From: trevor@home.net   
      
   On 3/12/2014 12:21 AM, Mark Zacharias wrote:   
   > "Trevor"  wrote in message   
   > news:m5jjac$s85$1@speranza.aioe.org...   
   >> On 2/12/2014 12:19 AM, thekmanrocks@gmail.com wrote:   
   >>> geoff:  My 1995 JVC receiver specifies 8-16ohms.  Guess that's an   
   >>> oldie then!   
   >>>   
   >>   
   >> Many cheap receivers with limited current capability specify 8 ohms or   
   >> more, regardless of age. Conversely many good amps can handle loads as   
   >> low as 2 ohms without a problem.   
   >>   
   >   
   >   
   > Speaker impedances have not really changed - they are rating them a bit   
   > more accurately these days.   
   >   
   > Mark Z.   
      
      
   Partly true to the second part, mostly no to the first part. Some   
   manufacturers use the impedance minimum fairly closely these days.   
   Others are just an estimate of what they think the amp rating should be.   
   But speaker impedances HAVE generally dropped over the last 50 years or   
   so. First with the change from valve amps they generally went from   
   ~16ohm to 8ohm. Then with the improvement in current handling of   
   transistor amps (and the increase in multiple small bass drivers vs one   
   larger driver), many have dropped from ~8ohm to ~6 or 4 ohm.   
   In any case ALL speakers vary wildly in *impedance* across the frequency   
   range, especially ported speakers, but the voice coil *resistance* of   
   many drivers has decreased. That affects the system impedance, and is   
   easy to measure. And some manufacturers still produce their drivers with   
   voice coil resistance options, or even custom make them if you buy enough.   
      
   Trevor.   
      
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