When solving a model in the frequency domain, you need to specify the Frequencies to solve for in the Frequency Domain study step. Several built in options exist when selecting the Range (). Specifically for acoustics modeling the Entry method has the Logarithmic and the ISO preferred frequencies. The latter option is only available with the Acoustics Module and is activated by clicking the Show button () and select Advanced Study Options. For ISO preferred frequencies, select a start and stop frequency and the interval (Octave, 1/3 Octave, 1/6 Octave, 1/12 Octave, and 1/24 Octave). The 1/3 octave preferred frequencies are defined based on ISO 266. They are extended to frequencies based on the preferred numbers of ISO 3 (series R20, R40, and R80).