To be clearer on the sub polarity. When I say match polarity it is not entirely physical but more of "try it both ways and see what sounds best."
Not to go too deep down the RLC/LCR Electrical Engineering rat hole... The crossover (all analog crossovers) will cause phase shift, how and what will depend on the "order" (first order, second order....). There will also be overlap (at the crossover frequency, by design) even if both the sub and mains are running through the same crossover. Even if everything is set up to look correct (physically--wiring wise) at the crossover point there is a chance the mains and the sub are cancelling each other out (one is backwards internally), so it does not hurt to reverse the polarity (to test) just to make sure. Some better subs will have a switch (but not all), some receivers have the option, if not just try reversing the wires on the speakers (all of them, mains, centre and surrounds) just to see.
Generally (ignoring the speaker locations and the impact of the speed of sound...) it is not a problem BUT when you start mixing x, y, and z brands you can run into a problem.
BTW this exact thing is happening in the speakers by design...the crossover (RLC/LCR circuit) in the speakers has phase shift. If the speakers are 2-way it is common for the tweeter to be internally wired reversed from the woofer (to correct for the shift at the crossover point), if not they will cancel each other out at the crossover point (each shifted 90 degrees in opposite directions = 180 degrees, depending on the order...). 3-way speaker the mid is commonly wired backwards (from the woofer and tweeter) for the same reason. Again, will depend a bit on the order of the crossover.
Long story short, what happens if the speaker maker decided to reverse the woofer instead of the tweeter.... without fancy test equipment we can only experiment with our ears as the test equipment. Then we consider the speed of sound and the location of the speakers...
At 100 Hz we are also talking ~2m for a half wavelength (from memory...), this is one of the reasons sub positioning also comes into the polarization equation. For this we use the positioning methods mentioned earlier first and try the above switch after we find the ideal position was found (by rolling around on the floor...). It is not as simple as a distance calculation (sub location) because the sound is bouncing off of the walls, furniture, room gain, etc.
Not to go too deep down the RLC/LCR Electrical Engineering rat hole... The crossover (all analog crossovers) will cause phase shift, how and what will depend on the "order" (first order, second order....). There will also be overlap (at the crossover frequency, by design) even if both the sub and mains are running through the same crossover. Even if everything is set up to look correct (physically--wiring wise) at the crossover point there is a chance the mains and the sub are cancelling each other out (one is backwards internally), so it does not hurt to reverse the polarity (to test) just to make sure. Some better subs will have a switch (but not all), some receivers have the option, if not just try reversing the wires on the speakers (all of them, mains, centre and surrounds) just to see.
Generally (ignoring the speaker locations and the impact of the speed of sound...) it is not a problem BUT when you start mixing x, y, and z brands you can run into a problem.
BTW this exact thing is happening in the speakers by design...the crossover (RLC/LCR circuit) in the speakers has phase shift. If the speakers are 2-way it is common for the tweeter to be internally wired reversed from the woofer (to correct for the shift at the crossover point), if not they will cancel each other out at the crossover point (each shifted 90 degrees in opposite directions = 180 degrees, depending on the order...). 3-way speaker the mid is commonly wired backwards (from the woofer and tweeter) for the same reason. Again, will depend a bit on the order of the crossover.
Long story short, what happens if the speaker maker decided to reverse the woofer instead of the tweeter.... without fancy test equipment we can only experiment with our ears as the test equipment. Then we consider the speed of sound and the location of the speakers...
At 100 Hz we are also talking ~2m for a half wavelength (from memory...), this is one of the reasons sub positioning also comes into the polarization equation. For this we use the positioning methods mentioned earlier first and try the above switch after we find the ideal position was found (by rolling around on the floor...). It is not as simple as a distance calculation (sub location) because the sound is bouncing off of the walls, furniture, room gain, etc.
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