On Sat, 01 Feb 2014 16:52:23 -0800, Salmon Egg   
    wrote:   
      
   >In article ,   
   > Fred McKenzie  wrote:   
   >   
   >> In article ,   
   >>  Salmon Egg  wrote:   
   >>   
   >> > Why does placing a finger over a microphone improve the   
   >> > intelligibility?   
   >>   
   >> Salmon-   
   >>   
   >> I don't know about hearing aids, but it works for telephones in a noisy   
   >> environment.  Placing fingers over the mouthpiece reduces background   
   >> sounds that are fed back to the earpiece as "sidetone".  (Sidetone is   
   >> the percentage of your voice that goes back to the earpiece to let you   
   >> know the phone is working.)   
   >>   
   >> Fred   
   >   
   >I was thinking about that and asked the last person who fiddled with my   
   >hearing aids about side tone. He, of course, did not know what sidetone   
   >was.   
   >   
   >Although sound although sound is a longitudinal (scalar) pressure wave   
   >in the air, the theory has much similarity to that of antennas. I have   
   >never heard talk of multipath problems with hearing aids. I do not   
   >understand how two small microphones space a small fraction of a   
   >wavelength apart can be processed to give directional patterns. U can   
   >understand that spacing BETWEEN ears can give rise to interferometric   
   >cues. When I asked if the two aids exchange audio information, the   
   >answer was no.   
      
   We've been working with phased microphone arrays recently.  It was   
   amazing to see that the recommended spacing for one solution was 11mm.   
   You're right, it doesn't make much sense, given common knowledge of   
   antennas.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)