The radio detection technique has successfully been applied to the measurement of cosmic-ray induced air showers with energies above 10^16 eV. A majority of these measurements are performed in the frequency band of 30-80 MHz, by the existing radio air-shower experiments. Recent results of a simulation study with CoREAS show that the optimisation of the frequency band improves the signal-to-noise ratio. This in turn lowers the energy threshold of detection by an order of magnitude. This talk will focus on the universal application of such a frequency optimisation for all future radio air-shower arrays, which will improve the performance of these future arrays. For this, a simulation study performed for the locations of IceTop, GRAND and the Pierre Auger Observatory using air showers generated by cosmic rays, gamma-rays and neutrinos is utilised.