay, etc. definitely have that "lossy" action and some may be considered as VE. Not sure.
Whatever you use, I believe you want a THIN layer in between to optimize the CLD effect.
Hope this helps.

Hugh

 

[hjam]

Mike,

Adhering the Ductseal:

Here's a shot of some blobs of Ductseal on a panel. The GB brand stays pliable for a long time, but still gets a bit hard after a few months.

The light green material around the perimeter is Greenglue (which seems to stay pliable much longer). This is my attempt to keep the Ductseal from loosing it's solvents and firming up. I'll probably never know that part really works.

Later, I pressed another panel on to this one and C-Clamped the whole thing for about 10 minutes. The holes you see are to accomodate some 6-32 Nylon bolts to prevent separation later.

Hugh

 

[hjam]

Mike,

You got me wondering why I never tested any Corian. So I did. It'll be quite a while before I calculate any DF numbers, but these charts show part of the story....

This first one is a large 1/2" (12mm) thick piece of Corian. It's resonant frequencies will differ a little from your big pieces of Avion, but you get the idea.

Hugh

Mike,

By the way, I posted that chart to show how a panel of Corian resonates. But, I don't know much about what actually arrives at the stylus. I'm sure there's some some way to measure that before and after you damp your Corian.

Hugh

 

[Mike56]

Mike,

Adhering the Ductseal:

Here's a shot of some blobs of Ductseal on a panel. The GB brand stays pliable for a long time, but still gets a bit hard after a few months.

The light green material around the perimeter is Greenglue (which seems to stay pliable much longer). This is my attempt to keep the Ductseal from loosing it's solvents and firming up. I'll probably never know that part really works.

Later, I pressed another panel on to this one and C-Clamped the whole thing for about 10 minutes. The holes you see are to accomodate some 6-32 Nylon bolts to prevent separation later.

Hugh

Hugh, i tried Blu tack as opposed to the MLV unbonded, it was not as good, i will use a blu tack perimeter to keep it in place and see what happens by tommorrow!!
M

 

[hjam]

If you're going for a two layer CLD, the MLV needs to be removed. The Blue Tack or Ductseal, or whatever needs to be squeezed thin and cover most of the surface.

If it's a 3 layer CLD with MLV in the middle, it still needs to be squeezed down with good surface coverage.

Hope it works!

Hugh

 

[Mike56]

The roofing glue seems to have promise if its visco-elastic, its easy to get a thin coat, more difficult to get it thick, would 0.5mm be suitable?
Which might be best, with the MLV layer or without, i have all the parts, its just decision time!? as you can see it flows out flat fefore it goes off, like self levelling compounds so if i achieve a boundary, then pour it in, leave an hour or so and add the next layer it should do something!
24 hours later we can see whats happened!
M

 

[hjam]

Are those test pieces in the photo? I wonder how well the Roofing glue will cure in the middle. I had that trouble with Green glue and Acrylic. I had to drill some through holes to let it cure. It still took a month!

Some combinations seem to do well as 3 layers, some don't. I suspect Avonite/MLV/Avonite won't be any worse than Avonite/Avonite, so I'd be tempted to go with the 3 layers. Except now I'm thinking the Bitumen may damage the MLV.

What was Clint's line? Are you feelin' lucky?

 

[hjam]

Getting back to Acrylic...

About a month and a half back, I posted some charts indicating that Acrylic/mdf/Acrylic was not damped as well as 3 layers of Acrylic.

Here's an updated comparison. They look similar in the attached. This time, I fussed over which hammer taps I selected. It seems to be harder to get good ones on the Acr/mdf/acr combo.

 

[hjam]

Here's one I like even more than the two above. It's 5 (4"x4") layers of Acrylic, 1/8", 1/4", 1/2", 1/4", 1/8" thick. It's green glue for 3 for the inner elastic layers. It's GB Ductseal for the outer 2 elastic layers.

This combo seems like it extends both the Low frequency and High frequency Damping factor. This may be the combo for the full sized plinth.

 

[hjam]

By the way, the full name of that Ductseal from the package is "Gardner Bender Duct Seal DS-110 - 1Lb Pug". I get it at Home Depot in Canada for $4 - also stocked in the US. Oddly, their web site lists it as DS-130.

I see that an Amazon seller in the UK offers the same thing for 12 pounds. Crazy mark up.

 

[Mike56]

Are those test pieces in the photo? I wonder how well the Roofing glue will cure in the middle. I had that trouble with Green glue and Acrylic. I had to drill some through holes to let it cure. It still took a month!

Some combinations seem to do well as 3 layers, some don't. I suspect Avonite/MLV/Avonite won't be any worse than Avonite/Avonite, so I'd be tempted to go with the 3 layers. Except now I'm thinking the Bitumen may damage the MLV.

What was Clint's line? Are you feelin' lucky?

Yes, pieces to see how it looks and feels.
i agree, logically it seems the volatiles must need to get out, but roofing felt wont let them out either?
Also, whilst roofing felt is not MLV its a similar substance............
I had better try it and see!
M

 

[Mike56]

By the way, the full name of that Ductseal from the package is "Gardner Bender Duct Seal DS-110 - 1Lb Pug". I get it at Home Depot in Canada for $4 - also stocked in the US. Oddly, their web site lists it as DS-130.

I see that an Amazon seller in the UK offers the same thing for 12 pounds. Crazy mark up.

Thinking of Butyl rubber sheets like, visco elastic for sure and used for the purpose on cars?

 

[Mike56]

Thinking of Butyl rubber sheets like, visco elastic for sure and used for the purpose on cars?

The roofing adhesive looks to take ages to go off, even open to the air, so i await delivery of the butyl sheets

 

[hjam]

The roofing adhesive looks to take ages to go off, even open to the air, so i await delivery of the butyl sheets

That should work. Pyramid used something similar when he started this thread. I tried a test piece a while back and it seemed to work.

Home Depot and similar stores sell 6" wide, self sticking (one side) butyl rubber for roof repair, window flashing etc. Is that what you bought? You may need contact cement or similar for the other side.

 

[Mike56]

That should work. Pyramid used something similar when he started this thread. I tried a test piece a while back and it seemed to work.

Home Depot and similar stores sell 6" wide, self sticking (one side) butyl rubber for roof repair, window flashing etc. Is that what you bought? You may need contact cement or similar for the other side.

i ordered a car noise damping kit, we shall see!

 

[Pyramid]

Hey Pyramid, I really enjoyed your research and ultimate building of your plynth - well done and the test jigs are great. During your investigations, did you look at the characteristics of any wood products such as maple, walnut etc. I build many turntables and like the aesthetics of wood. I tend to build them thickly and introduce N0. 11 lead shot into the mix as a dampener. Any thoughts on that approach? Regards John

Sorry of the late reply, I just saw this.

I did not test the property of other woods besides MDF; I believe Bryan (cats squirrel) did a number of tests on his site linked to in the OP.

 

[hjam]

i ordered a car noise damping kit, we shall see!

That sound like a good idea.

 

[hjam]

I spent several hours drilling holes in my sheets of Acrylic. Half of them are for Nylon bolts, the other half are to allow the Green Glue to cure. I'm wishing I'd tested other VE materials (see below), but sticking to what I'm sure of.

Paddy1 suggested a 3M tape in post 434 that sounded good, It also seems to be available in 12"x12" sheets from Digikey.

This Butyl tape combined with some contact cement may have had possibilities too.

https://www.homedepot.ca/product/henry-blueskin-butyl-flashing-4-inch/1001311102

 

[Mike56]

I spent several hours drilling holes in my sheets of Acrylic. Half of them are for Nylon bolts, the other half are to allow the Green Glue to cure. I'm wishing I'd tested other VE materials (see below), but sticking to what I'm sure of.

Paddy1 suggested a 3M tape in post 434 that sounded good, It also seems to be available in 12"x12" sheets from Digikey.

This Butyl tape combined with some contact cement may have had possibilities too.

https://www.homedepot.ca/product/henry-blueskin-butyl-flashing-4-inch/1001311102

Butyl CLD car damping kit has some effect, more experimentation follows