ff99cff2   
   From: dpierce@cartchunk.org   
      
   ChrisCoaster wrote:   
   > I'm talking about both woofers having at least a 1" high-profile butyl-   
   > rubber surround that would allow visible movement even when driven   
   > mildly.   
      
   Why? As you might have gathered from some of my other   
   posts, this is, at least, a completely irrelevant   
   technical requirement.   
      
   All other things being equal, for a given excursion, the sound   
   pressure level goes as the square of frequency. Since Fourier   
   tells us that transient must, by their very nature, contain   
   a wide range or frequencies and thus much of the energy is   
   at higher frequencies, the "visible movement" requirement   
   simply ignores physical reality.   
      
   But starting with an excursion requirement is a bass-ackwards   
   way of designing a speaker.. Instead, you start with bandwidth   
   and sound level requirements and see what derives from that   
   in terms of physical parameters.   
      
   >The midrange might also be visibly moved,   
      
   No, I think, given your spec's all the drivers would   
   be visibly upset.   
      
    > My theory is that small rigid cones with high excursion   
    > move as much air as effectively as a huge cone with less   
    > excursion and perhaps not as structurally stiff.   
      
   Well, without some actual exporation of the facts, it might   
   SOUND right, but it's not.   
      
   For a given SPL at a given frequency, the excursion required   
   for a cone goes as the inverse square of the diameter. Thus,   
   working from the relation between diameter, excursion and   
   frequency posted elswhere in this thread, a 12" woofer   
   producing 100 dB SPL at 50 Hz would require an excursion of   
   of about 0.15 cm, in the realm of about 1/16 inches, not   
   much. But a 6" driver doing the same would require FOUR   
   times as much excursion (because its emissive areas is   
   on fourth as great), and 1/4 excursion is beginning to   
   push the limits of linearity in a driver that small. Go to   
   a 4" driver, and you need an excursion of NINE times as much   
   for the same SPL. Building a 4" driver with a half inch   
   of peak linear excursion is simply beyond any reaonable   
   magnet, voice coil or suspension technology. And, because   
   EVERYTHING is smaller with smaller drivers, your heat   
   dissipation gets worse.   
      
   Further, it's VERY difficult to NOT have the Bl product,   
   one of the prime determinant of efficiency, scale with size.   
   Thus, the smaller drivers, despite smaller mass, will not   
   necessarily have the same electroacoustic efficiency and,   
   in most case, end up having less, ameking the power   
   requirements even more severe.   
      
      
   --   
   +--------------------------------+   
   +         Dick Pierce            |   
   + Professional Audio Development |   
   +--------------------------------+   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)