One-eyed brothers is kit series made of Eminence Beta 8", 10" and 12" co-axial speakers. Samu Saurama(chief editor of HIFI magazine and long term speaker designer) had three goals when he started to this design project: good overall sound quality, good bass and moderate low costs of parts.

You can read original article here (in finnish).

Eminence is one of the biggest speaker manufacturers in world. They can design and manufacture very good speakers for a very good price, because of high volumes. Eminence is known for great PA and instrument speakers but some of their speakers are also well suited for HIFI. Beta range is one of those.

Samu Saurama designed 3 versions but honestly, 12" is clearly the best, so it does not make much sense to build 8" or 10", unless size is all that matters.

So in this article we build 12" model.


Eminence Beta-12CX needs about 100l enclosure in bass reflex design. Prototype size is 370 (width) x 600 (height) x 500mm (depth) , but you can change dimensions as long as the total internal volume is ABOUT 100l (+/- 10% is fine). Please note that all items inside box (speaker, crossover, bassreflex) reduces internal volume.

Beta 12CX overall diameter is 305.6mm, but please, always check all measurements from the speaker and other parts, not from online sources. There might be a 1mm tolerance or so.


Speaker boxes needs some damping. 500g/m2 material is good and recommended is to add:

  • 200mm to bottom and top panels or if there is not 200mm space to fill (until you reach tubes) just put as much as possible
  • 100mm to back panels
  • 50mm to side panels
  • Frontplate does not need any
  • Do not put any material to block bass-reflex tubes: we do not want to block the airflow

So basically you need about 2000 x 1500 x 25mm per speaker if you use this material.


Crossover is quite simple, since these drivers in this box design do not need additional correction.

Download BOM - Bill of materials - here.