Question 6.5: Determination of the Break Frequency for a Highpass Filter ,...

Recall that the low-frequency asymptote slopes at a rate of 20 dB/decade.
Thus, we must select f_B to be

\frac{30 \text{ dB}}{20 \text{ dB/decade}} =1.5 \text{ decades}

higher than 60 Hz. Employing Equation 6.17, we have

\begin{matrix} \text{number of decades}&=&\log\left(\frac{f_2}{f_1} \right) &&&&& (6.17) \\ \log\left(\frac{f_B}{60} \right) &=&1.5 \end{matrix}

This is equivalent to

\frac{f_B}{60}=10^{1.5}=31.6

which yields

f_B\cong 1900 \text{ Hz}