[LAD] A little quiz about audio measurements...

[Gene Heskett]

On Saturday 29 May 2010, Ralf Mardorf wrote:
[...]

>I found no Wiki for "Überferquenz", increased frequency. At what value
>was the voltage, when there were 100 Hz?

The 100 HZ component is what you get by rectifying both halves of the sine 
wave, effectively inverting the lower half to become another pulse, with 
lots of distortion so there will be harmonics of the 100HZ also displayed on 
the spectrum display.   In most power generators, the voltage at the output 
is regulated by the current through the rotating armature being controlled, 
so the voltage, should the armature overspeed, is generally fairly stable.

In what we call standby power systems here, the throttle of the engine doing 
the turning is usually controlled by the output frequency, with a drop in 
frequency being assumed to be an increase in the load, and an increase being 
a drop in the load, generally achieving about a +- 1 hz tolerance.  In much 
larger systems, there will be a fixed frequency reference derived from a 
master clock, and the phase angles of the power are compared to this 
reference, with a very high gain so the phase errors are usually within a 
degree.  So the system is said to be phase locked.  The input energy to turn 
the machinery, water gates, whatever, are where the control is actually 
exerted.  Should any one 'generator' get more than a few degrees out of 
lock, it will usually disconnect itself, or reduce its excitation current to 
allow it to catch up or increase it if it needs to slow minutely, this may 
cause a few millivolts of a voltage change to the whole grid.  Somewhere in 
here the load shedding also comes into play if it is a controllable item for 
that section of the grid.

Where the grid idea fails in places like the US, is when the light speed 
propagation delays begin to play with the phase reference.  Because of this 
the USA is broken into smaller pieces grid wise.

>So if anybody wants to program a virtual Hammond B3, should he take care
>about tuning effects caused by the power line?
>Btw. is the motors speed for a B3 depending to the voltage or is it
>synced by the frequency?
>
>Ralf

They are synch motors Ralf.  Its a different motor for me at 60hz on this 
side of the pond.


-- 
Cheers, Gene
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