These are the prototypes for hls. Pictured here is the unfinished (no vent) for the a's.

In the pic link the small round one was made 1st for the c's. As you can see, my moto tool skills in the slots leave something to be desired. It's not clear in the pic, but the venturi mouth is sweet.
I ordered the exchangers for the a's after I'd already picked up the c's. He said he had some 1-1/2 hex stock and would that work. I said sure. They kick ass. Big enough I can machine the slots with a router. I'm going to have the c's remade with it. If I had the bucks I'd just have him machine the flats in a v leaving a 6 pointed star, and then I wouldn't need the old heatsinks I robbed from a bunch of old stereos and tvs I'm going to mount on them. He's pretty excited about it too, and may just do that anyway on the new ones for the c's.

Testing starts this weekend. Probably with the a's as they're already out of the cabinets. I may not do anything with the c's until the new tubes are ready.

Leland

• http://www.terraworld.net/rentman/Heatsinks

I scrapped the slot idea and just drilled 1/2 holes in the flats, polished a venturi and the interior. There's so much surface area to work with that slots were unnecessary. I have more exit volume than the original opening. You can feel the air pumping out at low frequencies.

There are lots of signal generators for PC sound cards. Do a search on the internet and you'll find a bunch of them. Anything that makes a sine and lets you set frequency will work.