Home dbx User Forum dbx Archive Threads DriverRack PA & DriveRack PA+ PA General Discussion

Phase problem

bobdbobd Posts: 7
edited August 2007 in PA General Discussion
I have configured the DRPA for a 2x4 bi-amplified system and find that the two outputs (high, low) are out of phase with each other. Cross-checking my settings proves that it is the DRPA that is doing the phase inversion on one channel (either high or low). I can't seem find out where this is set.

Can someone tell me how to change the phase of one of the channels.

Thanks,

Bob.

Comments

  • the Drpa doesnt have 'phase' adjustment capability built in.

    if youre getting phase problems try swapping polarity with your subs at the speakon plug......
  • DraDra Posts: 3,777
    Are you having a phase problem between L & R or between High & Low?

    If you have a cable checker or volt meter check that all pins match up 1 - 1, 2 - 2, 3 - 3 on your XLR cable and that all speaker cable are wired the same.

    DRA
  • kpippenkpippen Posts: 551
    The speakers are easy to check... Use 9-volt battery and with your speaker wire (amplifier side and un-hooked) touch + to + and - to -... If your driver pushes outward phase is correct...

    Kevin
  • bobdbobd Posts: 7
    Problem solved but I've no idea what caused it in the first place. The configuration I had was based on one of the wizards (the wrong one) and I can't remember which one I used. It apparently inverts the phase of either the highs or lows. I just did a new configuration based on a different wizard and all is well.

    Thanks,

    Bob.
  • bobdbobd Posts: 7
    Tech note: My apologies for using the word phase, the correct term is, of course, polarity.

    Bob.
  • kpippenkpippen Posts: 551
    Hi Bob,

    Thanks for posting back... Glad to hear that all is well...:)

    Kevin
  • DraDra Posts: 3,777
    Gadget , Kevin...

    Obviously it was not a routing cable or speaker mis-wiring issue. What could have been the problem here? Does the DRPA have a secret config for change polarity? :idea: :idea: :idea: :?: (read, \"Ideas?\")

    DRA
  • GadgetGadget Posts: 4,915
    Good morning all...

    Here is the most likely scenario...JBL!!! :twisted: In a word.. they wind a good number of their speakers and drivers reverse..yes thats plus to plus yields a toward the magnet motion. Why they did this remains a mystery to this intrepid writer...So I must assume you chose a preset with a JBL speaker that has one speaker wound one way and the other wound the other. I believe I have a list of just what drivers are what winding...but I couldn't find if off hand... 8)

    Now, here I guess I should indicate that some of the crossover designs do create phase shifts that predicate some manufacturers to reverse the polarity of the horn driver. We used to have a crossover guru here but he has moved over to the PSW, his name is Lee Patzius and you can look up his threads on the former forum...That should not be an issue here but you can definitely affect the clarity/intellegibility of the signal via the use of the phase shift when you are tuning a speaker via an active crossover. Thats what makes the 260 such an invaluable tool when you want to perfect the tunings of your speakers. There are a number of methods posted on the net if you look them up, but the best way is with an FFT based measurement system that takes phase into alignment consideration.

    The more you learn.. the less you find you know, but ignorance is NOT bliss!

    Good day folks!

    Be well
    Gadget
  • kpippenkpippen Posts: 551
    Gadget wrote:
    they wind a good number of their speakers and drivers reverse..
    Gary,...I vaguely recall you mentioning that once before...over the phone I think?... It would be a good thing if could remember this stuff for quick access... Too much exposure in the seventies I guess...
    pot.gif

    Hey,...I've been hoping you would share some personal history with us?...

    Kevin
  • MikeyMikey Posts: 82
    If you don't mind, I'd like to share a little history with you about JBL...

    So, I'm working in a local church that has some severe problems with sound. The room and the speakers were a match made in hell. Anyway, we start with the speakers because something sounded a little strange right from the get go.

    First, I disconnected one of the JBL SRX722s from each side. Yes, some dufus actually recommended that they use these in pairs on each side of the stage. But, back to the issue at hand...

    I put a little pink noise through the system and did a little listening. Not happy. Set up my Smaart rig and did a little testing. Less happy. One of the HF drivers in one of the boxes had polarity reversed. Took the boxes down to fix the problem and even less happy.

    Of the four cabinets, one of them did not have the correct HF driver in it. It wasn't even the one with the polarity reversed. So, now two of the four are not right.

    I won't even get into the details of JBL's response. After a month of screwing around with the morons, I finally told the client they had to deal with this problem. Those guys have no idea what they are doing. Couldn't read the Smaart ref file so I did a a screen shot and then had to explain it to them. They wouldn't let me talk to an engineer.

    The worst part is that the boxes didn't even meet spec. The published frequency response curves are off by about 9KHz on the high end. I indicated this to them almost a year ago and their response was that they might have made a mistake in the data they published. Duh. Same wrong data is still being shown by the company.

    Anyway, I spec hundreds of thousands of dollars worth of equipment a year. With this kind of customer service and made up technical data, guess what brand is now on my \"do not spec\" list?

    I have a transfer function of that data if anyone would care to see it. I tried to push it to the board a month or so ago when someone was looking at those speakers and couldn't get it up. Maybe Gadget can push it if there is interest.

    End rant,
    Mikey
  • kpippenkpippen Posts: 551
    Guys,

    Here's a screen shot of the data that Mikey's referring to:

    brandy.gif

    Check-out the tab on the top left-hand corner...sleepy.gif

    Kevin
  • GadgetGadget Posts: 4,915
    Yup... thats what Mikey was telling me...can't even make 12K... and the spec sheet says???????????????????????????????????????? Oui Vei... Anybody wanna spend big bucks on a set of \"hi end\" JBL's now? Thats why we need some sort of standardization in loudspeaker measurements...ther are NONE! a speaker MFG can pretty much write anything they want about a product and get away with it... As I have said before and I will say again.. I am NOT a big JBL fan!... you can search that out to verify if you want.. I also target BOSE any chance I get...

    Gadget
  • kpippenkpippen Posts: 551
    Sooo..I guess JBOSEL is out of the question?...:lol:
  • MikeyMikey Posts: 82
    I'll try to get the phase data from that particular cabinet that I mentioned. I'm not sure if I saved it in the .ref file or not. I don't think so, but I'll check.

    BTW, that huge dip in the orange trace should speak to anyone who thinks that any ol' speaker can \"array\" if put side by side. This is what happens to the frequency response. Now, it changed at different locations in the room, but it still has that general nasty dip. The blue trace was just one speaker active.

    Thanks to Kevin for putting this up for me!

    Hope this was helpful to someone.

    Mikey
  • DraDra Posts: 3,777
    They missed their low-end by a full octive +. I guess it's easier to market a speaker if adding a sub makes it fly. Kind of hard to sell if the slogan is, \"Just add any long-throw powered tweeter box on top, with our patented universal mounting bracket assembly #POS1SUKA (sold separately) and your ready to rock the house.\" 8)

    DRA
Sign In or Register to comment.