Announcement

Collapse
No announcement yet.

Aura Motor Xmax Computed vs. Spec

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Aura Motor Xmax Computed vs. Spec

    PE lists the Aura NS6 Xmax as 3.9mm.

    The spec sheet lists the gap depth as 12.7mm and the VC wind length as 11.3 mm:
    http://www.parts-express.com/pedocs/...ifications.pdf

    Computed Xmax is then very low:
    (12.7 - 11.3)/2 = .7 mm

    I'm wondering if they are rating Xmax at the 70% point on the Bl curve. Then ideally we'd have 30% of the windings out of the gap, or an additional:
    .3 * 11.3 = 3.4 mm which is fairly close to the spec.

    Anyone know how Aura rates Xmax?

    Here's a picture of the Aura Neo Radial Tech (NRT) motor, looks essentially straight forward, no tricks that I can see:
    http://www.crystalmobilesound.com/Soundstage.htm

  • #2
    Re: Aura Motor Xmax Computed vs. Spec

    It is interesting that the NS4 was made with significantly different motor geometries:

    The NS4-255-4C spec sheet:
    http://www.roaster-coffee-shop.com/h...ns4-255-4c.pdf

    has a computed Xmax of:
    (12.7-9.5)/2 = 1.6 mm

    The computed Bl 70% point is then:
    1.6 + (.3 * 9.5) = 4.45 mm

    It is interesting to compare to the -4D version:
    The NS4-255-4D spec sheet:
    http://www.roaster-coffee-shop.com/h...ns4-255-4d.pdf

    has a computed Xmax of:
    (16.7-5.8)/2 = 5.45 mm

    The computed Bl 70% point is then, note that because of the short VC the Bl drops faster:
    5.45 + (.3 * 5.8) = 7.19 mm

    It is interesting to compare the THD at LF and see that the 4C with lower Xmax has THD 40 dB down all the way to 100 Hz whereas the 4D rise in THD starts around 150 Hz. Also the 4C reaches -20dB at 30 Hz whereas the 4D is there at 40 Hz. We'd expect the 4D to be better based on the numbers but as measured it is not.

    Some online spec sheets:
    http://www.roaster-coffee-shop.com/h...0speaker/AURA/

    Comment


    • #3
      Re: Aura Motor Xmax Computed vs. Spec

      It's an underhung coil.
      www.billfitzmaurice.com
      www.billfitzmaurice.info/forum

      Comment


      • #4
        Re: Aura Motor Xmax Computed vs. Spec

        I am aware of that Bill, the calculations are correct for an underhung type.

        Comment


        • #5
          Re: Aura Motor Xmax Computed vs. Spec

          Originally posted by Pete Basel View Post
          I am aware of that Bill, the calculations are correct for an underhung type.
          The correct calculation in this case via the mathematical model is minus 0.7mm. I would assume that the published figure is a Klippel measurement.
          www.billfitzmaurice.com
          www.billfitzmaurice.info/forum

          Comment


          • #6
            Re: Aura Motor Xmax Computed vs. Spec

            You would get minus .7 if you use the wrong formula!

            Comment


            • #7
              Re: Aura Motor Xmax Computed vs. Spec

              Originally posted by Pete Basel View Post
              I'm wondering if they are rating Xmax at the 70% point on the Bl curve. Then ideally we'd have 30% of the windings out of the gap, or an additional:
              .3 * 11.3 = 3.4 mm which is fairly close to the spec.
              Considering the fringe magnetic field outside of the gap, it is probably more than 70% of BL, maybe 80%.

              It is interesting to compare the THD at LF and see that the 4C with lower Xmax has THD 40 dB down all the way to 100 Hz whereas the 4D rise in THD starts around 150 Hz. Also the 4C reaches -20dB at 30 Hz whereas the 4D is there at 40 Hz. We'd expect the 4D to be better based on the numbers but as measured it is not.

              Most probably due to larger voice coil inductance (which under normal conditions indicates more BL modulation by current, and as well Le(i)) of 4D. It has 4 layer of windings, and comparing the impedance curves, it has higher Le.

              Comment


              • #8
                Re: Aura Motor Xmax Computed vs. Spec

                Originally posted by feyz View Post
                Most probably due to larger voice coil inductance (which under normal conditions indicates more BL modulation by current, and as well Le(i)) of 4D. It has 4 layer of windings, and comparing the impedance curves, it has higher Le.
                I seriously doubt that Le differences would impact the distortion at 40 or 100 Hz, however looking at the impedance curves it is clear that the 4C impedance is higher at 100 Hz due to the higher Fs, this would lead to less Bl modulation since it is essentially more efficient.

                Still, I believe that something more complex is going on. Symmetry should eliminate/reduce even order harmonics and the 4C has one of the distortion components level off with decreasing frequency suggesting that it has better symmetry. I'd think that this is a better explanation for the difference. It seems clear that the 4D with a shorter coil is more sensitive to DC offset in the zero position.

                Comment


                • #9
                  Re: Aura Motor Xmax Computed vs. Spec

                  Originally posted by Pete Basel View Post
                  I seriously doubt that Le differences would impact the distortion at 40 or 100 Hz.
                  Higher Le is a result of voice coil being able to generate more of its own magnetic field. Inductance is result of magnetic field generation. So driver having higher inductance will more likely modulate the BL by the higher amount of magnetic field it generates than a lower inductance one. So even though at low frequencies Le has less say because of less reactance compared to Re, the fact that Le is high is an indicator that BL modulation is more likely to happen at any frequency.

                  Comment


                  • #10
                    Re: Aura Motor Xmax Computed vs. Spec

                    I understand your theory but without testing it I'm more inclinded to believe that it is something more having to do with the motor geometry as I previously stated. We can't be sure either way without doing some tests and experiments. One thing to consider is that LF differences are going to be related to excursion whereas midband differences are not.
                    Interesting that the 4D has significantly less 2nd HD midband around 1-2 kHz.
                    Last edited by Pete Basel; 04-07-2012, 10:24 PM.

                    Comment

                    Working...
                    X