- 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:
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).
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) :