Dave Rat on Main PA vs Monitor Polarity

all right I'm Dave rat and today I'm gonna talk about weather of main PA system and a monitor system should be in polarity or out of polarity with each other the reason this question comes up is when you hit a kick drum and if all your systems wired in polarity everything's wired correct positive pressure wave on the microphone diaphragm moves in travels through all the electronics shows up at the amp red terminal creates a positive pressure wave hooks up to the speaker positive pressure with speaker moves outward out of the box well you got your main PA if the kick drum boom boom boom all the speakers are moving out towards the audience and you've got your monitor system running the kick drum into the monitor wedge boom boom boom it's moving towards the band the thing is monitor wedges are point of the opposite direction than the main PA so the main PA speakers are moving out the monitor speakers are moving out the opposite direction that would appear to be logically an outer polarity scenario and that's true it is they are moving in opposite direction in relation to each other and if we used open back speaker cabinets for the main PA and the and/or the monitor system then you could have you could take two speakers wire them in polarity and they would both move out together or you could turn one around backwards and if they're both in polarity wired in polarity they would do this see why I wanted mounted polarity and you can have one in reverse but we're not using figure eight for the most part flat some flat panel systems do have a figure eight polar pattern for the most part we using sealed and/or ported enclosures typically ported enclosures and a ported enclosure or a sealed enclosure basically captures the sound coming from the back of the speaker and keeps it inside the enclosure doesn't let it out so the only thing that escapes a speaker is the sound on the front sound from the front when the speaker moves out with that pulse it creates a positive pressure wave in the very low frequencies that positive pressure wave travels in all directions 360 like a spherical thing it was floating in space there'd be a sphere a positive pressure wave sphere that would radiate from that a ported enclosures basically a sealed enclosure with a little hole in it or a big hole in it and the way those properly designed ported enclosure works is it takes the internal volume or whatever size it is speaker cabinet speaker combination and it starts to roll off at a certain low frequency and then you put a hole in it with a duct on it and that's a tuned resonator called the Helmholtz resonator such that it has output takes that rear that outer polarity rear of the speaker and time delays it and resonates about a hundred eighty degrees out of polarity with the already outer polarity so now it's 360 degrees out of polarity or out of phase shifted which back in the polarity and it puts it out over a narrow band such that the output of the speaker might look like this the output of the port might look like this and the output of the speaker important combination may look something like that giving you an extra low-end boost but for all practical purposes it's an in polarity scenario the entire box works together to output in polarity spherical somewhat directional at the higher frequencies obviously let's go ahead and test that so here we got time to the wedge this is a sealed enclosure and we've got our main PA which is a ported enclosure supported in the rear there and I've got a switcher hear this sound tools mic switcher has on the a input it's got the pink noise in polarity and on the B input it's out of polarity and that's driving the wedge here so I have the ability to switch the polarity on the wedge let's go ahead this is [Music] but in clarity [Music] how to polarity so as you can see hopefully here that the doesn't matter which way this wedge is pointing we're getting low-frequency some ancient and when it's out of polarity we're getting cancellation regardless of the directions pointed I've done shows where we've put the monitor system out of polarity intentionally with the main PA in order to help cancel out some of the low-end by putting extra low in the wedges and things not moving around too much you can cancel some of the low-end on stage by reversing polarity the monitor rig I don't recommend it in many situations it's quite unwieldy because as you bring various low frequency things up or down or if the front of house engineer starts to turn the bass or kick up and down that cancellation no changes so they might turn the kick down in the main PA and you get more low-end on stage because you have kick boosted on the stage to cancel it out but it's something you can try if worse comes to worse all right oh no maybe a monitor system in polarity is the way to go and I hope that's informative and helpful you

Channel: fohtv

Views: 516

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Id: d_3NOvt-gNg

Length: 6min 57sec (417 seconds)

Published: Tue May 19 2020