From: dpierce@cartchunk.org   
      
   Doug McLaren wrote:   
   > On 2011-08-12, Dick Pierce  wrote:   
   >   
   > |>    -- make it more efficient -- use less power for the same volume   
   > |>       (the power limited is limited, so this is a concern.)   
   > |   
   > | Porting an enclosure WILL NOT make the system any more   
   > | efficient. Not in the least. Ported systems CAN be more efficient,   
   > | not because they have ports, but because they have drivers suited   
   > | for the enclosure that result in electromechanical parameters that   
   > | mke the DRIVERS more efficient to begin with.  ...   
   >   
   > So I have even more to learn about this than I thought -- and I   
   > thought I had a lot to learn before.   
   >   
   > I'll go ahead and not add a port then.   
   >   
   > | You simply cannot just take a pair of speakers, jam them   
   > | in a box, stick a port in it, and expect 1) for it to work   
   > | reasonably well, 2) for it to have "better low frequency   
   > | response and 3) more efficiency. It simply does not work   
   > | that way.   
   >   
   > Sorry I used the wrong terminology.  I was under the mistaken   
   > impression that adding a port could help alleviate the limitations   
   > imposed by the overly small case to some degree -- especially for   
   > lower frequencies -- but at the cost of some sound quality.   
   > (Obviously it's not so simple.)   
      
   It CAN, but you have to know a bit more about   
   the specific physical parameters of the components   
   of the systems to 1) determine if it''s possible,   
   2) figure out how to do it and 3) know when you've   
   done it.   
      
   > My goal is five hours run time, with the volume being as loud as it'll   
   > go and still achieve that goal with the energy available.  At least I   
   > assume that the battery capacity is the limitation -- it may not be.   
   > The batteries should be able to provide 20 watts for 8 hours if the   
   > rated capacity can be trusted, though in my experience it rarely can.   
      
   Let's assume it can. Let's also assume your T-Amp has   
   an efficiency of, oh, 75%. If you assume the 20 watts   
   figure as your draw, then you can reasonably assume only   
   15 of those watts could possibly make it to the speakers.   
      
   And let's further assume the speakers are ideally suited   
   to the amp, in terms of havimg an effective impedance   
   that draws the most effective power from the amplifier.   
      
   Now, there is a notable lack of real and reliable technical   
   information on the drivers, but let's assume my original   
   guesstimate of a reference efficiency of about 89 dB is   
   TRVTH (tm) (and so it shall remain until B3TT3R TRVTH   
   comes along). That means that, at best, your system could   
   produce on the order of about 101 dB or so AT BEST 1 meter   
   on axis of the drivers. And the actual average sound level   
   will be substantially less than  that, unless your only   
   musical interest is ultra-compressed pop stuff.   
      
   So, again, you have to come up with some acceptable   
   definition of "loud" that can be turned into some real   
   design goals. "Loud" doesn't make it.   
      
   And, lastly, making it as loud as possible for you also   
   makes it, likely, TOO loud for those near you who don't   
   share you particular musical and audio proclivity.   
      
   --   
   +--------------------------------+   
   +         Dick Pierce            |   
   + Professional Audio Development |   
   +--------------------------------+   
      
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