Bi-Amplification ACTIVE-PASSIVE


 
  • Bi-amplification "Passive":

  • Bi-amplification "Active":

  •  Bi-amplification "Active-Passive":


Low Pass Filters #1 have the same cut-off frequency.

High Pass Filters #2 have the same cut-off frequency.

This way may considerably reduce the "passive" speaker crossover filters (1 and 2)  "work" ( example of 24db/octave if 4th order active filter use) but only outside the corner frequency region. Indeed, the drawback is a little notch at the corner frequency region of about 6db.

This technique would avoid to have to modify the interior electrical connections of your valuable existing speakers...

Note: very important to have speakers with "bi-wiring" connections to avoid damage to amplifiers...

  • Example of frequency curve response with active crossover (2 ways):
     4th order with corner frequency of 2350 HZ to match the frequency of a passive crossover (2 ways) in a real speaker:

Circuit:

 

Response (LPA: Low Pass Active, HPA: high Pass Active, lpp: low pas passive, hpp: high pass passive, lpT: low pass total (active & passive in series), hpT: high pass total (active & passive in series):

  • Preliminary Conclusion:
    Active bi-amplification is most probably better then "active-passive" but again, the latter has the advantage of not modifying your existing valuable speakers...

 

  • Prototype construction:

This is a selectable cut-off frequency (30 choices between 56 Hz to 3200 Hz) and adjustable gain active crossover to be used for any speaker in a 2 ways active system (the third way or more for higher frequency would stay passive as shown above).

  • Modifications:
  • Opamps were OPA134. However, several opamps have been replaced with custom discrete opamps as seen in above prototype picture. These discrete circuits are a Fit Form Function of the 8 pins DIP single op-amp. 2 different schematics are being used:

      • 6 transistors version (Gain = 1.5):

          • 4 transistors version (Gain = 1) :

     

    Ref: Elliott Sound web page on bi-amplication