Some simple facts that you can carry in your head
The speed of sound is roughly one foot per millisecond.
So at 1kHz, a single wave is about one foot long. At 500Hz, it is two foot long. At 250Hz it
is 4 ft. At 125Hz, it is 8 ft long - and so on.
Middle A is 440Hz.
You can calculate beats per minute with stop watch and count off four bars, starting and finishing on the
'one.' Call the time taken by those four bars T then the calculation is
16 / T x 60 = bpm
So if we tap off 16 in eight seconds, then 16 / 8 =
2 and 2 x 60 = 120.
If we tap off 16 beats in 10 seconds, then the calculation is
16 / 10 x 60 = 96bpm.
Voltage is Current times Resistance (V = I x R)
The Power Law
Power is Voltage times Current (P = V x I)
so Wattage is Voltage multiplied by Ampage.