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  fEARful: MX21's bi-amp information

  1. MX21's 1212/6 Build
  2. one full-range speakon & one bi-amp speakon
  3. one full-range or LF speakon & one HF speakon
  4. one speakon (or two) doing all
  5. the "one speakon doing all" approach finished
  6. custom speakon cable


MX21's 1212/6 Build

To switch between my fEARful 1212/6 internal passive "Cheap-But-Good" (CBG) crossover and an external bi-amp active crossover, I used a 4-pole double-throw (4PDT) switch. The 4 poles completely isolate the internal crossover when switched to the bi-amp position. I used a 4PDT switch with spade terminals:

Mouser All Products » Electromechanical » Switches » Toggle Switches » S42F-RO

There are several ways to configure your connectors for full range or bi-amp inputs from your amp. Following are some passive/bi-amp connection approaches.



one full-range speakon & one bi-amp speakon

Bi-amp with 2 speakon connectors. 1 speakon is for full range input to the passive crossover, the 2nd speakon is for bi-amp with 1+/1- for the low frequency input and 2+/2- for the high frequency input. Switch up for passive, down for bi-amp.



one full-range or LF speakon & one HF speakon

Bi-amp with 2 speakon connectors. With the switch in the bi-amp position (down), speakon 1 1+/1- is for the low frequency input and speakon 2 1+/1- is for the high frequency input. With the switch in the passive position (up), speakon 1 1+/1- is the full range input.



one speakon (or two) doing all

Bi-amp with 1 speakon connector. With the switch in bi-amp position (down), speakon 1+/1- for the low frequency input and 2+/2- for the high frequency input. With the switch in passive position (up), speakon 1+/1- is full range input to the passive crossover.

optional: ghosted in is parallel connections leading from the speakon to a second speakon, to be used for "daisy chaining" enclosures - greenboy



the "one speakon doing all" approach finished

Here's what my completed connector cup connections between speakon, crossover, and 4PDT bi-amp switch hookup looks like:




custom speakon cable

I also built a custom bi-amp speakon cable. The dual-speakon Y features two 2-conductor speakons wired 1+/1-. One of those is for lowpass coming of an amplifier channel and the other speakon is for the highpass coming off the other amplifier channel. At the other end is a 4-conductor speakon wired 1+/1- from the LF speakon and 2+/2- from the HF speakon. This goes into the fEARful connector cup jack.


                                              _______ 1+   2-pole    power amp
                              1+ ____________/  _____ 1-  speakon    channel A
           fEARful    4-pole  1- ______________/
          enclosure  speakon  2+ ______________
                              2- ____________  \_____ 1+   2-pole    power amp
                                             \_______ 1-  speakon    channel B

Note1: The CBG passive crossover wires the midrange in reverse polarity to that of the woofers. For bi-amp, the mid+ and mid- go to the 2+ and 2- pins of the speakon respectively. I can do any polarity reversals as needed with the external active crossover.

Note2: Two Neutrik speakon jacks can be put next to each other on the enclosure's connector cup and wired in parallel to supply a pass through signal for "daisy-chaining" to a second fEARful that is wired identically.



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