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There were two construction articles in Radio-Electronics or Popular Electronics, back in the 1980's, featuring a sub-woofer enclosure patented under the name S.A.F.E. or Symmetrical Air Friction Enclosure.

It's author, and patent holder ( I believe it might have been someone by the neme of Papanikolau), was describing in detail how to build this enclosure. Inside there was a system of mazes which alternately squeezed the air through small openings, then let it expand into a wider area, several times, before porting the wave to the outside.

The magazine editors had tested and could confirm that the enclosure produced surprisingly deep bass from a relatively small space. The author was not selling any parts/plans/kits, nor was he advertising anything in the magazine, which lends me to believe their assessment was impartial and not commercially motivated.

I believe I may still have my old collection of mags and could try to locate this info, but it is 1000 miles away from me, in my parents' attic, so I won't get to it for a while.

If anyone has seen these articles (2 of them, a few months apart) or knows where to find them, I think it would be useful information for the group.
If you have a tech library in your area which carried those magazines, and indexes articles by keywords, you might get to this before I do. I think the name of the articles was "SAFE subwoofer". One plan had a side firing driver, the other was firing down from the top.

Good Luck
Thanks for your info., I'm waiting for you to get back to the attic...
Too $$-less to buy the S.Bldr back issues.:ashamed:.
Looks very interesting, I yahooed 'Symmetrical Air Friction Enclosure Loudspeaker' and found this http://americanpowerlight.com/lt-2/lt2-3.html
What a pity that well nigh 20 years passed before interest in this technology was rekindled.

I was beginning to think you had given up on me:).
Here's a beautiful sketch of my prototype.


  • prototype.pdf
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I've found one of the 2 construction articles on SAFE enclosures.
It was in Radio-Electronics of Feb 1982.

I scanned it and I want to post it here, but the attachment limit is 100K.

My scanned pages exceed this, and I cannot reduce the quality or resolution, because there are a lot of diagrams with detailed dimensions which would become unreadable.

Any ideas how we can exchange this kind of information?
Upload the file to an image server.

My interpretation of the Patent:

Make two symmetrical tubes, each tube has a tuned length by the quarter wave equation (same for TLs), Area of tubes must be greater than the volume. Exit port->nothing, Sd->nothing.

Oh, and the tuning of the tube is pretty much up to you, but is preferred to be at least equal to, or, lower than the resonance of the driver being used.

I didn't think that you could get a patent for something like this without at least a loosey goosey mathematical model. It's all words!
Here's my atempt at posting the scanned construction article.

It's easier to visualize the theory of operation here than from the patent documents.
There is a second article, featuring a down-firing woofer, with even better performance, published a few months before or after this one. Still trying to find an old R-E collection...

Len Feldman makes the brutal discovery that you can't reproduce anything at 30Hz, if there is no program content at 30Hz. (OK this was 1982, not everyone had tinkered with subwoofers back then)





This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.