What exactly does the "polarity" button do on the JBL PRX 718 sub?

[sickman]

I can hear a difference when I push the cross over button in/out, but I don't notice a change with the polarity button. Should it be out or in? What is it's function?

[Coaster]

it reverses the polarity. use it or not depending on your tops; as well as slopes and types of xover filters.

[Craig Vecchione]

An extreme example of when you would use the polarity button is if you (for who knows what reason) were forced to set up the subs on opposite sides of the room facing each other. In this case, the subs would cancel each other at the center, and you'd have gradually increasing levels as you moved to one side or the other. By engaging just one polarity switch on either of the subs, they would reinforce each other instead of cancel each other.

[karlw]

 

An extreme example of when you would use the polarity button is if you (for who knows what reason) were forced to set up the subs on opposite sides of the room facing each other. In this case, the subs would cancel each other at the center, and you'd have gradually increasing levels as you moved to one side or the other. By engaging just one polarity switch on either of the subs, they would reinforce each other instead of cancel each other.

 

 

I just want to make the point that normally, if both subs are in phase, they could be on opposite sides of the room, facing each other, and they would not cancel each other out. Think of a positive signal going to both subs. They both push air towards the center of the room. From the listener's point of view, at the center of the room, plenty of signal would be heard. In fact, it would be 3dB more than with just one sub.

 

Now, in that same exact setup, if you were to engage the polarity switch on ONE of the subs, then you would get the situation you described: you would have cancellation in the center of the room.

 

To the OP: normally, it is very difficult or near impossible to hear absolute polarity on most signals. But when your sub is combined with other cabinets, then the polarity matters because you may have cancellation at overlapping frequencies (where the tops and subs cover the upper bass, as an example) resulting in crappy sound.

[Coaster]

put down the bong craig.

[modulusman]

I can hear a difference when I push the cross over button in/out, but I don't notice a change with the polarity button. Should it be out or in? What is it's function?

 

If you are using only one sub I don't think it matters if it is in or out.

[RoadRanger]

If you are using only one sub I don't think it matters if it is in or out.

Being in or out of phase with the mains should make a difference.

[Harmonycat]

I can hear a difference when I push the cross over button in/out, but I don't notice a change with the polarity button. Should it be out or in? What is it's function?

 

It is a lot more convenient than switching the wires on one sub.

 

That's how we did in the old days.:poke:

[dboomer]

The simple answer is hook up the system and play something with a fair amount of bass, flip the switch and keep it where you hear the most bass.

 

First do it with only one sub to one top and then pair to pair.

[Craig Vecchione]

 

I just want to make the point that normally, if both subs are in phase, they could be on opposite sides of the room, facing each other, and they would not cancel each other out. Think of a positive signal going to both subs. They both push air towards the center of the room. From the listener's point of view, at the center of the room, plenty of signal would be heard. In fact, it would be 3dB more than with just one sub. Now, in that same exact setup, if you were to engage the polarity switch on ONE of the subs, then you would get the situation you described: you would have cancellation in the center of the room. To the OP: normally, it is very difficult or near impossible to hear absolute polarity on most signals. But when your sub is combined with other cabinets, then the polarity matters because you may have cancellation at overlapping frequencies (where the tops and subs cover the upper bass, as an example) resulting in crappy sound.

 

 

In-phase signals reinforce, they don't cancel. Constructive vs destructive interference. While you do have plenty of signal as you stated, your audio perception is that there's a drop in volume at the center. At any place between the out of phase pair, the closer speaker is being cancelled by the further to a greater degree as you move away from the former.

 

I've tested this after positively verifying phase in the system, and the center is noticeably reduced in volume. It also sounds phasey and weird as you turn your head. Reversing one speaker's phase results in even sound from one speaker to the other. It might not have a peak, but it also doesn't have the noticeable drop in the center.

[agedhorse]

 

Being in or out of phase with the mains should make a difference.

 

 

Or not.

 

W/ 24dB/octave xover filters there's enough band rejection that it doesn't matter in most cases. It's not like signal.

[sickman]

 

The simple answer is hook up the system and play something with a fair amount of bass, flip the switch and keep it where you hear the most bass. First do it with only one sub to one top and then pair to pair.

 

 

I only have one sub. I played some Dr. Dre and Audioslave stuff, both of which are more bass heavy than anything I am currently playing with a band. I could definitely tell when the x-over button was in/out, but not the polarity button.

 

From reading what you guys have posted if I have the sub under one of the mains it is not going to make much of a difference.. is this correct? I have read some posts about bands using one sub and putting it by the drummer or bassist, shouldn't it be in front of the band? It seems like if it was in back it would force the band to turn up on stage.

 

My plan is to get a pair of speaker sticks and either put the sub center stage or on either the right/left side against a wall on the front of the "stage" if we are in a corner. Does this make sense?

 

Thanks.

[RoadRanger]

My plan is to get a pair of speaker sticks and either put the sub center stage or on either the right/left side against a wall on the front of the "stage" if we are in a corner. Does this make sense?

Sure . BTW you might find that the kick mic feeds back less in one polarity or the other so that might be a good reason to play with it - but it's going to be different with different rooms and placement. I often have the subs clustered under one or both of the the mains on one or both sides so kinda think the subs should be in phase with the mains then. I'll agree that if the subs are not with the mains that their "ideal" phase may be different or non-existent.

[dboomer]

 

From reading what you guys have posted if I have the sub under one of the mains it is not going to make much of a difference.. is this correct?

 

 

Maybe, maybe not. It's more likely where it makes a difference. There are real reasons but it all comes down to just leave the switch where it sounds best. If you can't hear a difference then it doesn't matter.

 

It is gonna change the transition from tops to sub. No right or wrong answer in either case. Pick what you like.