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Inches to Ohms

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  • #16
    https://sites.google.com/site/undefi...diy-sunflowers


    Paul Carmody has some insight into the open back midrange design.

    Under "Crossover Design"

    He mentions and describes a dipole "Peak" that boosts the sound at a certain dimension of the baffle versus frequency.

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    • #17
      Originally posted by craigk View Post

      No
      Too bad . Assuming baffle width equates to diameter ,
      most of the world uses ( in inches ) 4560 / baffle width
      to calculate the point at which an open baffle drops off at the
      low end . They define this as Fc and / or F3 . It is nice to be
      in the company of such an enlightened group .

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      • #18
        Originally posted by hitsware2 View Post

        Too bad . Assuming baffle width equates to diameter ,
        most of the world uses ( in inches ) 4560 / baffle width
        to calculate the point at which an open baffle drops off at the
        low end . They define this as Fc and / or F3 . It is nice to be
        in the company of such an enlightened group .
        Just like I said from the start, your math and assumptions are wrong. Not enlightened at all, just able to do a little math. Your problem is assuming things. We all know assumptions lead to.
        craigk

        " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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        • #19
          My " problem " is using a simple model .
          I believe it comes closer than yours to predicting
          what is normally perceived in room .
          Comb filtering is real , but in normal situations ,
          mostly masked .

          ( FWIW ) ..... Here is how I model an open baffle system :

          Place driver ( Fs , Qts , Vas ) in sealed box .
          Set box size to 100 * Vas .
          Limit frequency response with a high pass filter ( based on baffle width )
          Perhaps my reality is skewed , but this pretty much fits what I hear .

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          • #20
            Do you have a camera or smartphone? I'd love to see your finished projects. I just heard SilverD's little Nola Brio clones and was very impressed with the sound. I'm building a pair with a cab kit from him.

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            • #21
              Originally posted by djg View Post
              Do you have a camera or smartphone? I'd love to see your finished projects. I just heard SilverD's little Nola Brio clones and was very impressed with the sound. I'm building a pair with a cab kit from him.
              I thought you would never ask Click image for larger version

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              • #22
                Thanks.

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                • #23
                  Originally posted by hitsware2 View Post
                  O.K.

                  May we say ?............. ( f 3 not f c ) :

                  f3 = 4560 / WB ............ ( where WB = width of the baffle in inches )

                  First of all you can not apply these rules to anything but a circular baffle. Second, If you assume 13500 ips for the sound speed, the Fc = 13500/D. This is the dipole peak and also the corner frequency of a 1st order filter which will match the dipole roll off. fx = 4500/d = f10 or the frequency where the 1st order filter is 10dB below the flat band response. It is also where the dipole response is equal to that of the monopole sources, 0 dB. Thus, once again, as I posted above, a 1st order HP filter with 10dB gain will match the dipole response.

                  See this web page of mine where I discuss how to find the equivalent circular baffle for a given rectangular baffle size, which will yield the same low frequency response below approximately fx. http://musicanddesign.speakerdesign....t_Baffles.html
                  John k.... Music and Design NaO dsp Dipole Loudspeakers.

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                  • #24
                    Your web pages are works of art , as well as ( I assume ) science .
                    The math is way beyond me .

                    As far as nit picking baffle size I use the " shortest diameter "
                    I.E.......
                    For a 24 " x 48 " rectangular baffle ...
                    If sitting on the floor on the 24 " side then diameter ~ 24 "
                    If sitting on the floor on the 48 " side then diameter ~ 48 "
                    For my baffle less drivers above , diameter ~ driver size

                    What is the significance of the " 10 db " gain for your HP description ?
                    Isn't the FR curve the same as sans gain , only offset by the 10 db ?

                    Comment


                    • #25
                      Originally posted by johnk... View Post


                      First of all you can not apply these rules to anything but a circular baffle. Second, If you assume 13500 ips for the sound speed, the Fc = 13500/D. This is the dipole peak and also the corner frequency of a 1st order filter which will match the dipole roll off. fx = 4500/d = f10 or the frequency where the 1st order filter is 10dB below the flat band response. It is also where the dipole response is equal to that of the monopole sources, 0 dB. Thus, once again, as I posted above, a 1st order HP filter with 10dB gain will match the dipole response.

                      See this web page of mine where I discuss how to find the equivalent circular baffle for a given rectangular baffle size, which will yield the same low frequency response below approximately fx. http://musicanddesign.speakerdesign....t_Baffles.html
                      Hitsware ust to point out, that i was correct, and you were not, again. Maybe i am enlightened after all. But besieds, that this is an interesting priject. I am curious to see how the project comes out.
                      craigk

                      " Voicing is often the term used for band aids to cover for initial design/planning errors " - Pallas

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                      • #26
                        > I am curious to see how the project comes out.

                        Ohms to inches ?
                        It obviously works . The question ( brought up with such gusto )
                        is the not the translation , but the number of ohms ( inches ) associated
                        with a given roll off . ( determined by the value of capacitor )
                        Also the definition of open baffle roll off itself .
                        The ' comb filtering ' effect could be demonstrated by Ohms to inches
                        with the right circuit attached to the resistor .

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                        • #27
                          Ohms to Inches to Seconds Click image for larger version

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                          • #28


                            Click image for larger version

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                            • #29
                              Originally posted by hitsware2 View Post

                              What is the significance of the " 10 db " gain for your HP description ?
                              Isn't the FR curve the same as sans gain , only offset by the 10 db ?
                              It set the 0dB level to the dipole = monopole frequency. Thus, if you are building a dipole using a driver with XX dB sensitivity the equalized dipole response will have the same sensitivity at that frequency. Something you need to know when designing a circuit to equalized the response.
                              John k.... Music and Design NaO dsp Dipole Loudspeakers.

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                              • #30


                                Click image for larger version

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ID:	1429709 > Something you need to know when designing a circuit to equalized the response.

                                That wouldn't be important for a single full range driver system , right ?
                                Trying to put together equalization networks to make my bare drivers listenable is
                                what led to " Ohms to inches "

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