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  • Simple PCD Question...

    I'm a little confused as to when a negative or a positive value for "Driver Z Offset".

    I thought if this figure was positive, say .025, it means that the woofer's voice coil is about 1" farther back than the tweeter's when they're mounted on the front baffle.

    I was just looking at Pete's latest project with the Peerless woofers and he has a negative value for z offset.
    How could this be?

    Thank you...

  • #2
    Re: Simple PCD Question...

    Originally posted by foxfire3 View Post
    I'm a little confused as to when a negative or a positive value for "Driver Z Offset".

    I thought if this figure was positive, say .025, it means that the woofer's voice coil is about 1" farther back than the tweeter's when they're mounted on the front baffle.

    I was just looking at Pete's latest project with the Peerless woofers and he has a negative value for z offset.
    How could this be?

    Thank you...
    It depends on the version of PCD you are using. On versions 6.2 and earlier the value is positive for a woofer's acoustic center behind the reference plane (usually the tweeter). In Version 7, however, it is a negative value. I received a lot of requests for this to be made the same convention as most other software, so I ran a poll here on Tech Talk. The winner was to change it to the negative convention. Old csp files will convert to negative when loaded.

    Jeff B.
    Click here for Jeff Bagby's Loudspeaker Design Software

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    • #3
      Re: Simple PCD Question...

      I'm using version 7.00.

      My response looked much better with z being a positive value...too bad it has to be negative as I now have a fairly large dip in my system response.
      Oh well, that's the way it goes I guess.

      Nonetheless, thank you for making it clearer!

      Comment


      • #4
        Re: Simple PCD Question...

        Originally posted by foxfire3 View Post
        I'm using version 7.00.

        My response looked much better with z being a positive value...too bad it has to be negative as I now have a fairly large dip in my system response.
        Oh well, that's the way it goes I guess.

        Nonetheless, thank you for making it clearer!
        Maybe you just need to reverse the polarity on the tweeter and tweak it little from there.
        Click here for Jeff Bagby's Loudspeaker Design Software

        Comment


        • #5
          Re: Simple PCD Question...

          Actually the tweeter's polarity was reversed when I had the wrong value(+.025) in version 7.00.
          This yielded a pretty flat response.

          Using -.025, the smoothest response I'm able to obtain is by using a 4th-order electrical on the tweeter where I was using a 2nd-order before.
          Not sure why...but there's 2 more components to play around with.
          Reversing the tweeter now yields a pretty deep null at the crossover frequency.
          So maybe I'm back on track again.

          Thank you Jeff!

          Comment


          • #6
            Re: Simple PCD Question...

            Originally posted by foxfire3 View Post
            Actually the tweeter's polarity was reversed when I had the wrong value(+.025) in version 7.00.
            This yielded a pretty flat response.

            Using -.025, the smoothest response I'm able to obtain is by using a 4th-order electrical on the tweeter where I was using a 2nd-order before.
            Not sure why...but there's 2 more components to play around with.
            Reversing the tweeter now yields a pretty deep null at the crossover frequency.
            So maybe I'm back on track again.

            Thank you Jeff!
            Are you using minimum phase response files? It seems odd that you would be forced into a 4th order circuit in order to arrive at a decent summation.
            Click here for Jeff Bagby's Loudspeaker Design Software

            Comment


            • #7
              Re: Simple PCD Question...

              Honestly, I don't know how to tell.

              The Peerless 850439 woofer files I got from rjbaudio.com.

              The Seas H1212 files I got from james_e5 here earlier in the year when I was trying to team this tweeter up up with a Seas CA18RNX woofer.

              Thank you...

              Comment


              • #8
                Re: Simple PCD Question...

                as long as we're on this subject, (and maybe you already know this jeff, but) there is some conflicting information on this topic within pcd7. in the popup comment box for "driver z offset" in the "main" worksheet, it correctly states that the woofer's AC being further away than the tweeters should be entered as a negative value. however, in 4.) of the "instructions" tab/worksheet it says "for the z-offset; farther back, like with a woofer's voice coil, is a positive value, since it is added to the listening distance. a negative value here would be subtracted, to indicate that the driver's acoustic center is closer to the listening point."

                i'm guessing the latter is just an overlooked carryover from earlier versions, but you might wanna correct it in the published files none-the-less, since it can lead to some confusion for those of us who read help files (see... wolf's not the only one who looks at them )

                Comment


                • #9
                  Re: Simple PCD Question...

                  Originally posted by absolootbs View Post
                  as long as we're on this subject, (and maybe you already know this jeff, but) there is some conflicting information on this topic within pcd7. in the popup comment box for "driver z offset" in the "main" worksheet, it correctly states that the woofer's AC being further away than the tweeters should be entered as a negative value. however, in 4.) of the "instructions" tab/worksheet it says "for the z-offset; farther back, like with a woofer's voice coil, is a positive value, since it is added to the listening distance. a negative value here would be subtracted, to indicate that the driver's acoustic center is closer to the listening point."

                  i'm guessing the latter is just an overlooked carryover from earlier versions, but you might wanna correct it in the published files none-the-less, since it can lead to some confusion for those of us who read help files (see... wolf's not the only one who looks at them )
                  But did you look far enough? You're right, it is confusing, and I should have changed or made a note on #4 at the top. But, and I guess this comes from writing so much professional documentation for ISO, this is kinda a living document, so you have to follow the revision notes to the current version. Under revisions for Version 7, item 7, this is explained as new for this version. Still I should have added a comment in item 4 at the top.

                  Jeff
                  Click here for Jeff Bagby's Loudspeaker Design Software

                  Comment


                  • #10
                    Re: Simple PCD Question...

                    Originally posted by foxfire3 View Post
                    Honestly, I don't know how to tell.

                    The Peerless 850439 woofer files I got from rjbaudio.com.

                    The Seas H1212 files I got from james_e5 here earlier in the year when I was trying to team this tweeter up up with a Seas CA18RNX woofer.

                    Thank you...
                    To be safe you could use my Response Modeler and extract the minimum phase from the files, save them with new names, import them into PCD, and see if this helps.
                    Click here for Jeff Bagby's Loudspeaker Design Software

                    Comment


                    • #11
                      Re: Simple PCD Question...

                      Originally posted by Jeff B. View Post
                      But did you look far enough? You're right, it is confusing, and I should have changed or made a note on #4 at the top. But, and I guess this comes from writing so much professional documentation for ISO, this is kinda a living document, so you have to follow the revision notes to the current version. Under revisions for Version 7, item 7, this is explained as new for this version. Still I should have added a comment in item 4 at the top.

                      Jeff
                      touche. i did glance at that section, but i'd forgotten about it. while i do intend to thoroughly read the documentation "cover to cover" at some point, due to time contraints my reading thus far has been somewhat cursory and "targeted". i'm certainly not trying to tell you how to do things, but i definitely think it would be of value to those who use the documentation to include a small note or asterisk or something in the "user guide" section, for anything that gets contradicted or amended in any of the revisions sections.

                      ps - i know you've been thanked a million times over, but here's one more. without your software i'd probably just remain content at building others' designs, but thanks to your time and efforts in making such a powerful, easy to use tool, i may well be on my way to designing something of my own.

                      EDIT: i just reread that last paragraph. anyone else think it came out sounding like a marketing quote from an infomercial? oh well, i'm leaving it worded that way anyway... [/threadjack]

                      Comment


                      • #12
                        Re: Simple PCD Question...

                        I've never used your Response Modeler, so I hope I can figure it out using your tuitorial.

                        Is all the software contained in PCD 7.00, or will I need to download other software to get minimum phase files?

                        Thank you...

                        Comment


                        • #13
                          Re: Simple PCD Question...

                          Originally posted by foxfire3 View Post
                          I've never used your Response Modeler, so I hope I can figure it out using your tuitorial.

                          Is all the software contained in PCD 7.00, or will I need to download other software to get minimum phase files?

                          Thank you...
                          The Response Modeler is a separate Excel file. However, the phase extraction only involved clicking one button (on the right, down about half-way) and selecting the frd file that needs the phase extraction. It's as easy as it gets.
                          Click here for Jeff Bagby's Loudspeaker Design Software

                          Comment


                          • #14
                            Re: Simple PCD Question...

                            So, do I need to download Response Modeler for optimum results?

                            Sorry, but I don't see a "phase extraction button".
                            I see a lot of FRD and impedance buttons.
                            I apologize for sounding so dumb...it just seems kinda difficult to learn initially without someone actually walking you through the steps.

                            Comment


                            • #15
                              Re: Simple PCD Question...

                              yes you need to download rm. import the .frd file, hit the 'extract min phase' button. select the frd file, let it do its thing, when requested name a new file, call it ***.frd min phase. done. inport this to pcd
                              " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

                              Quote Originally Posted by hongrn. Oct 2014
                              Do you realize that being an American is like winning the biggest jackpot ever??

                              http://www.midwestaudioclub.com/spot...owell-simpson/
                              http://s413.photobucket.com/albums/pp216/arlis/

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