What is phase shift?
Phase is the timing of a signal,
and the shift is the degree of the delay that occurs on the signal when passed through a crossover.
Each order of crossover introduces a 90 degree phase shift.
A 180 degree shift is an inverse of the wave.
If 2 speakers are 180 degrees out of phase
then they will cancel each other wherever they produce the same frequencies.
Even with crossovers,
both speakers will produce sound for several octaves beyond the crossover point.
If this problem occurs, there will be a noticeable dip in the frequency response at the crossover point.
To solve this problem, wire one, but not both, of the speakers backwards (+ to -).
Usually, phase shift problems only occur with 2nd order (or 6th order) crossovers, (หมายเหตุ หมายถึง การใช้ ออร์เดอร์ที่สอง ทั้งเสียงทุ้มและเสียงแหลม
เฟสจะเลื่่อนไปจากจุดตัด คือเลื่อนลงทางเสียงทุ้มและเลื่อนขึ้นทางเสียงแหลม = -90 , +90 = 180 องศา)
but can also occur when using multiple 2-way crossovers in a 3-way (or more) speaker system.
The only way to really find and fix a phase shift problem is trying all possibilities in reversing the speaker leads.
If reversing the leads makes the system sound louder,
then you know you have fixed the problem.
http://www.diyaudioandvideo.com/FAQ/Crossover/
