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Thread: How to determine proper JBL polarity

  1. #1
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    How to determine proper JBL polarity

    Everything I read (non-JBL) says DC current to a speaker pushes the dome or diaphragm outwards. Yet, when I check a know original JBL driver, I get the opposite. I've heard that JBL often wired drivers out of phase, could this be what I'm experiencing?

    Thanks,

    Eric

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    Yes, I've seen all the older JBL is wired so + to the black pushes out (backwards of norm)
    The new stuff is + to the red term so be careful and double check stuff with very low DC voltage (1 or 2 volts) for quick pulses only. I was taught this by a tech at Unistage many years ago. He said you don't want to heat the coils or cause damage by prolonged application of higher DC voltage. So I've always followed this.
    (I'm not a JBL tech! I've just always used them when possible. For something like 40 years now)

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    I'm still wondering what might have provoked JBL to polarize their speakers the other way round . For comptibility reasons I changed polarity in my 2225H subwoofers by reversing the internal hookup cables.

    Best regards!

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    Did they do this with all their older gear? LE15A, LE8T, 375, LE85, 175, 075, 077, etc.? I'm assuming they had to or their own speakers would be out of phase. I wonder when they made the change and if any info was ever sent out regarding mixing and matching new with old, especially with studios and sound reinforcement companies who might need to stick a newer driver in a cabinet with older drivers.

    Eric

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    I retired from pro sound years ago. Back then it was known that their equipment was wired the other way +. Recently I started building another sound system for kicks. I couldn't help noticing that the wiring sticker on the speakers proclaimed that a positive voltage to the red term would produce outward movement of the cone, or something like that.
    So that was on some used JBL's that I just got. They are years old now. So I can only guess at when the change happened. My older woofers (2226 for example) made in the eighties were before the change. So when did they release the newer neodium type woofers? (like maybe the #2258 or newer stuff?) I think that's when the change occurred?

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    That is great!
    So a 2242 18" woofer is opposite the 2241 18" woofers. I have a good idea now with that of why I missed it.
    Thank you I copied it for reference!
    I always check stuff first as I was always afraid of recons not matching. I didn't realize it took place so long ago.

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    Quote Originally Posted by engineerjoe View Post
    I always check stuff first as I was always afraid of recons not matching.
    Always made me wonder on compression drivers. The 2451, for example, is listed as "negative" - but the diaphragms for those are physically compatible with drivers not listed as "negative", and the coated versions of the 2451 diaphragm are popular today as replacements for other 4" drivers. And what about TruExtent? Their 4" diaphragms are listed to work in most all 4" JBL drivers, ones JBL lists as both "positive" and "negative".

    Most guys here will be able to do measurements to see if a driver is suddenly out of phase after a diaphragm swap, but looks to me like a potential source of confusion.

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    Quote Originally Posted by engineerjoe View Post
    That is great!
    So a 2242 18" woofer is opposite the 2241 18" woofers. I have a good idea now with that of why I missed it.
    Thank you I copied it for reference!
    I always check stuff first as I was always afraid of recons not matching. I didn't realize it took place so long ago.
    There are mistakes! From discussion here, seems like about 1 in 50 is backwards. I have a pair of 2241Hs and they are different in that one moves the cone out with + on red while the other goes in as it should. I checked with a compass and the polarity of the magnet is reversed on the former.

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    It's pretty standard now I believe, that pin #2 on a XLR input is positive. I swear when I got started years back, pin #3 was hot? I found some old adapter XLR to stereo 1/4" cords I made many years ago and I had to swap the hot wires to work with modern stuff.I just was making a new system and also found that I had some of my drivers out of phase. So this issue seems current for me. I got a pair of JBL/Selenium 2" drivers to test. Someone removed the rear cover on one and rotated the diaphragm 90 degrees. It wasn't blown just re-installed incorrectly. I got lucky there. So while inside I tested for polarity. I just used an old AAA battery very quickly to observe diaphragm movement. I've never done that before and I'm wondering if I should continue that practice? On my normal JBL cone woofers, I feel that quick pulses of low DC volts (1 volt) won't hurt them. I don't hold on long enough to heat anything up. Just to double check polarity.

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    On compression drivers, if you have red seals on the back cover and don't feel like prying them out to do the battery test, what sort of equipment would you use to check phasing / polarity?

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    Doesn't matter the absolute polarity of the components, only the relative polarity after the crossovers that can shift their phase and it's not always easy or clear and cut. I use an RTA and look for the smoothest response in the seating position and even then there are compromises with polarity.

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    I was reading up about that. Crossovers play a roll in phasing as well as the physical location of the voice coil in relation to other voice coils (in a 2, 3 or more way) system. I use electronic crossovers and multi amps (no passive crossovers). Would it be wise to use a RTA and start with adjusting the delay settings on my electronic crossovers first and only look at polarity change at the speakers if I need more phase shift than the delays offer?

    Of course now you need to distinguish phase shift from time delay and make sure you're not 180 degrees out of phase when using delay. Would the RTA even show that or would that be considered more "reverb" or a degree of "harmonics"??

    Nothing is ever as simple as you might think .......



    Quote Originally Posted by toddalin View Post
    Doesn't matter the absolute polarity of the components, only the relative polarity after the crossovers that can shift their phase and it's not always easy or clear and cut. I use an RTA and look for the smoothest response in the seating position and even then there are compromises with polarity.

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    Quote Originally Posted by toddalin View Post
    Doesn't matter the absolute polarity of the components, only the relative polarity after the crossovers that can shift their phase and it's not always easy or clear and cut. I use an RTA and look for the smoothest response in the seating position and even then there are compromises with polarity.
    I think I can understand that! (I am getting old)
    I have different drivers so the first thing for me is to get an idea of them being in phase with each other and the amps.
    To be honest, my largest system only had 6 horns total back in the day. When I worked on tour they had something like 72 RH horns total. Everything was set up for me and all I had to do was mix!
    My new system is a bash of what I can get my hands on cheap. I bought several different JBL drivers so far. I got a set of 2445, set of 2446, a single 2450 (so far, I want more), a set of Selenium 2" (I forget the numbers) and now even a set of JBL 2430s. I wanted to test the newer stuff to see what I liked.
    I have always preferred JBL 2" horns for their sonic clarity and smoothness on vocals. I also have many 1" drivers that stay on monitor positions. They are just too harsh to my ears.
    So far in testing, the Selenium seem sweeter for stereo use but don't perform as well as the 2446 overall to my ears. For their low price, I considered buying several sets and just not pushing them as hard. They are light weight too. I want to see how they compare to the 2450 still and I need to get my hands on a newer set of the D2 type still. The 2430's have magnets that are decomposing so I need to get newer 2431s (or newer still) and see how they compare. I don't have them mounted to anything yet so I haven't even heard them yet.
    When I finally settle on the horn drivers to my tastes, I still have to compare the waveguide type arrays to my compact 18" bass and 12" mid cabs. I will make a set of the arrays by my design and see how they throw, and how they sound overall. I'm thinking of using 15" JBLs that I already have for lows. They always perform well for me over the years. In a horn type throw cabinet with maybe some 10" mids and a 2450 or 2431 for highs? I'm hoping to fly a couple pairs for long throw park type settings and use my existing compact sets for intimate clubs and short throw apps.
    Sorry for the long winded story here!!!!

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    One more story if I may...?
    I remember a tech coming into a hall and setting up extra stuff for hours. He ran pink noise thru the system, analyzed the system for what seemed like hours, and to speed this story up, the sound lacked when the band played.
    Using that experience, yuck, I always used whatever vocal mic the singer was going to use, and set up the system to my liking by ear. I didn't spend hours phase shifting mids, and aligning stacks, etc. like he did. I think he went by textbooks that didn't work out in real life.
    Reminds me of the sound techs who used the heck out of auto feedback killers and never learned the proper way. Being a musician first and knowing notes and music, helps tune stuff faster and find the resonant frequencies.
    So yes, I am very old school and don't care for the latest greatest stuff for doing what is my job! I will use though, it if it helps me get what my ears want to hear. I have never used any tuning devices in my career. just my ear and common sense.
    Maybe I've been very fortunate to be surrounded by many other talented people too?

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