Since all passive crossovers phase shift the signal i.e. a 6 dB filter shifts 90 degrees and a 12 dB 180 degrees i wonder if anyone tried to shift tweeter polarity to optimise a high freq response.
Any thougths?

Here's an interesting site about the subject:

http://www.customanalogue.com/elsinore/elsinore_19.htm

Any comments?

Hmmmm...

Sometimes a simple "Hmmm" is good enough.....

Here's another interesting article about this intriging subject from one of the best technical heads of our times concerning audio: Mr. Nelson Pass.

"On some filters we find that inverting the output
of the high or low pass filter results in more accurate total
amplitude or phase response...."

http://www.firstwatt.com/downloads/phasecrx.pdf

Yes reversing the phase on the tweeter can make a big difference in 2nd order (12db) and larger x-overs. It is actually a recommended design practise. 1st order the effect is very minor. If you have bi-amplable 2-way speakers it is very simple to test, just reverse the leads to the high end.

Next on my list of speaker projects is a no x-over multi-driver design. Not sure when I'll get to it though. I only do 1st order myself.

Cheers,
Ian

If your xover is designed properly what would be the advantage of doing this? With the right xover you are getting the optimum from all your drivers. I wish I still had my books. Doesn't what tweeter you use also affect the outcome? If you use a slower tweeter then inverting the tweeter would have a minimal effect.
Man you are making me think this early in the morning. I'm doing all this from memory. I have to think on this. I'll be back. Really I would have to hear the difference. I may try it today.

It is just an intriging subject that i'd came across because a friend of mine bought a pair of Kef Q Seriesspeakers and they have have an inverted tweeter polarity. Later i found out that Monitor Audio Studio 2 and the old JBL 4425 monitors also have polarity inverted between drivers. Hence my questions.

Here's also part of an interesting article from Wiki:

"Second order crossovers

2nd order filters have a 40 dB/decade (or 12 dB/octave) slope. 2nd order filters can have a Bessel, Linkwitz-Riley or Butterworth characteristic depending on design choices and the components used. This order is commonly used in passive crossovers as it offers a reasonable balance between complexity, response, and higher frequency driver protection. When designed with time aligned physical placement, these crossovers have a symmetrical polar response, as do all even order crossovers.

It is commonly thought that there will always be a phase difference of 180° between the outputs of a (second order) low-pass filter and a high-pass filter having the same crossover frequency. And so, in a 2-way system, the high-pass section's output is usually connected to the high frequency driver 'inverted', to correct for this phase problem. For passive systems, the tweeter is wired with opposite polarity to the woofer; for active crossovers the high-pass filter's output is inverted. In 3-way systems the mid-range driver or filter is inverted. However, this is generally only true when the speakers have a wide response overlap and the acoustic centers are physically aligned."

It has been so long since I designed a Xover. I have forgotten alot. I never built a xover with resistor in them. A resistor will color the sound you get. Sometimes I want to start building speaker again. But I listen to my Epos with such small drivers that sound so good. So I say why bother.