AR4x rock wool replacment

[Guest tonyd]

Found another set of AR4X's today.Going to pull out the tweeter controls to clean up.I don't want to reuse that nasty rock wool,is their another choice for the stuffing or how much to put in.

[johnieo]

Found another set of AR4X's today.Going to pull out the tweeter controls to clean up.I don't want to reuse that nasty rock wool,is their another choice for the stuffing or how much to put in.

Hello Tony:

Villchur designed all the early speakers to operate with fiberglass stuffing. At some point after he left the company--for a period of about two years--rock wool was substituted. The reason I am told was that fiberglass was in short supply. Villchur indicated that rock wool never gave the kind of effective box size increase needed for its characteristic low bass as did fiberglass and for that reason he would not use it. My micrographs of the two fibers show clearly that fiberglass was a consistently sized fiber of order 2-to-5 micrometers diameter, wherease rock wool had large "blobs" in it of order several hundred microns diameter, because it is made from rock and refinery slag and not a simple glass. This translates to less fine fiber diameter per ounce of rock wool than for fiberglass. It is the fibers, not the "lumps" that are interact with sound waves in a desirable way. So yes, trash the rock wool and use fiberglass.

Early AR-4x speakers used 18 ounces of fiberglass; later after serial numbers of order 235,000-250,000, AR reduced the quantity to 11-12 ounces in order to increase, slightly, the overall Q of the speaker. Home Depot sells fiberglass in small packages called "Handy Packs" or some such name that weigh 11 or 11.5 ounces. This is a perfect way to purchase fiberglass if you have no other need for it, as the material in those packs has no backing paper to peel away. A few more dollars, but nice as there is no waste for such a small project. Two packs will do the job, one in each cabinet. As we have noted elsewhere, work outside or in the garage, wear a dust mask and a pair of plastic disposable gloves. When done wash hands in cold water as it closes pores of skin and prevents future itching. Very nice speaker; it will deliver great sound.

Some have suggested replacing the fiberglass with polyester; this is not a good choice as polyfill will not deliver the original bass.

Cheers,

[genek]

Some have suggested replacing the fiberglass with polyester; this is not a good choice as polyfill will not deliver the original bass.

I wonder what the availabiity of the poly that Ken Kantor was referring to here is these days.

http://www.kenkantor.com/press_clippings/s...er_stuffing.pdf

[Carlspeak]

Almost everything you ever wanted to know about box stuffing can be found here

http://auralization.blogspot.com/

Much of the work posted there was done by Johnieo.

[johnieo]

I wonder what the availabiity of the poly that Ken Kantor was referring to here is these days.

http://www.kenkantor.com/press_clippings/s...er_stuffing.pdf

I believe Ken was referring to duPont "Hollowfill" I cannot find information about it or where it is to be found. My contacts at duPont are either retired or dead, so I guess that tells you something about me! My gut feeling is that the hollow fibers act as small reservoirs that allow air to flow in and out with some phase shift compared to that of the main cabinet's pressure changes, thus giving some effective energy storage and release; would be wonderful if we could find it, but perhaps they no longer make it???

Cheers,

[Guest tonyd]

Thanks for the response guys.John I'll try home depot or lowes tomorrow for some fiberglass packs,with some luck I'll find some close by.These ar4x are the second set I found this week.

[oldguide]

Hollofill was a fiber Dupont invented to replace down in sleeping bags and jackets. It has since been replaced by better and more high tech stuff. Different manufacturers have different versions, but the principles are much like hollofill. I don't know if you can buy the stuff raw, but I would assume so.

[Mazeppa]

I was thinking of doing the polyfill thing to a pair of AR2a until I found this thread. The attached link was very informative as well. Fiberglass it is for my AR speaks. Thanks again to the AR gurus.