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Rockwool, fiberglass, stuffing the AR-3


VSAT88
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There is still uncertainty as to whether the material was actually rockwool or just an early type of fiberglass. Either way, there is no way to know if the material you have has the same characteristics as the old stuff. The safest way to go would be to use 20 to 24 oz of modern fiberglass in each cabinet. If you are in the US, this amount is approximately 2 1/4 utility bags (per cabinet) of the pink Owens Corning fiberglass sold in stores such as Home Depot and Lowes.

Roy

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1 hour ago, RoyC said:

There is still uncertainty as to whether the material was actually rockwool or just an early type of fiberglass. Either way, there is no way to know if the material you have has the same characteristics as the old stuff. The safest way to go would be to use 20 to 24 oz of modern fiberglass in each cabinet. If you are in the US, this amount is approximately 2 1/4 utility bags (per cabinet) of the pink Owens Corning fiberglass sold in stores such as Home Depot and Lowes.

Roy

Yep, I am in the US, Phenix City Alabama and thanks for the midrange by the way. 

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Hello VSAT88,

Kent and ligs helped me with my first speaker box build and ligs recommended 1Lb per CF of volume ,

so your speaker is 25x14x11.5 = 4025 ci = 2.32 cf  So 2.3 lbs per box APROX.  the product JKent linked to is 2in thick and weighs .4 lbs

I bought this, at 3.5 inches and 7.6 lbs . Had enough to fill  both boxes..

 https://www.homedepot.ca/product/owens-corning-r-12-ecotouch-pink-pak-plus-pink-fiberglas-insulation-15-inch-x-32-feet-x-3-5-inch-40-sq-ft-/1000789365

 

Lonny

 

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Sorry to disagree but 2.3 pounds will be over-damped. Roy is right: 20-24 oz per box. The utility bags he mentioned are not garbage bags but just the small bags of fg sold in Lowes etc. buy or borrow a cheap fish scale to weigh it

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Check that. I figured it out ( I think ) at the second post that he was referring to the actual bag it comes in. Due to the corrosive quality of the original "rock wool" I read about anyway wanted to change it but that is really the only reason. I really thank all of you for your suggestions and support.

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The small Owens fiberglass bags hold about 10oz each. Some Home Depot stores also sell small bags of unfaced yellow fiberglass used for hot water heater insulation. These hold approximately 7 or 8oz, so nearly 3 of these bags per cabinet would be more appropriate. As Kent suggested, a small fishing scale works very well to measure stuffing weight.

When we were putting the AR-3a restoration guide together we conducted many measurements of various types and amounts of cabinet damping material with all iterations of the 12 inch AR woofer. We found that 20 to just over 24 ounces of fiberglass provided adequate fc characteristics in AR-3/3a cabinets, and that variations in this amount did not have much of an effect on the results (less than 1db at 39hz).

It should be noted that earlier cabinets were stuffed with 30+/- oz of material, but later versions were closer to 20oz...and that Tom Tyson mentioned Villchur felt the earlier iterations were over-damped. Subsequent testing by former forum member "Carlspeak" (Carl Richards) confirmed 20 to 24 ounces to be the "sweet spot" with his own testing. Bear in mind, packing the cabinet too tightly with material reduces the internal volume, and has the effect of raising fc and diminishing bass response.

The early material, suggested to be a type of Rockwool by John O'Hanlon during our testing, was found to have higher amounts of sulfur, which he hypothesized was contributing to corrosion of the Aetna-Pollock pots/level controls. Since the posting of our 3a guide, however, I have worked on many more AR models and have found no correlation between the early and later types of AR damping material and pot corrosion. Instead it appears the plating on the pots was simply changed in the mid 70's to be more corrosion resistant. In fact, the earliest level controls (AR-2), which were of different construction, seldom show any signs of corrosion at all.

In my opinion, the worst aspect of the early material is its dust, which becomes airborne at the slightest disturbance. I strongly recommend wearing a mask or working outdoors when handling it.

Roy

 

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