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Quick and Dirty Vas Measurement

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  • #16
    Originally posted by Chris Roemer View Post
    So . . . I measure F-APs, then what?
    Enter "Piston Diameter", then click "Spec M(md)" button and enter mfr. Mms value in Mmd box?
    Then what? Do I have to click "Measure V(as)"? Does DATS have to do another sweep?
    Can't seem to get it to work (using some old data). Please hold my hand on this one?
    (maybe my DATS actually needs to be plugged in to function?)
    Yes. I enter the data as you described and then click "Measure Vas"
    Click here for Jeff Bagby's Loudspeaker Design Software


    • #17
      Originally posted by johnnyrichards View Post
      Is MMS the manufacturer spec we can trust? We see a lot of disparity in calculated MMS sometimes, so I wonder how reliable using this supplied specification over any other supplied specification will be. I understand it is considered a "quick and dirty" method, but...
      The variation we see in calculated Mms is due to inaccuracies in other parameters we are measuring. Most of the manufacturers I have worked with know the weight of their moving parts to within +/- a few grams. This value is likely more accurate than our measurement of effective diameter. And small variations in Mms will not change Vas very much. Many people who measure using delta-mass use too much mass making those results wrong too, so there are a lot of compromises all around.
      Click here for Jeff Bagby's Loudspeaker Design Software


      • #18
        So what is the standard for determining MMS? Sd? Are you allowed to divulge any information provided by manufacturers? I read a convincing article years ago that the "1/2 surround" rule of thumb is optimistic - but have not seen much since.

        I ask because we test drivers using a method intended to bypass manufacturer claims on the premise that they may or may not be bs.
        Don't listen to me - I have not sold any $150,000 speakers.