The “Blackbird” 3-way speaker components are based on Tony Gee’s “Mezzo Galactica”. I used the same Seas Excel T29CF001-E0038, the same PHL 1130 but, because of availability, I had to use Ciare’s NDH 15-4 instead of the NDH15-3. I also used the same crossover design. I have been careful to make the crossover reasonably easy to remove for adjustments. The “Blackbird” cabinet design is completely different, another reason I will have to make adjustments to the crossover. I have settled on a cabinet design I like but I am not sure how the woofer will perform in the cabinet. I have kept the internal volumes the same as the “Mezzo Galactica” but the woofer cabinet is narrower than the 15″ woofer driver so I constructed a “tear drop” shape to the cabinet sides to accommodate the woofer and I pushed the tweeter up out of the top of the cabinet in another tear drop shape. I did a mock-up using 1/4″ foam core. I laminated 2 sheets of 3/4″ mdf, using wood flooring adhesive, to make panels 1 1/2″ thick, to construct the cabinet. The front baffle is consrtucted of 2 of these panels making it 3″ thick. Wood flooring adhesive has excellent adhesion but doesn’t dry brittle hard, it must stay flexible to allow wood floors to move and I think it will help to kill cabinet resonances. After the panels have dried overnight, I cut them to size and layout the internal bracing. Next the panels are routed for the bracing. This will make the cabinet much stronger than just glueing the braces on the surface. The slots are just deep enough to give a good glueing surface, about 1/4″. The slots shouldn’t pass the glue line of the laminated panels or vibrations could be carried to the outer panel. The bracing is cut, all the corners rounded over and glued into place. With the top and bottom in place it’s time to glue in some triangular pieces into the midrange cabinet. Only the left and right sides are parallel but making the interior irregular should help to break down standing waves and minimize the amount of delayed energy that can be reflected off the rear walls.
Next I applied the adhesive for the second layer of the front baffle. I used screws to secure the outer baffle but removed them after the adhesive dried so there would be no mechanical connection between the first and second layers of the baffle. The tear drop ready for glue-up. Both the tweeter and woofer “tear drops” have been applied using epoxy. I also used a hand plane to round over the baffle edges above the woofer. These cabinets are going to be painted so they need to be completely covered with filler. If only the seams or screw holes are filled it is impossible to get that area to blend invisibly. I use a lightweight body filler, sand and prime. Then I go over the cabinets again and spot fill any pin holes etc., sand and prime again. All this is done in a well ventilated area. I wear a mask and my sander connects to a vacuum. The cabinets have been routed for the drivers and are ready for primer.
Sherwin Williams Black Primer Surfacer. The perfect base for a low sheen top coat.
The interior of the cabinet is lined with 1/2″ felt. The cabinet bottom is filled with sheep’s wool as is the midrange cabinet. Sheep’s wool will also be placed at the back around the ports.
More to come….