Audi H-Baffle Hybrid ESL

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!