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55-1240 4-unit Z

MzissersonMzisserson
in Hard Data
Broken in for 24 using a function generator at 20Hz well in excess of x-max. 

Seems every driver I purchase from MCM, the Qts is a good deal higher than expected. I would be willing to wager in these units this is from a lower than spec'ed Cms since the Fs of all drivers was on the high side, (except unit 1). Still usable as desired, perhaps less ideal as they originally seemed. Time to start modeling. 


Comments

  • Mitchell_CoteMitchell_Cote
    Kind of reminds me of the MCM 55-2971 $5 eight inch woofes I have.  Maybe there could be a "shoot out of the dumpster 8s."  As always I look forward to your build and thanks for the post. 
  • MzissersonMzisserson
    Mitchell_Cote said:
    Kind of reminds me of the MCM 55-2971 $5 eight inch woofes I have.  Maybe there could be a "shoot out of the dumpster 8s."  As always I look forward to your build and thanks for the post. 
    Thanks Mitchell,

       I have a quad of those 8's feom when they were released. Thwy measire WAY off from spec. Ill never use them at this point. 

    I think the 55-1240 are definately more useful. The top plate says that deapite the conservitave x-max, they will move quite a bit more air. 

    Saw this when burning in. I cycled down to 10Hz and was duly impressed with how well, and quiet they move well past x-max. 

    The Le ia not all that terrible, and the curve is very smooth overall. I think they are going to be great, right through 1.5K if a build needed it...So for very short money fir an 8"woofer, it does not have much sufferage.

    Typicaly, bigger, cheap woofers have one place they flat out suck. Not seeing that here...yet. 
  • jr@macjr@mac
    Mike, I just noticed your Sd is quite a bit different from standard 8" drivers - could you recalculate things with an Sd closer to the 210-215 range?
    I have a signature.
  • MzissersonMzisserson
    jr@mac said:
    Mike, I just noticed your Sd is quite a bit different from standard 8" drivers - could you recalculate things with an Sd closer to the 210-215 range?
     I measured everything, not calculated. I just use the sheet to make it more visible. I will re-check everything, it is possible I made a mistake. 
  • MzissersonMzisserson
    I made a mistake when measuring the effective diameter. I measured the whole surround instead of only including 1/2. It did make a difference in Vas, though not quite as much as I would imagine elsewhere. 

    Here is the result of unit 3 both ways, and the difference in percentage. I am going to get the rest re-measured and will post an updated chart. 

      Unit 3 6.625 Unit 3 7.25 Delta
    Re         = 6.3765 6.3853 100.138%
    Fs         = 45.4466 44.7934 98.563%
    Zmax       = 27.9232 28.2245 101.079%
    Qes        = 1.13 1.1289 99.903%
    Qms        = 3.8184 3.861 101.116%
    Qts        = 0.872 0.8735 100.172%
    Le         = 0.7217 0.7192 99.654%
    Diam       = 168.275 184.15 109.434%
    Sd         = 22239.7074 26633.8103 119.758%
    Vas        = 48.5304 65.7481 135.478%
    BL         = 5.0378 5.5501 110.169%
    Mms        = 15.9604 19.349 121.231%
    Cms        = 690.7033 652.4573 94.463%
    Kms        = 1447.7997 1532.6674 105.862%
    Rms        = 1.177 1.4104 119.830%
    Efficiency = 0.3788 0.4919 129.857%
    Sensitivity= 87.8019 88.9364 101.292%
    Sensitivity= 88.787 89.9154 101.271%
  • MzissersonMzisserson
    Full set #2. I am still sticking with my original thought on these though the Vas is much better. 

    Sd is a funny parameter. It is hard to quantify since in includes the dust cap (which is porous on these), some of the surround, and the cone.  I was way off the first time for sure, would not deny that, however using a measure for eff. diam. including 1/2 the surround has worked very well over the years, most time matching or nearly matching MFG's data for Sd over many brands. So I am going to stick with the 22239 calculation.

    Oh! Thanks, too MCM for a nice foam front gasket instead of layered and knurled cardboard! Much more attractive.  


  • jr@macjr@mac
    I was a little miffled by the higher than advertised Q, but I still plan on using them in something. I am searching for a cheap 8" woofer with an old-timey look but somewhat friendlier T/S for acoustic suspension. If I can snag another pair of Radio Shack 8" poly woofers, they would work swell. 
    I have a signature.
  • R-CarpenterR-Carpenter
    Weak motor?

    Mzisserson
  • MzissersonMzisserson
    jr@mac said:
    I was a little miffled by the higher than advertised Q, but I still plan on using them in something. I am searching for a cheap 8" woofer with an old-timey look but somewhat friendlier T/S for acoustic suspension. If I can snag another pair of Radio Shack 8" poly woofers, they would work swell. 

    I am hanging onto them as well for $11/ea. Yes, frustrating.

    The good news?! The 55-1190's are in and they are breaking in but a very early sign of goodness was out-of-the-box they had a nice, squishy, compliant cone when pushed by hand. Reminded me of old Radio Shack speakers...Or any other speaker good for AS enclosures. No measurements yet, so I am trying not to get my hopes up... 
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