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   On Wed, 29 Dec 2010 12:45:49 -0500, Randy Yates    
   wrote:   
      
   >On 12/29/2010 12:44 PM, Don Pearce wrote:   
   >> On Wed, 29 Dec 2010 12:05:12 -0500, Randy Yates   
   >> wrote:   
   >>   
   >>> An open-circuit, class D amplifier output has extremely sharp   
   >>> edges due to the switching of the bridge. The expectation is that,   
   >>> somehow, the output is averaged over at least one cycle of the switching   
   >>> period to form a continuous, analog voltage.   
   >>>   
   >>> If this output is connected to a speaker with a mechanical lowpass   
   >>> characteristic, then the speaker's mass will effectively average   
   >>> the "digital" output into a continous position.   
   >>>   
   >>> Thus my question is, when connecting a class D output to a speaker,   
   >>> why do we need filtering at all? That is, why wouldn't the mechanical   
   >>> lowpass filtering of the speaker be sufficient?   
   >>   
   >> Because there are EMI regulations that seriously frown upon high power   
   >> transmitters that broadcast a signal every 40kHz from DC to light.   
   >>   
   >> d   
   >   
   >Apart from EMI, is there a reason?   
      
   Yes. That high frequency square wave would dissipate maximum power   
   into any tweeter connected to it - even without any audio signal   
   present. It has to be suppressed.   
      
   d   
      
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