When working with lower-cost drivers, the crossover design is often more difficult than it would be with pricier drivers. Flaws in the drivers must be compensated for, and at the same time an effort must be continuously made to keep the number of components and cost as low as possible. I struggled with the crossover design for quite some time, trying many different topologies to get the desired performance without excess components. In the end, I was able to start with a somewhat more complex crossover, and then carefully eliminate components that were not critical to the design.

The crossover on the woofer portion is a straightforward second order low-pass filter. Initially I used a conjugate network to contour the upper end response, but found that it was not necessary to the overall design, and could be compensated for by adjusting the shunt capacitor value. The upper-end cutoff of the woofer is at about 500 Hz.

The midrange takes over from 500 Hz through about 6,000 Hz, and uses second order high-pass and low-pass filters. A 4 ohm padding resistor reduces the output by several dB, while propping up the impedance throughout the midrange. The piezo tweeter uses a .22 uF capacitor in addition to a fixed L-pad. In this case, the presence of the two resistors is critical to the functioning of the tweeter crossover; without the shunt resistor the high-pass filter would not function correctly. In true vintage style, a variable L-pad could be substituted in place of the fixed resistors if desired.