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Classic 2 DIY speaker build whacked frequency curve need help.

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  • Classic 2 DIY speaker build whacked frequency curve need help.

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Name:	classic 2 impedance sweep.png
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ID:	1463876 Click image for larger version

Name:	classic 2 measurement.png
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ID:	1463877 Hello,

    I have built countless DIY speakers and to be honest it takes its toll to open, unsolder, double check everything infinite times to get it sounding how it should be, its a pity I can never get it right the first time but I am sure it will come. So I thought maybe someone can point me in the right direction.

    I was impedance sweeping my speakers when I came across this on the Paul Carmodies Classic 2 so I further investigated with a frequency measurement.

    Does anyone have any ideas why it measures this way? And where can I start looking? I will double check everything but if someone has an idea of what has gone wrong it might help.

    PS. The sweep is from listening position and it does not look normal. I als took one right up close which also had a similar looking result.
    Attached Files

  • #2
    Not familiar with the who, what, where, when, and why of the software/setup used to take the freq measurement, but from the listening seat I've seen worse except for that tweeter taking a dump above 10k.
    And the tweeter dropping off the imp scale above 2k along with the frd measurement seems to indicate something is up.
    http://techtalk.parts-express.com/fo...khanspires-but
    http://techtalk.parts-express.com/fo...pico-neo-build
    http://techtalk.parts-express.com/fo...ensation-build

    Comment


    • #3
      That looks like a shorted tweeter or a short across the tweeter.

      Comment


      • #4
        Change the resolution to 1/6 octave. That's what you can hear, and it's a lot easier to see what's going on without all the fuzziness. The impedance trace is very odd. If accurate I'm surprised there's any output above 8kHz.
        www.billfitzmaurice.com
        www.billfitzmaurice.info/forum

        Comment


        • #5
          Originally posted by Kornbread View Post
          Not familiar with the who, what, where, when, and why of the software/setup used to take the freq measurement, but from the listening seat I've seen worse except for that tweeter taking a dump above 10k.
          And the tweeter dropping off the imp scale above 2k along with the frd measurement seems to indicate something is up.
          Well to be honest I can't remember last time I took a measurement of a so called cheap DIY speaker. I think I'll take measurements of some others and see how they compare. I say that as my higher end DIY are very flat from listening position, so it's interesting you mention you've seen worse.

          But I'll take a look at crossover or try another tweeter. That should tell me what's going on.

          Comment


          • #6
            Originally posted by devnull View Post
            That looks like a shorted tweeter or a short across the tweeter.
            When you say shorted, what exactly am I looking for?

            Comment


            • #7
              Originally posted by billfitzmaurice View Post
              Change the resolution to 1/6 octave. That's what you can hear, and it's a lot easier to see what's going on without all the fuzziness. The impedance trace is very odd. If accurate I'm surprised there's any output above 8kHz.
              Cornbread also mentions the possibility of limited output above around 8k. A while back the tweeters were pushed in so I used a vacuum to suck them out. Can that cause such a thing?

              Either way I'll experiment with another tweeter and double check crossover.

              Comment


              • #8
                I've gotten away with pulling a tweeter dome back into shape many times, guess it depends on how hard it was pushed in.

                " ... my higher end DIY are very flat from listening position, so it's interesting you mention you've seen worse. ..."

                Ok, that scale is 10db increments, so yes, it is a bit wack but yeah, the room can do some crazy stuff. Taken from the listening seat and not gating the response includes all the room contributes to the sound, and unless it is a heavily treated/purposely designed room, the room will contribute a lot to the sound. I've had speakers measure very good outside and when set into their positions, the response looks like a mountain range. It's led me to tear down/redesign a crossover only to find the speakers sounded great, with the original crossover, in another room.

                That dropping imp and frd is very suspicious. Something is up in the crossover/tweeter/wiring/whatever.
                http://techtalk.parts-express.com/fo...khanspires-but
                http://techtalk.parts-express.com/fo...pico-neo-build
                http://techtalk.parts-express.com/fo...ensation-build

                Comment


                • #9
                  Are you measuring just one speaker or are both right and left playing at the same time?
                  Craig

                  I drive way too fast to worry about cholesterol.

                  Comment


                  • #10
                    Tweeters have very fine gauge wire (so, fragile). Depending on your method you could have easily ripped (jerked) the v.c. causing a short. Measure the DC resistance through each of your tweeters' coils. they should be around 3ohms. If zero, you wrecked 'em.

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                    • #11
                      How do they sound? Have you put your ear right up to the tweeter(s) to see if they work?

                      Comment


                      • #12
                        Originally posted by djg View Post
                        How do they sound? Have you put your ear right up to the tweeter(s) to see if they work?
                        I agree - you should be able to hear this long before measurements tell you somethings up. ~40db variations in output should basically sound like its cutting in and out.

                        Impedance curve says the tweeter is straight up dead. It looks like it kind of rolls off with the woofer crossover and then just zip....dead.

                        Originally posted by Trdat View Post
                        When you say shorted, what exactly am I looking for?
                        Positive and negative are essentially connected together. Either through a melted voice coil, wires touching that shouldn't be or some other melted down component connecting positive to negative.

                        Comment


                        • #13
                          Originally posted by Kornbread View Post
                          I've gotten away with pulling a tweeter dome back into shape many times, guess it depends on how hard it was pushed in.

                          " ... my higher end DIY are very flat from listening position, so it's interesting you mention you've seen worse. ..."

                          Ok, that scale is 10db increments, so yes, it is a bit wack but yeah, the room can do some crazy stuff. Taken from the listening seat and not gating the response includes all the room contributes to the sound, and unless it is a heavily treated/purposely designed room, the room will contribute a lot to the sound. I've had speakers measure very good outside and when set into their positions, the response looks like a mountain range. It's led me to tear down/redesign a crossover only to find the speakers sounded great, with the original crossover, in another room.

                          That dropping imp and frd is very suspicious. Something is up in the crossover/tweeter/wiring/whatever.
                          My room is probably over treated and I usually have decent frequency responses so I'll go with the premise that the wiring or something is wrong. Firslty I have a spare tweeter so i'll try that.

                          Comment


                          • #14
                            Originally posted by PWR RYD View Post
                            Are you measuring just one speaker or are both right and left playing at the same time?
                            Both from listening position. You can see the different colors for each speaker.

                            Comment


                            • #15
                              Originally posted by djg View Post
                              How do they sound? Have you put your ear right up to the tweeter(s) to see if they work?
                              I am embarrassed to say that my initial listening test didn't pick up anything, the tweeter was working plus it sounded better than my other two smaller DIY speakers. Of course, this is bigger better tweeter but I din'nt pick up anything weird. But yes the tweeter is working.

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