Best CLD = “30# roofing felt”? “30lb. tar paper”? - diyAudio
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Old 13th December 2004, 01:35 AM   #1
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Location: dry ol Melbourne Australia
Default Best CLD = “30# roofing felt”? “30lb. tar paper”?


Some of you will have read Art Ludwig's very informative article “Construction of the Loudspeakers”, where amongst other things, he gives the results of testing different approaches to constrained layer damping:

The best results were with the inside lined with “30# roofing felt”. I’m told this is “30lb. tar paper”, but what is tar paper? I’ve searched this forum, and got just partway to an answer.

What is asphalt roofing (apparently used instead of small shingles)?

I live in Australia, and have heard of neither product, though I’ve never been in those parts of the hardware store. I’ve heard of :
- sarking (insulating felt and weatherproofing, prior to tiling a roof) but that doesn’t sound right.
- flashing (some sort of sheet metal used to reinforce and weatherproof the joints and angles of a roof)

I have heard the best not expensive, non-hardening ‘glue’ used to between the layers is 'Liquid Nails’.

I also see reference to 50lb “roll roofing” and “rubber roll roofing”. Apparently roll roofing is compressed felt saturated with blown asphalt, though it’s debated whether it is suited for damping, more as a filler in a plywood 'sandwich'.

** Can someone describe of the best everyday lining materials, and what these products are made of?

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Old 13th December 2004, 04:27 AM   #2
azira is offline azira  United States
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What are your roofs made of in Australia? We have something called composite roof shingles. They are made of sort of a thin layer or tar covered with something similar to sand. They are pretty thin, about 1/4". Other common types of roofing would be cedar shakes or sheet metal. Also thick tiles.

Anyway, when we put down composite roof shingles, we have to put down some felt paper beneath it. It comes in different weights and thicknesses. At your local hardware store, go to the roofing section and look for some rolls of black sticky felt paper. It comes in roles of about 3-ft tall and 8" across.
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Old 13th December 2004, 04:40 AM   #3
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Hi Danny

> What are your roofs made of in Australia?
Most modern houses are cement or concrete tiled, though some in a nostalgic style use sheets of corrugated iron (which has usually been plated in a coloured ‘heritage’ style).

Very few are shingles, though sometimes sold slate roof buildings need re-roofing. This material may be needed under slate roofs. If a normal hardware store doesn’t have it, I’ll try a slate roof specialist.

So it’s tar that’s added to the felt paper that makes it black & sticky?
What determines it’s weight – the thickness of the felt I assume.
And a recommended weighting - 30 pound, is that 30 pound per . .?

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Old 13th December 2004, 06:02 AM   #4
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Default Aussie speaker builders:

Bunnings (over the phone) is suggesting Malthoid as a bitumen impregnated fabric that has properties like “roofing felt”
It’s 1-2 mm thick, and comes in 20 m * 220 mm rolls for $11.
It’s used amongst other things between concrete and timber, and restoring roofs.

Anyone use this? I imagine you’d need 2-3 thicknesses.
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Old 13th December 2004, 10:13 AM   #5
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Other question: “30lb. xx paper” – is that 30lb per square or lineal foot?

Apparently in a sealed cabinet the petroleum like gasses from the bitumen can damage drivers.

But supposedly linoleum has a similar density to bitumen impregnated fabrics.
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Old 13th December 2004, 11:24 AM   #6
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Here in the UK, 'Roofing Felt' comes in big rolls, and is the stuff that is put on the roof before the tiles are put on. It forms a water resistant barrier. It seems to be a thin synthetic fabric, impregnated with asphalt, and dusted with a powder to stop it being sticky. It's only thin, about 3mm.

I would have though most countries would have something similar.
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Old 13th December 2004, 03:37 PM   #7
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Although I can't suggest what is best for speakers, I can fill in some of the blanks about roofing materials. This is a very brief explanation.


Tar is no longer used much. It has been mostly replaced by asphalt. Often you still hear the term tar being used. As in tar and gravel roof.

#30 roofing felt is an asphalt saturated cellulose felt. It is not paper. Paper and felt are different Paper fibers and tighter and have greater structural value and are 'stiffer' than felts.. Asphalt paper goes on the walls behind your siding, felt goes on the flat or low slope under your roofing material.

There are also a fiberglass and polyester scrims coated with asphalt and still called felts.

Flashing basically means "goes up" It can be membrane flashing or sheet metal flashing. Flashing that covers over and goes down (like a cap over a railing) is called counterflashing.

#50 Roll roofing is the same as #30 just thicker. It sometimes has a granular surface to protect it from the UV rays. #90 is a more common type of roll roofing. It has a granular surface.

Rubber roll roofing is a synthetic product made of EPDM. It looks and feels like sheet rubber.


The composite shingles of which you speak sound like ordiinary asphalt shingles which start with a saturated felt or fiberglass scrim, add a layer of stiffened asphalt on either side and put granules on the top side for colour and UV protection.


The 30 lb refers to the old days when 100 square feet of it weighed 30 lbs. This is an old term. It no longer weighs that much. It is now refered to as #30 or #50.

Malthoid is not a product I am familiar with. Perhaps it has a different name in Canada.

I wouldn't be worried about a gas off with just felt in the cabinet. That would apply more to the self adhesive bitumen membranes that utilize a cut back asphalt as the waterproofer and adhesive. It is full of solvents that might have adverse effects.


If the supporting structure is synthetic, the felt is said to be coated. If it is organic, it is saturated. The material used to prevent it from sticking to itself when freshly rolled up is called 'sand'.

Unfortunately, after all that, I still can't help you decide what is the best product for inside a box. It's funny, the thought of using roofing materials inside a box never occured to me, although it does get mentioned here from time to time.

Good luck with the projects.

planet10 needs your help:
Let's help Ruth and Dave
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