I’ve had the parts on hand for this upgrade for over two years but haven’t had the time to execute it until recently. My initial thought was to go external but, after considering various options, took a more invasive approach.
The factory crossover is mounted on a small Masonite plate that attaches to the rear of the speaker. The crossover cavity is open to the front and covered by what looks like open weave black grill cloth:
With a little bit of persuasion, the old crossover and connected terminal plate can be removed more or less intact. This way, should I ever decide to sell these, a new owner has the option to undo the mods (though I can’t imagine they’d want to).
I cut a piece of 6 mm baltic birch ply 7-1/2” high x 16-3/4 wide to mount the new components, painted the front face flat black, and traced the outline of the crossover cavity on the back. There’s plenty of room on the front of the speaker to mount this panel with screws at all four corners. I laid out the components to get the maximum distance between the coils. By putting the smaller coil in the area where the old terminals connected, I got almost 8” spacing between coil centers. The control cavity is 1-1/2” deep, which is not enough to flush mount the female tube connectors and allow for a gentle bend of the 14ga input wires. I made a new plate to the same dimensions as the original out of 6 mm ply and glued on a small block of ½” MDF to raise the tube connector mounts. Keeping connector bodies out of the cavity gave me more space to accommodate the small coil.
Here's the wired crossover/input terminal prior to installation:
And here’s what the business end looks like after reattaching the grill sock and trim:
First listening impressions are snappier transients and more inner detail, e.g., when listening to vocal harmony you get the blend but can also pinpoint individual voices.
