Foam prototype

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Hi everyone. Decided I needed to get more familiar with the BIB principle and started building prototype speakers in foam. I had a brief career as a prototype builder and foam is an awesome material to work with. Quick and easy, cheap, u can repair any effups with expanding foam.

Found a pair of $2 three inch units at a salvation army store, some foam sheets at the lumber yard and fired up the hot wire. Turned out that was a two man job so I had to make do with a jig saw + exacto knife

I have absolutely no info on the speakers other than whats printed non them but I checked some other three inchers and winged the specs. Heres some pix

Car battery charger plus hot wires
First batch
This was after I vacuumed the saw. Cutting in foam gets really messy


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Gonna mount a hard wood supraish baffle so they´ll get very front heavy so Im gonna need some sort of bottom plate. SPeaker will be way to low for proper listening but nothings really proper with this prototype anyway.

The speakers
Rough fitting. That skewded right side of the baffle was cut with the hot wire. Next to impossible to get straight with just two hands
Glueing sides + back
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Didn't GM's Saturn division build motors out of styrofoam? I think i remember someone telling me they poured a chemical onto the foam to harden it.

No idea. But its used the other way around in Lost Foam Casting. That and wax. U make a mock up of what u wanna cast, build up material around it, plus a tube and pour metal in the tube. The foam disolves and ur left with a finished product. An engine block for example.

This the the first speaker Ive built in foam. The styrofoam resonates in the upper bass + lower mids and its way, way to light. Needs to be glued to a heavy base plus I didnt have any driver specs to go by. But it was a really quick and easy to build, I got a dry run on building a BIB and Im watching Avatar listening to them now. Theyre truly musical and amazing in so many ways.

Now a BIB is an easy build. But anyone into more complicated cabinets should definitely try using foam for dry run builds and tests. Maybe use a denser foam that´ll resonate less, I got a rather soft one cuz of price and availability, $1.50 for a 600x1200x30mm sheet. Its silly easy to work with, mistakes are easily rectified. I cut a hole for the speaker in the back instead of the front baffle, glued it back in seconds with expanding foam. Just be careful what glues, paints, solvents etc ur using since foam disolves into nothing in no time at all.

Next up. Even bigger BIBs in proper wood :)

Regards /Bo
GREAT OLD weems link there! fascinating

Indeed, there were others too, but my early magazine collection went up in smoke back in '72, so unfortunately only have this one thanks to Freddy Ireson (FreddyI) for sharing it some years ago.

WRT to 'glassing it over, probably not worth the extra effort/cost since it was designed for the ~2-3.0 Qts console drivers of the day. Norman C. Fulmer's K-slot corner loaded TQWT would be a much better choice, though sims best using a relatively high Vas (HE) woofer such as the old Altec 421 series MI driver (scroll down): Karlson speaker project

Could be cool to fiberglass over that and see how it stiffens up.

Not sure wether ur refering to my flimsy styrofoam thingies or GMs link to the corner speakers. However. What little structural guessing I ran in my head during this project, fibre glass wouldnt be so beneficial. Most probably just raise the resonance frequency and tightening its Q value

Regards /Bo
Minor mods

Cut out the dustcap and tried some different pieces I had lying around. Settled on metric sockets. Cleared up the upper mids and treble more than I imagined. Also swappped the JRC4558 op amp for an OPA2134. Again much improvement

Close up of socket
Speakers in room corner. The tape isnt holding the baffle in place, its glued on. Havent bothered removing it :p
The fix I mentioned earlier where I glued back a piece


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