Switching polarity of tweeter in two-way design


In order to align the time&phase of the tweeter to the woofer in a two-way design, is it a common practice to switch the polarity of the tweeter so that it is slightly delay in time? It would be similar to having the baffle slanted at a small angle.

I think it is done on the ProAc 2.5 and probably on some of the DIY two way speakers
andy2
As for tilting the baffle to align time and phase of the tweeter to the woofer, does the degree of tilting depends on the x-over only or only on the acoustic characteristic of tweeter itself?
"For real-world listening, polarity of the tweeter does not seem to make a lot of difference. Best idea is to try it both ways."

I don't disagree with that, but understand the effect of reversing the tweeter leads from their original backwards orientation. Reversing the tweeter will create a small up-peak in response in the midrange/tweeter crossover region, this ocurring usually around 2.5KHz. I suppose you'd hear that occasionally as added presence or brightness (or maybe 'detail').

What I don't understand is why the designers don't simply pull the crossover frequencies apart to eliminate the spike. But I guess that simply shows how much I don't know.
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Second order (acoustic) high and low-pass responses are 180 degrees out-of phase.

You get deep notch if you don't invert one (in a perfect world you'd have no output).

Linkwitz Riley filters have Q=.5 with both outputs -6dB at their pole. Inverting one therefore causes the response to sum flat.

2nd order butterworth filters at the same frequency (Q=.707) so you get a 3dB peak when you invert one and combine. Spreading the cross-over frequencies is needed to avoid this.

Sloped baffles accomplish two things:
1. Time alignment of the drivers so the real phase relationship matches theoretical.

2. Having the highest output on-axis rather than off when you don't use a Linkwitz-Riley cross-over.