Physics 01
What Is the Highest Frequency Humans Can Hear?
The textbook says 20 kHz, but in a 2021 study only 52 % of ears under 30 heard it and none over 50 did. Here is what ages each band and how to test yours.
acoustics
Electronics 02
Why 3 dB Is Double the Power (and 6 dB Double the Voltage)
3 dB is double the power because 10 log 2 = 3.01. Why voltage needs 20 log, why two 80 dB speakers make 83 dB, and how dBm, dBu and distance work.