Bastanis Prometheus Speakers

This webpage describes the construction of a pair of Bastanis Prometheus speakers, summer 2016.

The Bastanis are high efficiency (100db) dipole speakers, where the special full-range driver is run full range (no crossover components between the amp and the driver), and the high end is supplemented by a compression tweeter, with an amplified woofer below 100 Hz.

The Bastanis website is here:

The Prometheus speakers are no longer in the Bastanis lineup, but are reviewed here (in the Mk 2 version):
and here:

I purchased the speakers used, partially complete, missing the tweeters and with cabinets in poor shape. I purchased a new tweeter from the former US distributor to complete the system, then built new cabinets, per the Bastanis Prometheus plans, documented below.

Above: The main panels are 3/4 inch baltic birch plywood laminated with 1/2" mdf (as shown above). I veneered the panel faces with cherry veneer, and added solid cherry stock around the perimeter to add strength.  Above shows one of the sides being attached with biscuit joints. 

Above: The main panels assembled (before routing the tweeter cutout), before staining the cherry veneer.  The 12" full range driver cutout is bevelled 45 degrees per the Bastani plans, and since I used 1.25" thick panels (versus the stock 1" panels), I routed the back of the panel so the driver sits in the correct position relative to the front of the panel.  I also routed that circular cutout for a second driver, as in the Bastanis Mandalas, to allow adding a second wide range driver in the future.

Above: Back side of the panel showing the ribs with captive T-nuts for attaching the panel to the woofer box.

Above: Layout of the woofer box showing the driver position. 

Above: Woofer cabinet under construction.  There is a separate sealed enclosure to the left where the woofer plate amp will be mounted.  The open side panel will hold the 12" woofer.  I used the larger of the two suggested box sizes, per Robert Bastani's recommendation.

Above: Woofer cabinets assembled and main panels being finished (cherry stain and polyurethane finish).

Above: Woofer panels being pained cobalt blue.

Above: Completed woofer, with plate amp being mounted.

Above: Woofer cabinet bolted to the main front panel, woofer being prepped for installation.

Above: Completed system with all the drivers mounted.  The "horn" for the compression tweeter was routed directly into the main panel, resulting in a cleaner look.

Above: Completed system with the grills in place.

Above: closeup of the crossover - just a single cap for the tweeter (1uf bypassed with a 0.022uf), and a 12 ohm resistor across the wide range driver.  In the lower left you can see the rear of the tweeter driver.

Above: Side view of the system, showing the dipole panel attached to the woofer box.  The 12" woofers are side mounted as seen here.

Above: Rear view of the speakers, showing the plate amps at the back of the woofer boxes.  You can also see the circular routing on the main panels just above the woofer box, providing a starting point for mounting an optional second wide band driver in the future.