Ortho Acoustic WAW, update 2.

This is a quick update after some initial simulations. I was planning to try out Rod Elliott's P48a but I would have to redesign it because I will need a full range output with level adjustments. I took inspiration from several of Rod Elliott's designs, like P81 for the LP and P197 for the HP and LF boost. Other inspirations was P107 for the improved phase inversion and the output buffers from P09.

This is my first cut, quite far from the original P48a (please take the output part with a grain of salt because I am still working on this circuit). This is what it looks like in TINA-TI (click the image for higher resolution):

I used VituixCAD to come up with suitable component values. I added buffers (amplifiers) to each element to enable overall positive and negative gain (mainly simulating the output buffer from P09). I then added a Gain EQ to simulate the bass boost stage from P197 and a second order LR to simulate the LP from P81. I used the near field measured response for the elements and started to fiddle around with different filter frequencies and Q values.

I was aiming for an extended bass response down to 30 Hz without an excessive need for power (like a Linkwitz transform without a HP would require). What I ended up with was Gain EQ with a center frequency of 30 Hz and a Q of 2 (representing a gain of x2.5 or 10 dB). In combination with a crossover frequency of 50 Hz for the second order LR. The FR element is attenuated 6 dB. It would give me the following simulated response:

I then had to translate the frequencies and Q into sane component values taking input resistance into account for the phase inverting input buffer from P107 and the variable output buffer from P09. This is the simulated AC transfer using the values above in TINA-TI:

It correspond quite well to the simulation in VituixCAD. Some 10 dB up at 30 Hz and unity gain around 67 Hz. Note that this is me trying to do as little as possible to reach a specific goal. It is designed for my equipment, I got a preamp with variable gain so I don't need variable gain for the sub-woofer like in P48a. I am not sure what power amps I am going to use with this filter but I guess I will have to attenuate the FR branch. I could therefor probably do without the 6 dB gain on the output buffer but I kept it just in case.