Members djerickson Posted February 8, 2016 Members Share Posted February 8, 2016 Running a pair of JBL 618XLF's under a variety of passive and powered tops for both DJ and live band applications. Normally I'll have a sub on each side of the stage with the top pole mounted above, but the other night I tried placing the subs together (just left of center next to a slightly extended section of the stage) with the tops on stands left and right. I've experimented with the polarity switch on the subs in the past and even went as far as checking all my cables when it seemed i was getting more output from the subs with the polarity switched on one of them. With the subs "coupled" together it became even more evident the switching the polarity on one of the cabinets increased the output of the low end. I'm trying to understand this better. Doesn't this mean the subs are now working against each other? With this new sub arrangement we were experiencing a loud, lower frequency feedback through the monitors. We had to keep them a such a low level to avoid this I was actually hearing more from the mains then the monitors. It seemed like the lead vocal mic was the main offender. With the subs together and placed on the floor (basically along side the lead vocal position) could this have contributed to the problem? Thanks,Doug Link to comment Share on other sites More sharing options...
Members wesg Posted February 8, 2016 Members Share Posted February 8, 2016 I bet your subs are out of phase, but I don't know how to prove it with powered speakers that doesn't involve two microphones and a dual-trace oscilloscope. Why aren't you running high-pass filters on your microphones? Link to comment Share on other sites More sharing options...
Members sibyrnes Posted February 8, 2016 Members Share Posted February 8, 2016 Are you sure you are pushing the polarity button and not the crossover button? Are they the original drivers? I often run XLF's together to benefit from coupling. There is no logical reason why reversing the polarity of one would increase the volume. Link to comment Share on other sites More sharing options...
Members djerickson Posted February 8, 2016 Author Members Share Posted February 8, 2016 On my mixer I've got the 80hz filter engaged on everything except bass guitar and kick drum and have taken most everything below 100hz and above 2 k out of the monitors. It was kind of a fast building roar that just took over everything. We've played this room many times without issue. I'm just trying to figure out if the different sub configuration had anything to do with it or if there's some other issues at play here. (Aren't there always!) Link to comment Share on other sites More sharing options...
Members djerickson Posted February 8, 2016 Author Members Share Posted February 8, 2016 Purchased new......have double checked the push-buttons many times. That's why I was thinking I had a rogue cable somewhere upstream that was wired incorrectly so switching the polarity on one of the subs was actually putting them back into phase. (Is that even a possibility?) All factory cables, no home solder jobs. My eyes tell me one way should be correct but my ears tell me (and others) that switching the phase on one of the cabs increases the overall low end output. I probably used these subs a dozen times or so before ever trying to switch the polarity and while I love the fullness of the sound, I always thought the overall output was a little underwhelming. Is there a chance one of these came from the factory with a wire crossed? Does opening them up to take a look void the warranty? They're still under warranty for another year or so. Link to comment Share on other sites More sharing options...
Members wesg Posted February 8, 2016 Members Share Posted February 8, 2016 What was the approximate feedback frequency? Link to comment Share on other sites More sharing options...
Members Mogwix Posted February 8, 2016 Members Share Posted February 8, 2016 We have a phase tester in our shop but I don't know the make or model ... it came with a CD of test tones (pops and clicks) and a handheld thingy with a microphone and an LED. Sort of like this:http://www.phase-it.com/index.html Link to comment Share on other sites More sharing options...
Members sibyrnes Posted February 8, 2016 Members Share Posted February 8, 2016 How are you sending the signal to the subs? Left and right out of your board or are you daisy chaining, one to the other? Have you substituted other cables? Just because it is a factory cable does not mean it is wired correctly. Link to comment Share on other sites More sharing options...
Members djerickson Posted February 9, 2016 Author Members Share Posted February 9, 2016 Sending left/right from the board to each individual sub. Inputs on the sub are labeled L/R but if I'm using two subs and sending each a left or right signal, does it matter what input is used. Though they're labeled L/R, might they just as well be labeled 1 & 2 or does the right output from the mixer need to be plugged into the right input on the sub? The wiring diagram makes it look as though ot shouldn't matter but I thought I'd ask. Link to comment Share on other sites More sharing options...
Members sibyrnes Posted February 10, 2016 Members Share Posted February 10, 2016 I am wondering if your left and right outputs of your board are not the same polarity. Run one output to one sub and daisy chain to the next sub. See if that makes a difference with your polarity issue. Link to comment Share on other sites More sharing options...
Members agedhorse Posted February 10, 2016 Members Share Posted February 10, 2016 Double-check that pins 2 & 3 are not reversed on one cable. Link to comment Share on other sites More sharing options...
Members Dookietwo Posted February 11, 2016 Members Share Posted February 11, 2016 When you do some testing have the subs about 1 foot apart with the fronts facing each other. Just loud enough to hear things. With music playing you should get a close to 6db increase when you go from 1 sub running to 2. If one is out of phase ( reversed polarity ) the bass will almost drop out completely this way. Check all your xlr cables and check the boards outputs. Link to comment Share on other sites More sharing options...
Members Pro Sound Guy Posted February 11, 2016 Members Share Posted February 11, 2016 If you have an apple device they have an app for polarity testingI have not looked into this for android. I have an Ipad so I ran across this apphttp://www.studiosixdigital.com/audiotools-modules-2/speaker-test-modules/speaker_pop/ Link to comment Share on other sites More sharing options...
Members djerickson Posted February 11, 2016 Author Members Share Posted February 11, 2016 Thanks gentlemen....great advise. Several of you have suggested testing the mixers output. I understand (I think) using a tester to check and see that all cables in use are wired the same, but how does one go about testing the output of the mixer? Do I test the cable going into a particular channel and make sure it matches up with the same pin on the output of the mixer? Link to comment Share on other sites More sharing options...
Members sibyrnes Posted February 11, 2016 Members Share Posted February 11, 2016 Thanks gentlemen....great advise. Several of you have suggested testing the mixers output. I understand (I think) using a tester to check and see that all cables in use are wired the same' date=' but how does one go about testing the output of the mixer? Do I test the cable going into a particular channel and make sure it matches up with the same pin on the output of the mixer?[/quote'] As I said in my earlier post, connect both subs to one output of the mixer and see if that solves your polarity problem. If is does than you know the L+R are out of polarity. There is no logical reason for feeding subs left and right anyway. There is no stereo separation with the lowest frequencies. Do a search on "Aux Fed Subs". That way you are connecting subs to a single source and it might also help your low freq feedback. That being said, I'm still betting on it being a cable. Have you substituted different cables yet? Link to comment Share on other sites More sharing options...
Members djerickson Posted February 11, 2016 Author Members Share Posted February 11, 2016 I'm going to check that out today. When using an amp and passive tops with my powered subs, I'll sometimes use a dbx crossover rather than running an extra xlr back from the sub to the amp. If I summed the output and then daisy chained the subs together would that effectively do the same thing. I'm with you....by chaining them together I can eliminate the problem being with one of the subs themselves and look upstream for another issue. The engineer here at work said to make sure all the equipment in play is wired the same. Is there a manufacturer that's know to wire their gear different than the industry standard. I've got Peavey, AB, dbx, and QSC gear in my main signal path. (He mentioned here at the radio station that our Marti broadcast units invert the 2+ and 3- compared to most all other company's wiring.) Link to comment Share on other sites More sharing options...
Members sibyrnes Posted February 11, 2016 Members Share Posted February 11, 2016 The equipment you mention should all be wired conventionally, but if you connect both subs to the same source it doesn't matter. That way they will be in polarity with each other, and that is the problem you asked about. Link to comment Share on other sites More sharing options...
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