XPost: sci.electronics.basics   
   From: spam@spam.com   
      
   On Mon, 21 Nov 2011 11:44:56 +1100, "Trevor"  wrote:   
      
   >   
   >"Don Pearce"  wrote in message   
   >news:4ec7817b.5640231@news.eternal-september.org...   
   >>>> Echo is a single reflection of a sound - the kind you hear when you   
   >>>> shout "Hello" near a cliff.   
   >>>   
   >>>Multiple reflections are also common in such instances.   
   >>>   
   >>   
   >> No they are not. One cliff, one echo. No choice.   
   >   
   >In the real world cliffs are not usually one straight smooth edge of course.   
   >   
      
   My mistake. I thought I was talking about a hypothetical cliff. I now   
   find I was in fact talking about a cliff that you know personally, and   
   has multiple faces. Would you care to introduce me to it so I can   
   perform a mathematical analysis? That will obviously make things much   
   simpler for the OP.   
      
   >   
   >>>> Feedback is a situation you only get when you have an amplifier and a   
   >>>> speaker. The sound arriving from the speaker is a little louder than   
   >>>> the one that originally hit the microphone, so that comes out of the   
   >>>> speaker a little louder still. This loop will build until the system   
   >>>> howls.   
   >>>   
   >>>That would be *acoustic feedback* only, There are MANY other types of   
   >>>course.   
   >>>   
   >> In the context of the question it would simply be confusing to discuss   
   >> - or even mention - other kinds.   
   >   
   >If you prefer to simplify things so much you at least need to point that   
   >out.   
   >   
      
   I was doing what anybody would do when explaining a principle,   
   reducing it to its minimum implementation. It's what you do.   
      
   >   
   >>>>You cure it by turning down the amplifier so the sound from the   
   >>>> speaker is always a little softer than the original when it hits the   
   >>>> microphone.   
   >>>   
   >>>Or any other method that reduces the loop gain at the feedback frequency,   
   >>>notch filtering being a common example.   
   >>>   
   >>   
   >> Again, given the question, no need to complicate the answer.   
   >   
   >Or simplify it to the point of being wrong. To paraphrase Einstein, things   
   >should be as simple as possible, not simpler.   
   >   
      
   Simplified to the point of being wrong? Hear feedback, turn the gain   
   down until it stops. You are going to have to explain what is wrong   
   here - clearly I'm being thick.   
      
   d   
      
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