From: dougmc+usenet@frenzied.us   
      
   I'm making a stereo that is to be mounted on the back of my bike.   
   It's in a box that has internal dimensions of about 12" x 6" x 6" and   
   inside this you'll find a T-amp (it's rated at 100 watts/channel, but   
   I'm not going to power it anywhere near that high) and two 7 Ah lead   
   acid batteries.  Input will come from an iPod that's outside the box.   
      
   It uses two Polk Audio db651 6.5" car speakers, one on either side.   
      
   I know it's not a good speaker design, but sound quality is one of the   
   lesser considerations (weight, size, battery life are also important)   
   -- and really, it's not that bad.   
      
   But I'm wondering if I should port it?   
      
   As I see it, there's a few advantages for porting --   
      
      -- better low frequency response   
      
      -- make it more efficient -- use less power for the same volume   
         (the power limited is limited, so this is a concern.)   
      
      -- if the batteries do vent some hydrogen when charged, it gives it   
         an easy place for it to escape.  It also lets the amp cool a bit   
         easier, though it's so efficient and the power relatively low so   
         I don't think that's a big concern.   
      
   But the stuff on calculating port size is quite confusing.  I imagine   
   I could calculate the frequency of the box (though the batteries and   
   amp inside the box are likely to confuse that calculation) and guess   
   at the Xmax values and go from there.   
      
   I could just guess, put in a port that's about as large as I have room   
   for, though if I understand it correctly, I want to tune the   
   diameter/length so that the wave coming out of the port is in phase   
   with the wave coming out of the front of the speaker -- so it *does*   
   matter.  But wouldn't this calculation only be valid for a specific   
   frequency?   
      
   The calculators I find online talk about calculating things for   
   woofers and subwoofers.  I guess the main speaker *is* a woofer.  But   
   when the calculators as for a frequency ... is it the Helmholtz   
   resonator frequency for the cabinet I should use?   
      
   Maybe I just need to bite the bullet and find a book on speaker design   
   -- since it seems that that's exactly where I'm headed.   
      
   --   
   Doug McLaren, dougmc@frenzied.us   
   --   
   Doug McLaren, dougmc@frenzied.us   
   The dandelion swayed in the gentle breeze like an oscillating electric   
   fan set on medium.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)