Towards a complete Linn Kaber Aktiv solution using an rPi and AV receiv

[oomzay]

I thought I'd share my journey towards a Linn Kaber "Aktiv" solution using CamillaDsp for the crossover and an off-the-shelf AV receiver as the multichannel amplifier. This will hopefully work with any beefy AV receiver with HDMI input and a direct/pure multichannel mode. But be warned - the AV receiver must be dedicated to this application. Selecting an unfiltered multichannel source or engaging the receiver's fancy effects modes will likely blow your tweeters! I will be keeping a capacitor inline with the tweeters as insurance.

I am new to x-over design so please pile in with any tips and hints. Hopefully this will lead somewhere that is useful to others wanting to drive active speakers on a budget!

A little background

I have owned two pairs of kabers since 2007 when I bought them very cheaply (~£125 a pair) and was going to use them for AV surround. In the event this didn't work out so they have only had part time jobs ever since. One is factory passive and the other is factory aktiv - but it came with passive x-over boards which I fitted into an external box - which is now proving very handy...

My eureka moment was when I realised that with camillaDSP/rPi I could feed all 6 (2 x 3) filtered channels over an HDMI cable to an AV receiver by pretending they were 2 x Front, 2 x Side and 2 x Rear channels, which seems rather obvious now!

Progress so far

• Passive stereo over HDMI - Trivial
  
• Passive Tri-amped - Stereo mixed to 2 x 3 channels - !!! MASSIVE IMPROVEMENT !!! - could just stop here!
  
• Active Tri-amped - proof of concept - Simple x-overs 80Hz LR2 & 2800Hz LR4 - Doesn't sound great but !!! THE CONCEPT WORKS !!!
  
• Search, beg or borrow an existing Linn Kaber DSP x-over  pipeline - No luck with this!
  

Future

• Check I am really getting 24bits over the HDMI? (How?)
  
• Get to grips with speaker measurement tools. (REW and friends?)
  
• Design and tune DSP kaber x-overs.
  
• Add room EQ to DSP pipeline.
  
• Optimise rPi boot time? (rPi is powered   from the AV switched socket)
  
• Write-protect the rPi. 
  
• Investigate ways to publish and qualify speaker x-overs pipelines with community/moOde
  
• ...