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The Blue Jeans Placebo Effect--AR3 Stuffing


oldguide

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I finally had to bite the bullet and replace my AR3 pots which were too far gone. Thanks again to all who put the guide together. It was much help.

In the process of doing this, I again faced the task of stuffing the speakers with insulation. Instead of the standard fiberglass, I used some newer insulation made of recycled blue jeans which I had left over from a home remodeling project. It is non-scratchy, non toxic. However, it is also slightly heavier than fiberglass per square foot. This left a choice of replacing the old stuffing by volume or by weight.

The solution ended up being splitting the difference, i.e. slightly less volume, slightly more weight. I will leave it to the experts to weight in on whether that was the right solution. My tired old ears do not notice the difference. Perhaps there is a placebo effect operating?

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I believe Carl said stuffing is not an exact science ... so as long as you are happy...

I replaced the rock wool in a 4x recently with polyester pillow stuffing without bothering to measure it other than not packing it tightly. Sounds great to me ... could it be improved ... maybe ... in the meantime though I will be enjoying its sound.

Roger

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I just recently stuffed another pair of AR3a's withe 14 oz. of Acousta-Stuf which replaced 33 & 34 oz. of wool respectively.

This is the 3rd pair of Ar3a's that I have opened up.

Each time I carefully weighed the stuffing, and each time it has been different.

Within each pair, it was never exactly the same amount.

I think Carl got it right.

You could probably measure a difference in box resonant freq, but in the real world of dynamic music, coupled with the subtleties of the bass frequencies, the difference is most likely undetectable.

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Perhaps Advent did the right thing by switching from FG to foam blocks. Two problems were solved. Potential OSHA issues with workers handling the FG plus plant environment and, consistency of the stuffing amount.

Any particular foam? I may try that one ...

Roger

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It must be open cell foam. Don't know the exact specs (density, etc.). If you have FG now, keep it. It's better than foam.

Agree. When I restored/modded my OLAs, in addition to all new LCR components I stuffed them with fiberglass, which I believe Carl, PeteB and others had recommended. The foam looked like old-style mattress foam. If you happen to have an Advent 400 radio speaker it has the same foam.

-Kent

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  • 1 month later...

I happen to like that recycled cotton denim insulation, but I have never used it in speaker cabinets.

About the Advent stuffing, I have two pairs of Smaller Advents, with the following differences:

Pair 1 - 1972 models, green tweeters, 8uF and 16uF cap, fiberglass stuffing (one pink, one yellow).

Pair 2 - 1975 models, red/orange tweeters, 4uF and 8uF cap, foam block stuffing.

post-112624-0-11805200-1444833885_thumb. post-112624-0-88394500-1444833939_thumb.

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Most do-it-yourselfers will have a natural tendency to believe that anything they change will be an "improvement," even if objective evaluation shows it is not. This is not just an audio phenomenon. Look at really, really old copies of magazines like Popular Science and see how long advertisers have managed to convince people that installing things like magnets into their cars' fuel lines will improve horsepower or fuel economy.

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