I want to recycle a pair of stout 3/4" plywood cabinets that measure roughly 29"h x 18"w x 14"d. I plan to make a new baffle board by gluing 3/4" plywood to 3/4" MDF, then using a plunge router and circle jig. I calculate the internal volume at ~2.9 cu ft minus some bracing, so about 2.7 cu ft. I penciled a layout with the 15" up from the bottom 3", and the bottom of the horn flange less than 1" from woofer edge. This appears to leave plenty of room for a horiz. brace inside between drivers, and also leaves room for two 3" circular ports (one in each bottom corner).

Questions:

Any tips for gluing two pieces about 27 x 17"?

Is internal volume pretty close to the Four Pi?

Layout is different from Four Pi pictures, with horn smack over the woofer, and ports in bottom corners. Any issues there?

Thanks,
Rick aka tubino

As for the crossover, assuming you'll be using an 8Ω DE250, I suggest adding a little more attenuation to the tweeter circuit. Instead of using 25Ω and 16Ω for R1 and R2, use 30Ω and 14Ω, respectively. This will make up for the difference in voltage sensitivity. When using a 2226J instead of a 2226H, scale all values in the woofer circuit to match, doubling the inductance and resistance values and halving the capacitance values.

I also suggest that you don't skimp on the resistors. They don't cost all that much and even if you're using low-power tube amps, it never hurts to over-rate the parts and keep 'em cool. It also allows you to use your speakers with the full amount of power the drivers are designed for without risking damage to anything. There's a lot of dynamic range potential in a speaker like this, but only if all the parts can handle it.

My tendency would be to use lower wattage on the resistors since my "big" amps (SE 845) are nowhere near 100w, but I think I'll follow your advice. I may be loaning these to a friend who thinks he needs to spend a lot to get good speakers (Stereophile reader!). Knowing they could handle even a big SS amp would provide peace of mind.

Is your crossover board useable with the large inductor values needed for the 16R woofer? To make matters worse, I like the Erse inductors for these large mH values. The Erse are nice for mounting to a free-form board, but maybe not to your PCB...

• Tweeter circuits for constant directivity horns and waveguides