>"O'scope, separate mics, two channels?  "   
      
   Seems like a bit much.   
      
   >"I wonder how speaker phase affects our perception of sound.  Assume both   
   speakers are phased to each other.  Now can human hearing discern when they   
   are phased correctly for the program material?  I can't, but maybe there are   
   people who can. "   
      
   Very few people can. They did pay attention to phasing on AM radio because   
   they would rather "up" modulate than "down" modulate. There is also a   
   difference in some speaker systems. Some. Also amps with single ended output.    
      
   >"And what happens in a orchestra... the wind section, for instance,   
   takes great pains to see that they are all playing the same note   
   frequency-wise before the concert starts, but surely some slight   
   variations on timing must cause one or the other to be phased slightly   
   different from the rest of the section. "   
      
   Part of the confusion there is that those fucking stupid schools used to teach   
   that a 180 phase shift is the same as inversion. That only applies to   
   symmetrical waveforms like a sine or 50 % duty square, or triangle. (not a   
   sawtooth) Anything that has a    
   mirror positive and negative side. Many instruments do not, and I mena really   
   do not.    
      
   How much of that you can actually hear is a question. For example to reproduce   
   a muted trumpet to real levels requires thousands of watts because of crest   
   factor and whatever. It is definitely non symmetrical. So is the human voice,   
   which may explain the    
   fact that people will tolerate low even order distortion to higher levels than   
   other types.    
      
   So when they talk abut speakers being out of phase they don't REALLY know what   
   they're talking about. what that is when the speaker wires are reversed on one   
   is INVERTED.    
      
   Many people can tell when speakers are out of phase with each other. I can,   
   and on fact have been called upon to phase multiple or "stacked" speaker   
   systems. This is needed because speaker polarity is not standard between   
   manufacturers nor even among    
   models of one manufacturer.    
      
   Some are more sensitive. Many years ago I sis audio at Wellman & Griffith. In   
   was a Sansui receiver with DC coupling but no DC protection. One of the   
   transistor sockets went intermittent and blew both woofers in an EPI. It had a   
   switch for 4 or 16 ohms    
   and of course it was set to 4, so both woofers went. I had some used ones and   
   sold them to the guy and installed them at the company. There was another   
   audio guy there and he listened and said "There is no center". Sounded fine to   
   me, but when you work    
   at a high end place thing need to be done right, so I got the customer to   
   bring in the other speaker. Sure as shit, the woofers were out of polarity and   
   that guy could hear the difference. When I hooked up both speakers they   
   definitely sounded out to me,    
   but I couldn't tell woofer from tweeter he could. I had observed polarity at   
   all times and the woofers were actually wired the other way. I reversed the   
   wires internally and all was well.    
      
   Not only did the speaker we fixed sound fine to me, I couldn't hear the   
   difference between it and the one that was right.    
      
   Some people can't hear the difference at all unless they are right next to   
   each other, or on the same cabinet. One place you could really tell was in old   
   cars that had a pair of speakers (6X9) in the rear deck. I have literally   
   insisted someone STOP THE    
   CAR, GIVE ME THE TRUNK KEY. Why ? Just do it. I crawled in the trunk and   
   reversed the wire son one speaker, got back in and said go ahead. They turned   
   the stereo back on and said "Damn, what did you do ?".    
      
   Even for me, if the speakers are far apart  it can be hard to tell. The bass   
   is not mixing so if it is out of polarity it makes so little difference   
   sometimes it just isn't worth the trouble.    
      
   Absolute polarity is a difficult thing. You must be sure, for example, that   
   the microphone(s) put out positive voltage when air is PUSHED to it/them. Then   
   EVERY step in the process, this means tape heads, the cutting lathe for the   
   master recording to the    
   phono cartridge to the pre amps and amps and the speaker all must not reverse   
   the polarity. That is damn hard to guarantee. In digital, if the OP AMPs in   
   the filters invert, it must be reinverted.    
      
   It's a big pain in the ass.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)