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Kempac Replacement


oldguide

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Has anyone ever though about using Tyvek as a replacement for Kempac? Tyvek was first used in house building as a breathable moisture barrier, but now they use it for everything from boat covers to envelopes to the protective moon suits worn by people working with asbestos. It lets air through but nothing else and lasts forever. The problem is that it usually comes in huge rolls for home siding, but I happen to have part of a roll left over from a building project and have thought about using it instead of the Kempac I managed to recover. The Kempac has deteriorated a bit and I noticed some of it had stuck to the woofer and even pieces underneath the protective screen. Tyvek would essentially shield the woofer from everything but air.

Chemically it is spun Olefin. The question would be does it allow enough breathability? The info I could find says what is known as the perm factor ranges from 0-1 with zero allowing anything through and 1 allowing nothing through. Tyvek rates in the middle at .58, allowing air and moisture to pass through, but remaining impervious to rain, dust, etc. I've heard it described as Gore-tex for houses.

So you old hands at AR, would Tyvek work?

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So you old hands at AR, would Tyvek work?

I'm skeptical about the suitability of Tyvek. It is rather stiff and crinkly, and not very porous. John O'Hanlon and/or Roy Champagne (2 authors of the wonderful AR 3a restoration manual) have recommended crinoline available from fabric stores:

http://www.joannfabricsandcrafts.com/joann...PRODID=prd23658

Alternatively, I have recommended fiberglass window screening. That is what was used in the Allison: Four, and I would respect Roy Allison's choice of materials. The screening is cheap and durable.

Hope this is helpful

Kent

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I'm skeptical about the suitability of Tyvek. It is rather stiff and crinkly, and not very porous. John O'Hanlon and/or Roy Champagne (2 authors of the wonderful AR 3a restoration manual) have recommended crinoline available from fabric stores:

http://www.joannfabricsandcrafts.com/joann...PRODID=prd23658

Alternatively, I have recommended fiberglass window screening. That is what was used in the Allison: Four, and I would respect Roy Allison's choice of materials. The screening is cheap and durable.

Hope this is helpful

Kent

Hi Kent;

I will agree that Tyvek may not have the silent quality needed, in case it should touch the woofers frame.

The fiberglas screening material is, what I believe, was also used for the AR woofer's frame opening shielding for fiberglas and wires protection.

I will add to this list, slightly.

Old burlap sacking, as used in old potato sacking and no-seeum netting, as used in camping, for insect protection, are suitable as well.

A slightly thinner version of Kempac is still available at most all larger lumber yards.

This is still used as handtowels and is about 12 - 16" square.

I believe that, Tom Tyson, wrote last year, about Kempac still being manufacturered in larger pieces and larger quantities.

With other more readily available sustitutes being available, we now have many suitable options.

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I worked in the nonwovens (Tyvek is technically a nonwoven) industry for many years and am certain it would probably do more harm than good. Compared to window screening and that creped, brown paper used originally and is still available, it is essentially not porous. Yes, it does allow air thru, but at a very low rate suitable for house wrapping and protective clothing.

However, for the fast paced cycling of a woofer back wave - no way. It simply couldn't handle it. The back wave would be deflected to the sides rather than directly into the stuffing as it should be.

As Tony Soprano would say: Faaagettaboutit

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Guest Terry Again

Please forgive me for asking a question about this,as I have only owned 1 pair of AR's and the ones I have had No "sock" over the woofer and there was just the fiberglass inside so I have little idea of what this topic is about though I feel I should have some And wonder how and where it should go?

Thanks,

Terry

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Please forgive me for asking a question about this,as I have only owned 1 pair of AR's and the ones I have had No "sock" over the woofer and there was just the fiberglass inside so I have little idea of what this topic is about though I feel I should have some And wonder how and where it should go?

Thanks,

Terry

It's just a simple, albeit highly porous, barrier to help keep the fiberglass out of the woofer's rear side. A piece of kempac is cut a couple of inches larger than the woofer hole cut in the cabinet and placed on top of the fiberglass just before installation of the woofer.

Now, exactly why AR used kempac IN ADDITION to the screening they glued to the backside of early woofer frames is a mystery to me.

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Thanks again for all the help. As I have said before this place is unbelieveable.

Carl, you sort of confirmed my intuition on this, plus the data that show only 50% air permeability. Obviously from what you say, you need more than that. In fact it sounds like the more air transfer the better.

The noseeum netting is an interesting idea, as I have some of that around ( hence the handle).

But my inclination all along has been to go with the "book" as I call it, so I will probably seek out some fabric at the fabric store (need some for the grills anyway).

Actually my Kempac isn't in that bad a shape and I have seen it also at auto repair places where it is used to absorb grease and oil.

I think this subject is closed.

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Thanks again for all the help. As I have said before this place is unbelieveable.

Carl, you sort of confirmed my intuition on this, plus the data that show only 50% air permeability. Obviously from what you say, you need more than that. In fact it sounds like the more air transfer the better.

The noseeum netting is an interesting idea, as I have some of that around ( hence the handle).

But my inclination all along has been to go with the "book" as I call it, so I will probably seek out some fabric at the fabric store (need some for the grills anyway).

Actually my Kempac isn't in that bad a shape and I have seen it also at auto repair places where it is used to absorb grease and oil.

I think this subject is closed.

Hi there;

I'm certain the auto shop towels you found are the same one's I found at our local Rona big box store.

Too bad the box full is so large, there's enough to do one heck of a lot of speaker systems.

When I mentioned that Tyvek may not be suitable for a back sheet, I was not even considering air permeability.

We are talking about a loosely layed in sheet, behind the woofer, not duct taped or glued to the woofers frame where air infiltration would then be needed.

The only concern I have is, if the Tyvek should loosley touch the woofers frame, it would be the cause of a resonance buzz, it would be a noisy material rather than all other softer materials mentioned.

I feel that the, glued onto the frame holes, plastic/fibreglas fly screen netting, is the best, it prevents anything from entering the holes, both wires and insulation.

At the AR factory it was obviously labour intensive to cut the 4 pieces and apply with glue.

The glue would need to dry somewhat so that the pieces did not fall off after woofer installation.

If we were talking about Dynaco A-25 cabinet vent opening covers, Tyvek would not be suitable as well.

Just a thought.

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I don't think all AR woofers had the screening glued to the backs. My set of 3A's have the Alnico woofers - they did not have the screens or any sign of them when I pulled them - just the kempac paper (didn't know that's what it was called) between the woofer and fiberglass.

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I don't think all AR woofers had the screening glued to the backs. My set of 3A's have the Alnico woofers - they did not have the screens or any sign of them when I pulled them - just the kempac paper (didn't know that's what it was called) between the woofer and fiberglass.

I replaced the woofers from my mid-70's AR-2ax's back in the 90's. Neither the originals nor the replacements had any screening or paper; they were just open in the back. And the stuffing in my boxes wasn't fiberglas; whatever it was, it was soft and didn't shed those nasty little fibers that get into the skin and make it itch after you touch it. It was also denser than the fiberglas that comes in rolls for insulation.

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Hey! Oldguide said this thread was closed! :)

Some early AR woofers did have plastic screening glued to the backs--Here is a woofer from an early 2ax.

That itchy stuff may have been rock wool. Do a search and you'll find that it should be replaced with fiberglass because the chemical properties of rock wool caused corrosion. Or, it may just be very crumbly fibreglass.

Vern mentioned some more good alternatives to Kempac. I think anything that is acoustically tranparent should work--even an old scrap of grill cloth--some some sort of fine netting such as the mosquito/noseeum net or crinoline should be good. A trip to a fabric store should allow you to buy just the small amount needed, very cheaply.

Kent

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That itchy stuff may have been rock wool. Do a search and you'll find that it should be replaced with fiberglass because the chemical properties of rock wool caused corrosion. Or, it may just be very crumbly fibreglass.

The stuffing in my 1975 2ax was soft and non-itchy, and appeared to be 2-3" thick sheets that had been folded over multiple times to make a loose bundle that had been pushed through the woofer opening and then fluffed up again inside the box. I was working part-time in a Radio Shack store during my college years, and they sold bags of speaker stuffing that looked just like the stuff that was marked as "100% polyester."

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I don't think all AR woofers had the screening glued to the backs. My set of 3A's have the Alnico woofers - they did not have the screens or any sign of them when I pulled them - just the kempac paper (didn't know that's what it was called) between the woofer and fiberglass.

Hi there;

If we put our heads together we can look at what may have happend at AR regarding the glueing of screening to the frame openings and the sheets of Kempac.

The gray screening pieces were either stamped out of sheet's or handcut, and then glued to the frames.

Labour intensive to be sure, the material cost was negligible.

I may be wrong but I prefer this method.

The Kempac was pressed into the woofer opening and laid out with the wires through an opening in it's center, probably done with a finger.

Cost maybe very slightly more than the screening material but much faster to install, less labour cost's.

Kempac was also used in the Heathkit/AR speaker kits.

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The stuffing in my 1975 2ax was soft and non-itchy, and appeared to be 2-3" thick sheets that had been folded over multiple times to make a loose bundle that had been pushed through the woofer opening and then fluffed up again inside the box. I was working part-time in a Radio Shack store during my college years, and they sold bags of speaker stuffing that looked just like the stuff that was marked as "100% polyester."

oops--I misread your post, gene. Clearly you wrote "stuffing in my boxes wasn't fiberglas; whatever it was, it was soft and didn't shed those nasty little fibers ". My mistake. OTOH, I don't think polyester was used in AR 2ax speakers and John has done an analysis that found polyester and fiberglass don't have the same sonic qualities. This is a mystery. Were you the original owner of those speakers? I wonder if the stuffing was replaced. hmmmm.....

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oops--I misread your post, gene. Clearly you wrote "stuffing in my boxes wasn't fiberglas; whatever it was, it was soft and didn't shed those nasty little fibers ". My mistake. OTOH, I don't think polyester was used in AR 2ax speakers and John has done an analysis that found polyester and fiberglass don't have the same sonic qualities. This is a mystery. Were you the original owner of those speakers? I wonder if the stuffing was replaced. hmmmm.....

Yes, bought them brand spanking new in '75, and they were never opened until I changed the woofers in the early 90's. I'm not saying that the stuffing was polyester, just that it looked like the poly that the shack was selling and was definitely not rock wool or fiberglas or anything else that shedded crumbly bits into the box or itchy bits into the skin.

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Hi there;

If we put our heads together we can look at what may have happend at AR regarding the glueing of screening to the frame openings and the sheets of Kempac.

The gray screening pieces were either stamped out of sheet's or handcut, and then glued to the frames.

Labour intensive to be sure, the material cost was negligible.

I may be wrong but I prefer this method.

The Kempac was pressed into the woofer opening and laid out with the wires through an opening in it's center, probably done with a finger.

Cost maybe very slightly more than the screening material but much faster to install, less labour cost's.

Kempac was also used in the Heathkit/AR speaker kits.

Hi again;

We may as well use the original material that Edgar Vilchur used in his prototype speaker system.

Cheese cloth, it is available in every paint store and probably general and big box stores everywhere.

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