PRX618S-XLF Polarity ?

[97delsol]

So I recently pulled the trigger on 2 PRX618S-XLF and 2 PRX625. They sound great and have plenty of power for what I do (Weddings / Corporate events / Small bars & clubs).

I need to understand how the polarity switch works on the subs. It can be set to normal or reverse. They were set on "Reverse" when I first unboxed them....

Having the two subs....with the tops stacked on them.....how should I set the polarity of the subs?

Thanks

[Incognito]

That white organic material with all the black scribble on it that was supplied with the subs when you bought them are blessed with this thing called answers... http://www.jblpro.com/BackOffice/Pro...s/DOC_1672.pdf



So follow that & you're all set, welcome to the forums.

[Bill Fitzmaurice]

Having the two subs....with the tops stacked on them.

First off, don't do that. Subs should be wall or corner loaded, preferably aimed at the wall or corner from about a foot away, and placed together, never split to either side.

...how should I set the polarity of the subs?

Play a sine wave test tone the same frequency as the crossover frequency through the system with only one sub running. Listen to it on the dance floor. Have someone switch the polarity, whichever is louder is the correct setting. Bring the second sub up to the same volume, switch the polarity on that sub, whichever is the louder is the correct setting. You need to do this in every room you play in, as the correct polarity is based on the distance from the subs to the mains and all the room boundaries, so every room will be different.

[GaFFLe]

...Play a sine wave test tone the same frequency as the crossover frequency through the system with only one sub running. Listen to it on the dance floor. Have someone switch the polarity, whichever is louder is the correct setting...

Thanx for posting but I'm not quite following the 1st sentence. So in my case, if I'm trying to test the proper phase of my subs, would I find a sine wav that's 85Hz (which is where I have my LPF set at on my crossover)?

[DJzrule]

If 85Hz is your crossover frequency, then yes, find a sine wave generator and set it to 85Hz.

[Incognito]

If 85Hz is your crossover frequency, then yes, find a sine wave generator and set it to 85Hz.

Fixed...

[light-o-matic]

There are plenty of tone (sin) generator or function generator apps for Android and iOS.. so, get one you like, and keep it on your phone. You'll have it whenever you need it.. just need to carry a 1/8 inch to RCA cable.

Re stacking vs clustering.. clustering is the way to go.. but this is likely a moot point since he's gone and bought double 15's. Unless it is not too late to return them and get something that can go on stands.

Re crossover points, the problem with using an external crossover in this setup is that the PRX sub has a built in low pass (and probably high pass too) that can't be adjusted or defeated. In other words, you are using two sets of filters on the sub, which is probably not what you want. Unfortunately these powered subs don't come with a crossover bypass switch.. so only those that have a crossover frequency knob are friendly to external processor/crossover use. JBL does make a more expensive powered sub which allows for this kind of operation.

[sss18734]

The above advice is good, but realistically not something you're going to do prior to each event.

Since you're pole mounting your mains, just leave the phase on "normal" most of the time. You'll likely see little to no difference between the settings, just make sure you don't run one sub in regular polarity and the other in reverse - in most cases that would decrease your output.

[ampnation]

The above advice is good, but realistically not something you're going to do prior to each event.

Since you're pole mounting your mains, just leave the phase on "normal" most of the time. You'll likely see little to no difference between the settings, just make sure you don't run one sub in regular polarity and the other in reverse - in most cases that would decrease your output.

translation -- it's too much hassle to do things correctly.

I will say that regarding sub placement, Bill is correct that you don't want to have the subs under the tops -- he'll say 100% of the time... I'll say 99% of the time. Sonically, he is correct 100% of the time on that point though. It's just that there are times when the best sound takes a back seat to aesthetic considerations as others perceive them.

Also, a third option he did not mention is clustering the subs forward facing somewhere between your tops. You won't get as much volume this way, but if you have enough SPL, it can work and there are times when you aren't very close to a back wall or corner meaning you would lose more due to the distance than you would gain due to the coupling.

[Bill Fitzmaurice]

The above advice is good, but realistically not something you're going to do prior to each event.

The penalty for not doing so is blown drivers. If he's crossing at 85Hz, for instance, the subs will be 180 degrees out of phase with the tops if they're 6 1/2 feet behind them. That's not hard to imagine. And when that's the case the subs and mains will cancel each other out at and near that frequency. The usual reaction to a cancellation is to turn the subs up, and in the case of a cancellation you can't turn them up enough to fill the hole in the bass before the drivers blow. Testing the polarity takes all of 5 minutes, which is pretty cheap insurance.

Re stacking vs clustering.. clustering is the way to go.. but this is likely a moot point since he's gone and bought double 15's.

Of course he should not have bought 15 loaded tops, let alone 2x15s, but that occurred before he first came here, so it's too late to warn him not to do that. It's not to late to tell him the right way to set up his gear.