XPost: alt.audio.pro.live-sound, rec.audio.pro   
   From: digilyd@hotmail.com   
      
   Phil Allison wrote:   
      
   >> I'd just replace the bulb with a soldered in polyswitch,   
      
   > ** Bad idea.   
      
   > Incandescent bulbs provide a better solution for live sound apps.   
      
   > They allow all transients and normal levels through and rapidly   
   > compresses ( without distortion ) exceptional levels  -  like   
   > feedback howls -  to a tolerable level for the HF drivers.   
      
   It is less bad, agreed.   
      
   > OTOH,  a Polyswitch cuts the sound almost right off ( without any   
   > warning) and takes quite a while to re-set after tripping.   
      
   The result of playing something with unexpected 40 Hz content on Celestion   
   RS1220 is a gunshot-like sound that scares horses.   
      
   Relative comparison of voltage sensitivity for all units:   
      
   8 ohm 9135815     4 ohm 9090530     4 ohm 9090546   
      
   treble -16.78     treble -21.62     treble -24.73   
      
   mid -34.77        mid -43.36        mid -48.2   
      
   bass -41.61       bass -42.87       bass -43.22   
      
   Input signal to box: white noise, bass units has mic 1 cm from center dome,   
   mid horns has mic far enough away to be clear of box edge reflections and   
   treble units has mic once cm away. dB values are "average loudness" with a   
   300 ms window as determined by CE2k. 2 conclusions are obvious: bass unit   
   voltage sensitivity is as predicted by Dick Pierce and both 4 Ohm boxes need   
   service. So this seems to have been the end of a very long winnning streak   
   in buying second hand equipment, win some, loose some, now gain knowledge to   
   offset loss.   
      
   Finally got feedback from Yorkville. Both 4 Ohm boxes suffer from   
   deteriorated x-over or midrange driver or mis-mounted midrange drivers or   
   dirty midrange drivers or "all of the above". Midrange driver gasket is   
   visually misplaced - protruding 3 mm into the horn - in one of them.   
      
   Next to do:   
      
   1) measure output frequency response directly from x-over   
      while loaded with units   
      
   2) remove midrange drivers and measure frequency response sans horns on   
      
   3) expected result: get a new version eminence screw-on and just remove the   
   piezos.   
      
   Voltage sensitivity of 8 and 4 ohm bass loudspeaker versions is near   
   identical, which is what made me not simply put the 4 Ohm PL315's in a   
   dumpster and move on. Midrange output from 8 Ohm box is basically linear, 4   
   ohm boxes are differently unlinear.   
      
   > ....  Phil   
      
      Kind regards   
      
      Peter Larsen   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)