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DVC wiring effect on T/S parameters

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  • DVC wiring effect on T/S parameters

    I'm in the early planning stages of a three way build; and looking at using 2 SD215A-88 subwoofers for the bottom end (to approximately 300-400 Hz). PE's specs for this driver appear to be with the voice coils wired in parallel. From what I've read, the only parameters that should change if wired in series would be Pe and Re, by a factor of four, correct? When I entered the parameters like this in BassBox, it calculated a 1-W SPL of 86.02 (approximiately the same as with the voice coils in parallel). I then changed the configuration to 2 of these drivers in parallel with a net 8 ohm load for a calculated 1-W SPL of 89.03. Does this make any sense???
    I assumed that the net effect would be the same if each driver was wired in parallel, then connected in series; or vice versa. Is this correct?

  • #2
    Your Pe and Re assumptions are correct.

    A question I would have is how do they spec Le? If the Le spec is for each coil, then the two coils in series will be 2 Le and in parallel will be 1/2 Le. That doesn't take into account any coil to coil interaction.

    Comment


    • #3
      You forgot BL. When wired in parallel, BL will be half of the series arrangement. Sensitivity per watt will remain unchanged.

      Re, Le, and BL all change as you swap wiring modes. However, the changes are complementary, so the effective Qes (and thus Qts) of the driver stays the same.

      In short, don't sweat it - it changes, but the changes cancel each other out.

      Dan Wiggins
      Adire Audio
      "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
      exactly a Fc 3K for both drivers, anybody can do it." -Xmax

      Comment


      • #4
        Originally posted by dcibel View Post
        You forgot BL. When wired in parallel, BL will be half of the series arrangement. Sensitivity per watt will remain unchanged.
        I think this is exactly what BassBox is telling me. PE's published spec for BL (parallel) is 7.7Tm. BassBox calculation (series ) is 15.37.

        The part about sensitivity is what I'm having trouble understanding. If sensitivity is the same for each configuration, then 2 16 ohm drivers in parallel (for an overall 8 ohm load) should have significantly higher overall sensitivity than 2 4 ohm drivers in series (for a comparable 8 ohm load). I know that I'm missing something here.....

        Comment


        • #5
          Huh? Power sensitivity remains the same, voltage sensitivity does not. I don't understand why you think your 8 ohm load will have a higher sensitivity than your...8 ohm load.

          Btw, in your first post, Pe doesn't change whether in series or parallel. The driver can still only dissipate the same amount of power through the same voice coil.

          Anyway, your question has been answered many times before, just do a google search, here's the first thread that comes up for me:
          http://www.diyaudio.com/forums/subwo...arameters.html
          "I just use off the shelf textbook filters designed for a resistor of 8 ohms with
          exactly a Fc 3K for both drivers, anybody can do it." -Xmax

          Comment


          • #6
            Originally posted by dcibel View Post
            Huh? Power sensitivity remains the same, voltage sensitivity does not. I don't understand why you think your 8 ohm load will have a higher sensitivity than your...8 ohm load.

            Btw, in your first post, Pe doesn't change whether in series or parallel. The driver can still only dissipate the same amount of power through the same voice coil.

            Anyway, your question has been answered many times before, just do a google search, here's the first thread that comes up for me:
            http://www.diyaudio.com/forums/subwo...arameters.html
            I think the OP means that, given for a given amp voltage, the coils in parallel will combine to draw 4 times the power than they would in series. decibel is correct, the driver's Pe does not change. But the coil configuration will determine the power to each coil - given the same amp voltage.

            Comment


            • #7
              When I entered the parameters like this in BassBox, it calculated a 1-W SPL of 86.02 (approximiately) the same as with the voice coils in parallel).

              This makes sense. 1 W will move the system the same regardless of the configuration. The trick is; the same wattage going into the total system. Now if the S/W used voltage as the baseline for sensitivity, then the two different resistances would show up in the sensitivity figures. This is the reason driver sensitivity ratings are moving from 1W/m to 2.83V/m. Because voltage depicts sensitivity given an amp's signal amplitude.

              I then changed the configuration to 2 of these drivers in parallel with a net 8 ohm load for a calculated 1-W SPL of 89.03. Does this make any sense?

              I'm guessing that the S/W is splitting the 1 W into each pair of series connected woofers. Thus each series connected pair is at half power, down 3 dB. But then the S/W may add back 6 dB due to the coupling effect between two drivers. Hence the pair of duos is up 3 dB.

              One could also argue that each pair is down 3 dB for a total of -6 dB. Then the pair of drivers' 6 dB bump should negate that: 0 dB difference.

              Or it could be a S/W error. Don't know.
              Last edited by Millstonemike; 02-14-2018, 08:32 PM.

              Comment


              • #8
                Originally posted by Millstonemike View Post
                the coil configuration will determine the power to each coil - given the same amp voltage.
                +1. Technically the coil configuration will determine the voltage to each coil. Wired parallel the same voltage is seen by both. Wired series each coil sees half the total voltage. Taking an amp output of 28.3v as a 'for example' voltage, that's 100 watts into each in the parallel configuration, 25 watts into each in the series configuration.
                The part about sensitivity is what I'm having trouble understanding.
                That depends on what sensitivity you're looking at, SPL per volt or SPL per watt.
                www.billfitzmaurice.com
                www.billfitzmaurice.info/forum

                Comment


                • #9
                  Originally posted by Millstonemike View Post
                  Now if the S/W used voltage as the baseline for sensitivity, then the two different resistances would show up in the sensitivity figures.
                  OK, the light bulb finally came on! I went back into BassBox and the 2.83V sensitivity is also given; and it did go up 6dB. Thank you for your patience with this.
                  I always look at overall sensitivity gain as the efficiency gain (10*log(n)) plus the sensitivity gain (10*log(driver impedance/system impedance)), as given in Jim Griffin's paper on arrays. I did not remember the part about voltage.
                  If anyone is curious why I would go through all this, it is because I read that it was far less desirable to make subwoofer to subwoofer connections in series due to slight differences in speakers that can produce back EMF, distortion etc. Actually, they lost me at EMF, and I just accepted the wiring preference as a rule of thumb. The source was at: https://jlaudio.zendesk.com/hc/en-us...iring-Tutorial
                  Now, I'm going to try to find some mids that would compliment these. Thanks again.

                  Comment


                  • #10
                    FYI: the SD215A-88 is now on sale for $25 instead of the normal $30 during PE's Dayton Audio flash sale.

                    Comment


                    • #11
                      Originally posted by Millstonemike View Post
                      FYI: the SD215A-88 is now on sale for $25 instead of the normal $30 during PE's Dayton Audio flash sale.
                      Thanks -- I did see that. I guess the pressure is on to make a decision and get them ordered. I am also considering the buyout TC8034.
                      I wanted to follow the form factor of this build: http://techtalk.parts-express.com/fo...04-tc9fd-rs225 but with different drivers. This will be my first attempt at a 3-way crossover from the ground up.
                      I looked at the TC9s as mids; but thought I may need something bigger than a 3.5 in driver. The next driver I looked at was the RS100-4, a slight increase to a 4 in driver. Then I noticed that the listed cone area of the TC9 (36.3 sq cm) was bigger that the RS100-4 (35.3 sq cm). I then looked at the Faital 4 in driver, which has published sensitivity numbers that are no where close to my calculations from their specs. This makes planning a little tough.
                      Last edited by kirk78h; 02-16-2018, 01:28 PM.

                      Comment


                      • #12
                        Originally posted by kirk78h View Post
                        Thanks -- I did see that. I guess the pressure is on to make a decision and get them ordered. I am also considering the buyout TC8034.
                        I wanted to follow the form factor of this build: http://techtalk.parts-express.com/fo...4-tc9fd-rs225; but with different drivers. This will be my first attempt at a 3-way crossover from the ground up.
                        I looked at the TC9s as mids; but thought I may need something bigger than a 3.5 in driver. The next driver I looked at was the RS100-4, a slight increase to a 4 in driver. Then I noticed that the listed cone area of the TC9 (36.3 sq cm) was bigger that the RS100-4 (35.3 sq cm). I then looked at the Faital 4 in driver, which has published sensitivity numbers that are no where close to my calculations from their specs. This makes planning a little tough.
                        From some time ago, I think the Faital SPL is in 2pi space.

                        The link doesn;t work.

                        Comment


                        • #13
                          Sorry - it looks like I added a semicolon to the link in post #11. It should be correct now.

                          I also found this thread on the Faital drivers from a few years ago:

                          http://techtalk.parts-express.com/fo...itivity-rating

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