conditions for "far field":
1. d >> l
2. d/l >> l/wavelength
3. d >> wavelength

given l = 1, d = 10
10 >> 1, condition met
10 >> 1/wavelength, valid for wavelength > 0.10
therefore, f2 = c/wavelength = 3400.00
since if d is to be >> wavelength, and d is fixed, wavelength can increase to a maximum of 10.00, so f1 must = c/d = 34.00
frequency range of operation of the array is approximately:
   34.00 Hz < f < 3400.00 Hz