From: jrwalliker@gmail.com   
      
   On 11/12/2025 12:14, Liz Tuddenham wrote:   
   > John R Walliker  wrote:   
   >   
   >> On 10/12/2025 23:06, Don Y wrote:   
   >>> On 12/10/2025 7:25 AM, Liz Tuddenham wrote:   
   >>>> Martin Brown <'''newspam'''@nonad.co.uk> wrote:   
   >>>>   
   >>>> [...]   
   >>>>>   
   >>>>> ISTR that in the Three Mile Island disaster they spent the first fifteen   
   >>>>> minutes of the emergency trying to silence all the different damn alarms   
   >>>>> that made it impossible to think in the control room. Only once they had   
   >>>>> the noise under control could they communicate with each other across   
   >>>>> the room.   
   >>>>   
   >>>> I worked in a university where they had just one sounder for each floor,   
   >>>> mounted at the end of a each corridor.  They had made it loud enough to   
   >>>> be heard in the laboratories with all the doors shut.  It would have   
   >>>> been safer to climb out of a window than enter the corridor and try to   
   >>>> escape past the sounder.   
   >>>   
   >>> You can get 200-300dB klaxon's relatively easily.  I had one in   
   >>> college that was "fun" (for some perverse definition of "fun")   
   >>> to play with.   
   >>   
   >> Are you sure about that?  200dB is a couple of atmospheres.   
   >   
   > Does this mean that the pressure during the negative half-cycles goes   
   > below a perfect vacuum or that the device doubles the average   
   > atmospheric pressure in its vicinity?   
   >   
      
   At about 191dB spl for a sine wave the lowest pressure will be a vacuum   
   and the highest will be two atmospheres absolute pressure.  Gases are   
   unable to go to lower pressures than a vacuum, so that is a fundamental   
   limit for an undistorted sine wave.   
   As the average pressure needs to stay at one atmosphere if the system   
   is in open air the only way to get more positive pressure while limiting   
   the negative pressure to zero is to narrow the positive half cycles   
   to pulses.  Shock waves are produced.   
      
   Here is a video showing shock waves coming from the bell of a trumpet   
   and how they interact with various objects.   
      
   https://www.youtube.com/watch?v=adJEumpIN9M   
      
   John   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)