About a Nelson Pass phase coherent crossover

[gaetan8888]

Hello

I did found a nice active crossover plan in the document; Phase coherent crossover networks, by Nelson Pass, and it's 2 khz center frequency are righ for me.

I would use the 18 bd / octave schematic.

Is it a butterworth or a bessel type ?

Anybody did a simulation of the summed phase and square wave output on that circuit ?

Thank

Gaetan

An externally hosted image should be here but it was not working when we last tested it.

 

[jackinnj]

Here's a sim, the center plot is the summed magnitude or phase:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[gaetan8888]

Hello

That's look quite good and phase coherent.

Which simulator did you use ?


Thank you very much

Gaetan

 

[jackinnj]

Multisim -- now that National Instruments has taken over it doesn't crash and burn -- EWB was a Canadian company I believe.

Here's the 18dB/8vo

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Nelson Pass]

I should point out that 1 Megohm resistors in the voltage
divider are unrealistically high values for op amps.

Also, it's a lot easier to realize these with ordinary Sallen-Key
filters than with cascaded values of passive components. Just
build the desired filter and use a differential amplifier comparing
the input and output, scaling for gain differences in the pass band.

😎

 

[Nikolas Ojala]

Possible applications for phase coherent crossovers

I think that a WAW (Woofer Assisted Wideband) would be kind of a natural application for a phase coherent crossover. A coaxial speaker driver would be another, perhaps even more obvious. I would be also tempted to use current drive for both the widerange and the woofer.

 

[Lingwendil]

Yep. a fullrange top with a helper woofer is a great application for most of these sorts of phase-coherent electronic crossovers, since you are likely to cross pretty low, time alignment tends to be a non-issue, and biamping makes matching different driver sensitivities a breeze.

coax may need time alignment, or it may not. depends on the actual application and crossover point.

 

[planet10]

We have used phase coherent, 1st order PLLXOs with many/mpst of out WAW. Driver C-C under quarter wavelength and the phase coherence of the XO means that little to none of what a good FR does gets lost. I will be getting a B4 kit when they come and will wire it up as 1st order, meaning i know longer have to worry about amp input impedances.

dave

 

[adason]

Or just put two buffers on the output of your PLLXO now, no waiting 🙂

 

[Nelson Pass]

Written a long time ago, the piece should have identified the distinction
between "phase perfect" and "phase coherent".

My bad.

The circuits in the article are phase perfect in that they sum to form
a perfect replica of the original amplitude and phase, so they do a
perfect square wave.

Phase coherent means that there is a constant phase difference
between the two outputs.

You can make a phase perfect crossover which is not phase coherent.

You can make a phase coherent crossover which is not phase perfect.