Magnum-15 (Titan/15” MBM) discrepancy

Discussion in 'Speaker Components' started by Brinkman, Jul 27, 2020.

  1. Hi Matt,

    Over at AVSForum you provided the following T/S parameters for the Magnum-15 woofer:
    Sd = 881 cm^2
    f(s)= 35.64 Hz
    R(e)= 3.93 Ohms
    Q(ms)= 6.474
    Q(es)= 0.393
    Q(ts)= 0.370
    V(as)= 222.4 liters (7.854 cubic feet) L(e)= 1.33 mH
    n(0)= 2.492 %
    SPL= 96.12 1W/1m
    USPL= 99.21dB
    M(ms)= 98.7 grams
    C(ms)= 0.202 mm/N
    BL= 14.87
    Xmax= 12mm
    Pe= 600w

    When I measured the pair I recently purchased, DATS displayed both as having a V(as) within a few liters of 100 and a higher Q(es) of around .47. My M(ms) is also consistently 50% greater. I had to add about 150g of added mass to get the V(as) measurement, do you think this is the reason for the discrepancy? Modeling your T/S vs mine in WINISD yields enclosures differing by 2cu ft. Note sure I feel confident with my measurements.

    thank you
  2. What are the full specs from your DATS measurement?

    Sometimes the individual values can look like they fluctuate wildly but often the modeled response when comparing the drivers in the same enclosure will be within 1dB.
  3. R(e) = 4 ohm
    F(s) = 40.7 Hz
    Q(ts) = .438
    Q(es) = .47
    Q(ms) = 6.63
    L(e) = 1.23 mH
    M(ms) = 158.75 g
    V(as) = 99.3 l
    SPL (2.83v) = 96.45 dB

    this is the two drivers averaged; both units were consistent with each other. I used DATS latest version.
  4. I should mention that when I do the added mass to get V(as) I orient the driver in an upright position, like it would be oriented on a baffle.

    I used these same methods to measure my Vortex-15 woofers and they were both dead-on the T/S that was provided.
  5. And as I mentioned in the first post, modeling your provided T/S for these drivers and my measured T/S in WINISD yields ported enclosures differing by around 2 cu ft. That seems significant to me.

    I wonder if these differences are due to this specific driver having it’s V(as) measured using two different methods, added mass vs sealed box?

    The underside of both cones is stamped 18 291. Maybe we should compare and see if they’re from different batches.

    I‘m going to remeasure tomorrow but if the T/S doesn’t change, I’m going to assume one of us is in error (probably me), DATS is inconsistent (not likely), or the specs may have drifted in manufacturing (possible).
  6. My driver is much older, 15-190 (I'm guessing it's year and day of manufacture?).

    I pulled my driver out and tested it a bunch of different ways with different mass added to the cone (I normally use the mass added VAS method) but couldn't really replicate your results.

    Have you broken in your drivers at all?

    Here is a link to the DATS file for the measurements I took today

    1 and 3 were taken with the driver sitting flat while 2,4 and 5 were with the driver upright. I normally measure with the driver sitting flat on a hard heavy surface usually on the top of a speaker box with 2x3's under the magnet as it's easiest to get the most consistent results and prevents the driver from moving or shaking at all which skew the results especially with heavier coned woofers/subs.

    The biggest or most noticeable difference seen between the different measurement directions is in the Qms (height of peak at resonance) but that will result in little difference in the models.
    Brinkman likes this.

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