I call this speaker the “Audi” because it was built for a
friend who needed the speaker pair to fit into his 2008 Audi car for
transporting. This was accomplished using
OB bass to eliminate the woofer boxes. Frame
dimensions are 66” height x 14.5” width, and the H-baffle base is 16” width x
16” depth.
The cab/frame and wire support lattice are red oak finished
with a light stain and clear satin polyurethane. Nice wood, solid joinery and a state of the
art electrostatic driver make this speaker a truly fine musical
instrument. This is the nicest looking easiest
to build of my designs but it’s still a big project; requiring woodworking
skill and at least a table saw, planar and router.
The frame rails are joined with strong finger joints which
eliminate the need for corner bracing. The finger joints were easy to cut on the table
saw using a simple home-made jig found on Youtube. The face/baffle pieces were glued together
using rabbited lap-joints cut on the table saw.
The face/baffle assembly was then clamped and glued to the frame
assembly. The woofer cutout was then cut,
using a router and circle jig. The removable
triangular plywood base pieces are attached with ¼-20 button-head cap screws, screwing
into threaded brass inserts in the frame.
As with all my designs; there is no passive crossover-- this
speaker is bi-amplified using an active crossover upstream of the amps. The narrow baffle’s dipole cancellation physically
limits output in the lower octaves, but the single 12” woofer is adequate to
moderate/normal listening volume. In a 3-way
tri-amp setup, with a pair of subs crossing in around 70Hz, this speaker really
rocks.
The step-up transformers and HV bias supplies are mounted on
the back shelf, under a clear polycarbonate cover. Heat-bending the cover was done with a heat
gun, with the plastic clamped between boards in a vice to form the bend
lines. It took a couple of attempts to
perfect the heat-bending technique but it worked out nicely. The shelf fits into dados in the plywood side
pieces.
Below the panel, a small slide-in shelf houses the
segmentation-resistor network, which is visible under a clear polycarbonate
cover.
The original speaker version shown in the photos used a rear-mounted,
low-Qts Eminence woofer; which isn’t the best choice for OB but makes a more seamless
blend with the ESL in the crossover band—at the expense of requiring more EQ to
balance the bass output. The speaker version
shown in my CAD drawing uses a medium-Qts Peerless SLS woofer, which isn’t
quite as seamless with the ESL but gives good bass output without a lot of EQ,
and it costs about half as much as the Eminence. I would say the Peerless SLS is better in a 2-way
setup without subs and the Eminence is better in a 3-way setup with subs.
Click here to see a video of the new speakers playing at the 2018 Carverfest retreat in NC. Enjoy!
