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Three-Way Coaxial Speakers

Design Goals

I intend these speakers to be the last big speaker build in my life, so I want to do them right :)

  • Full range living room speaker for normal listening levels in flats (not exceedingly loud).
  • Coaxial speaker design for coherent sound reproduction. Chosen driver: Thiel SCS4.
  • Wide baffle (~60cm) with large rounded corners (r>5cm) for minimizing baffle step problems and more even off-axis frequency response.
  • Closed box design. In my experience easier to set up in a room than ported designs and the bass response is easily accounted for by some low shelf eq boost.
  • Actively crossed over and equalized (see above) with Pulseaudio Crossover Rack and multi-amped with modern class-D amps.

Progress (blog-style, in reverse order)


  • Thiel SCS4 Speakers are here. I disassembled one to get the driver out and cut the aluminium front baffle to size.
  • I bought two plates of granit 146x40x3cm which will become the new front baffle and maybe the rear baffle of the woofer compartment. These will be cut and routed by a special company near here. I'm currently drawing up the CAD, please see the pictures
  • For the woofer chassis I decided to use the Alcone AC 10 HE aluminium cone.
  • I'm searching for cheap supply of plywood. The side and top baffles will be made of soild birch plywood and i calculated that I roughly need about 10m2 for both speaker enclosures.
  • A preliminary crossover config was made in Pulseaudio Crossover Rack, the config can be seen in the images below.
  • Finally some pictures: