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Suitable transformer for MidWooferMidrange Speaker Break-in? . . .

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  • Suitable transformer for MidWooferMidrange Speaker Break-in? . . .

    Seeking advice/PE available AC wall-wart/transformer suitable for leaving connected to a pair of 4 Ohm speakers for a week at a time (60Hz) and any necessary series (voltage-dropping) resistor values/Wattage.

    It's been a long time since I did this and using the PC isn't my best option.

    Thanks for your well considered thoughts.

    Merry Christmas.




  • #2

    Might I suggest just doing it overnight from the PC as I am assuming it is inconvenient to do so during the day. Even a 5V is probably too much as it does not take much around Fs. Not very loud as in free air, you get the front to back cancelation.

    Do a simulation and see how much power it takes to reach 1/2 X-max maybe @ 60 Hz. Then P=IE, E=IR. Do the math.

    Comment


    • #3
      I'm not really concerned about the 1/2 Xmax value of power nor want to spend time modeling it - just want to put a signal on the coil that will exercise the driver for while uninterrupted.

      2.83 volts is a standard for testing speaker sensitivity, I'll use that as a starting point for the calculation.

      So my 4 ohm-nominal speaker has a DC resistance of 3.6 ohms and an RMS power handling rating of 100 Watts with an Xmax of 12 mm - one-way.

      I = E/R; 2.83 / 3.6 = 0.7861 Amps.

      P = IE; 0.7861 * 2.83 = 2.2247 Watts - Hardly pushing the cone at all - I'll use this as a 1st pass break-in voltage.


      Now lets use a filament transformer with a 2ndary output voltage of 6.3 Vac:

      I = E/R; 6.3 / 3.6 = 1.75 Amps.

      P = IE; 1.75 * 6.3 = 11.025 Watts - looks doable in open-air considering the high Xmax rating of the speaker and should be sufficient for the final pass break-in voltage.


      Now, I'm off to the shop to dig around for old stored transformers . . . and voltage dropping resistors . . .


      Thanks.

      Comment


      • #4
        A PC, download this SineGen sine wave generator from my Google drive and an amp. You want to start out at a very low volume and adjust the frequency for maximum cone excursion. That's the woofer's Fs and that's the way to break in a speaker (in free air, not boxed). 60 hz may be outside the range where the woofer's suspension will really be exercised.

        SineGen does not "Install" in windows. Just download it and double click on the icon to run it (ignore the warning). No adware, malware, etc. Several members here have use it no problem. You can actually type in the desired frequency in the upper left hand corner (among other ways to adjust it). The power button turns the signal on and off. And the slider bars are another way to control volume in addition to the PCs volume control and any controls down stream.


        Click image for larger version

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        Comment


        • #5
          Originally posted by Steve Lee View Post
          I'm not really concerned about the 1/2 Xmax value of power nor want to spend time modeling it - just want to put a signal on the coil that will exercise the driver for while uninterrupted. 2.83 volts is a standard for testing speaker sensitivity, I'll use that as a starting point for the calculation. So my 4 ohm-nominal speaker has a DC resistance of 3.6 ohms and an RMS power handling rating of 100 Watts with an Xmax of 12 mm - one-way. I = E/R; 2.83 / 3.6 = 0.7861 Amps. P = IE; 0.7861 * 2.83 = 2.2247 Watts - Hardly pushing the cone at all - I'll use this as a 1st pass break-in voltage. Now lets use a filament transformer with a 2ndary output voltage of 6.3 Vac: I = E/R; 6.3 / 3.6 = 1.75 Amps. P = IE; 1.75 * 6.3 = 11.025 Watts - looks doable in open-air considering the high Xmax rating of the speaker and should be sufficient for the final pass break-in voltage. Now, I'm off to the shop to dig around for old stored transformers . . . and voltage dropping resistors . . . Thanks.
          3.6 ohms at DC is definitely not equal to R at 60Hz. Depends on the speaker, particularly how close that is to Fs. If you can't measure, look for a spec sheet with a Z chart and find the impedance at 60.

          Then again, the power doesn't matter exactly anyway as long as it's less than the thermal limit. A 6.3VAC tap should be safe enough. Line voltage is pretty dirty though, so it'll make more noise than a clean sine wave.

          A sine generator into an amp so you can target resonance and adjust how hard you're driving is still the best action.
          Electronics engineer, woofer enthusiast, and musician.
          Wogg Music
          Published projects: PPA100 Bass Guitar Amp, ISO El-Cheapo Sub, Indy 8 2.1 powered sub, MicroSat, SuperNova Minimus

          Comment


          • #6
            That is a really cool program. You kind of have to use it a bit to really appreciate how useful it is.

            It's also a good tool for bass vocal warm-ups.

            TomZ
            Zarbo Audio Projects Youtube Channel: https://www.youtube.com/channel/UCEZ...aFQSTl6NdOwgxQ * 320-641 Amp Review Youtube: https://youtu.be/ugjfcI5p6m0 *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
            *Part 2 *Gluing multiple curved laminations of HDF

            Comment


            • #7
              Originally posted by Steve Lee View Post
              I'm not really concerned about the 1/2 Xmax value of power nor want to spend time modeling it - just want to put a signal on the coil that will exercise the driver for while uninterrupted.

              2.83 volts is a standard for testing speaker sensitivity, I'll use that as a starting point for the calculation.

              So my 4 ohm-nominal speaker has a DC resistance of 3.6 ohms and an RMS power handling rating of 100 Watts with an Xmax of 12 mm - one-way.

              I = E/R; 2.83 / 3.6 = 0.7861 Amps.

              P = IE; 0.7861 * 2.83 = 2.2247 Watts - Hardly pushing the cone at all - I'll use this as a 1st pass break-in voltage.


              Now lets use a filament transformer with a 2ndary output voltage of 6.3 Vac:

              I = E/R; 6.3 / 3.6 = 1.75 Amps.

              P = IE; 1.75 * 6.3 = 11.025 Watts - looks doable in open-air considering the high Xmax rating of the speaker and should be sufficient for the final pass break-in voltage.


              Now, I'm off to the shop to dig around for old stored transformers . . . and voltage dropping resistors . . .


              Thanks.
              All that is fine, but at Fs it takes a lot less power for higher excursion. You also might look into the difference between DC resistance and impedance just for furthering your understanding.

              Comment


              • #8
                Originally posted by tomzarbo View Post
                That is a really cool program. You kind of have to use it a bit to really appreciate how useful it is.

                It's also a good tool for bass vocal warm-ups.

                TomZ
                Yes, that is a neat tool. I've been using it for finding out what's going on in several pairs of headphones. It's really revealing. When I can hear those big peaks and troughs that show up on the response graphs, I wonder why they don't sound awful. So far, the 40 year old pair of Pioneer SE-305s I picked up for $4 at a thrift store are holding their own. They are big, heavy, and very comfortable. Kind of like the cars from the 70s I've had.

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