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[Greg Bart]

Hello all. I work in a small club and I have 2 JBL PRX518's stacked on house left. so in the PA2 I selected the PRX518's as my subs and I have K12.2 for tops. Since the 2 subs are stacked, should I flip the polarity on one of the subs? Also, should I have the crossovers engaged on the subs or let the selected crossover points in the PA2 control the subs. I feel like if I engage the subs crossovers, I get a lot more low end. Thanks all in advance.

[Matthias McCready]

Hello all. I work in a small club and I have 2 JBL PRX518's stacked on house left. so in the PA2 I selected the PRX518's as my subs and I have K12.2 for tops. Since the 2 subs are stacked, should I flip the polarity on one of the subs? Also, should I have the crossovers engaged on the subs or let the selected crossover points in the PA2 control the subs. I feel like if I engage the subs crossovers, I get a lot more low end. Thanks all in advance.

Hello Greg,

For flipping the polarity - short answer, no.

Slightly longer answer, not unless you are looking to do a cardioid deployment, but there a bit more to that than just hitting the polarity button on one - this thread may assist in your learning but that usually involves more than 2 subs, requires some space behind them, and will not feel quite as tight - probably not the best move with two.

For crossover - that is your hand-off point between your mains and subs. It is important that your tops and mains be in phase (time) at this point, otherwise you will end up with cancellation at that frequency area, rather than summation.

Phase can be shifted by adding delay to align your sub(s) and top(s) - although you only get to pick one place in the room for that relationship to be "perfect."

Crossover filters, in their nature, muck with the phase quite a bit - which can potentially make matching the phase of your tops and subs difficult - although sometimes they can help - this is where transfer functions come in handy. 

Using two crossovers filters can make matching things up extremely difficult - so make sure you are not doubling up.

Also for crossovers, keep in mind that there are actually two:

1) Your set crossover - the one in your DSP (example: 60hz, or 80hz)
2) Your acoustical crossover - this is your true crossover, it is the frequency where the tops are physically louder than the sub - and this is dependent on how loud your sub(s) are or more practically how many subs you have. In short more volume shifts the crossover point up.

---

Clearly, you are curious about the system you are working on, what are you trying to get out of it that you are not currently?

Before making any serious tweaks, two pieces of advice:

1. Save the current preset and backup that up somewhere else, and/or write down all of the settings before you change any - when I am working on systems I like to "do no harm," worst case scenerio you want to be able to get back to your starting place.  I have certainly been called to venues because someone deleted the file or started making tweaks to an install - which can be expensive for the client.
2. It might be a real good idea to invest in a measurement setup (or to borrow one from a friend) - that will give you objective data to correlate with what you are hearing. 

MATH

[Steve-White]

^^^ That.

[Greg Bart]

Hello Greg,

For flipping the polarity - short answer, no.

Slightly longer answer, not unless you are looking to do a cardioid deployment, but there a bit more to that than just hitting the polarity button on one - this thread may assist in your learning but that usually involves more than 2 subs, requires some space behind them, and will not feel quite as tight - probably not the best move with two.

For crossover - that is your hand-off point between your mains and subs. It is important that your tops and mains be in phase (time) at this point, otherwise you will end up with cancellation at that frequency area, rather than summation.

Phase can be shifted by adding delay to align your sub(s) and top(s) - although you only get to pick one place in the room for that relationship to be "perfect."

Crossover filters, in their nature, muck with the phase quite a bit - which can potentially make matching the phase of your tops and subs difficult - although sometimes they can help - this is where transfer functions come in handy. 

Using two crossovers filters can make matching things up extremely difficult - so make sure you are not doubling up.

Also for crossovers, keep in mind that there are actually two:

1) Your set crossover - the one in your DSP (example: 60hz, or 80hz)
2) Your acoustical crossover - this is your true crossover, it is the frequency where the tops are physically louder than the sub - and this is dependent on how loud your sub(s) are or more practically how many subs you have. In short more volume shifts the crossover point up.

---

Clearly, you are curious about the system you are working on, what are you trying to get out of it that you are not currently?

Before making any serious tweaks, two pieces of advice:

1. Save the current preset and backup that up somewhere else, and/or write down all of the settings before you change any - when I am working on systems I like to "do no harm," worst case scenerio you want to be able to get back to your starting place.  I have certainly been called to venues because someone deleted the file or started making tweaks to an install - which can be expensive for the client.
2. It might be a real good idea to invest in a measurement setup (or to borrow one from a friend) - that will give you objective data to correlate with what you are hearing. 

MATH
Hey Mttthias, thank you for all the advice.  I've got someone with SMAART and will ask him to com in and Analyze the room. Another thing. Ive got the stacked subs running in "mono" Should I put them in "stereo"? Thank you again. -Greg

[Matthias McCready]

MATH
Hey Mttthias, thank you for all the advice.  I've got someone with SMAART and will ask him to com in and Analyze the room. Another thing. Ive got the stacked subs running in "mono" Should I put them in "stereo"? Thank you again. -Greg

No keep them in mono.

Why?

1. They are in one place in the room, not two.
2. Even if they were separated - bass is omni-directional - while localization is not - you would still not be gaining anything.
3. The benefit of having your subs together, as you do, is you get some coupling gain - part of that coupling is that they are doing the same thing - if they are doing different things, you could lose that. :-)
4. Most bass in recorded music is mono, and if you are mixing it, you are probably/hopefully mixing the bass in mono. :-)

[Tim McCulloch]

No keep them in mono.

Why?

1. They are in one place in the room, not two.
2. Even if they were separated - bass is omni-directional - while localization is not - you would still not be gaining anything.
3. The benefit of having your subs together, as you do, is you get some coupling gain - part of that coupling is that they are doing the same thing - if they are doing different things, you could lose that. :-)
4. Most bass in recorded music is mono, and if you are mixing it, you are probably/hopefully mixing the bass in mono. :-)

There is a double serving of It Depends ice cream for everyone!

The spatial placement of the subwoofer(s) relative to walls or other boundary surfaces determines the perceived performance at different listening positions in the room.  The geometry of the room, the size and ratio, determine what frequency response will be like at any given place.  It gets really complicated in 3D. edit ps: experiment! Science project time!  One sub, on a castor board, a long cable, and pink noise.  Decide where you want the listening point to be, bring up the noise (the funk comes later) and have a friend move the sub around - closer, further to walls, corners, large obstructions, have some spots spike marked, and listen.  Bonus points if you put up the spectrum analyzer of your choice that can do real time waterfall display.  Now switch places with your buddy, do the course again and listen to what it sounds like where the subwoofer is...

Correcting subwoofer "stuff" with electronics?  The question to be answered - what is responsible for the *sound* of the subwoofer?  You have 2 tools, time and magnitude.  Choose wisely, Young Padawan.

[Greg Bart]

There is a double serving of It Depends ice cream for everyone!

The spatial placement of the subwoofer(s) relative to walls or other boundary surfaces determines the perceived performance at different listening positions in the room.  The geometry of the room, the size and ratio, determine what frequency response will be like at any given place.  It gets really complicated in 3D. edit ps: experiment! Science project time!  One sub, on a castor board, a long cable, and pink noise.  Decide where you want the listening point to be, bring up the noise (the funk comes later) and have a friend move the sub around - closer, further to walls, corners, large obstructions, have some spots spike marked, and listen.  Bonus points if you put up the spectrum analyzer of your choice that can do real time waterfall display.  Now switch places with your buddy, do the course again and listen to what it sounds like where the subwoofer is...

Correcting subwoofer "stuff" with electronics?  The question to be answered - what is responsible for the *sound* of the subwoofer?  You have 2 tools, time and magnitude.  Choose wisely, Young Padawan.

Thank you Tim. Unfortunatly my subs need to be where they are at. The club ir fairly small with a wll on the house right side. I had the subs on house right stacked, but too much low end was bleeding ont the stage, so I moved the stack to house left and it stopped the low end bleeding to the stage. I don't think PRX518's can be placed in cardioid position. Anyways, I've got somone with SMAART and will do some traces. Thank you again. -Greg

[Greg Bart]

No keep them in mono.

Why?

1. They are in one place in the room, not two.
2. Even if they were separated - bass is omni-directional - while localization is not - you would still not be gaining anything.
3. The benefit of having your subs together, as you do, is you get some coupling gain - part of that coupling is that they are doing the same thing - if they are doing different things, you could lose that. :-)
4. Most bass in recorded music is mono, and if you are mixing it, you are probably/hopefully mixing the bass in mono. :-)

Thank you. The only reason I brought up the mono or stereo subs was because another guy told me that I should have the stacked subs in stereo and that didn't sound right to me. Thank you again for your time. -Greg

[John Schalk]

Also, should I have the crossovers engaged on the subs or let the selected crossover points in the PA2 control the subs. I feel like if I engage the subs crossovers, I get a lot more low end. Thanks all in advance.

According to the user guide for the PRX 500 series, the XOVER switch on the PRX518S engages a 120 Hz, 4th order filter on the XLR outputs only. The XOVER switch is not in the signal path for the internal DSP of the subwoofer.  This can also be seen in the block diagram of the signal flow for the PRX518s.  IOW - Unless you have your top speakers connected to the XLR output(s) of the subwoofer, changing the position of the XOVER switch will not change the sound in any way.

[Ivan Beaver]

Hello Greg,

For flipping the polarity - short answer, no.

I disagree-maybe.  It depends on a number of factors.

In many cases you need to flip the polarity on adjacent freq xover ranges.  In many other cases you do not need to flip the polarity.  The "idea" (myth) that all drivers need to be "in polarity" is simply false. It is a nice idea-but there is a lot more involved than simple polarity. They may or may not need to be all the same.

The only way to actually know is to MEASURE it.

Whether or not you flip the polarity on any freq range totally depends on various factors.  Types of crossovers and slopes used, any existing delay to a freq band, actual physical positioning of the cabinets (not just the fronts lined up)

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