def _meco_frequency(m1, m2, chi1, chi2):
    """Returns the frequency of the minimum energy cutoff for 3.5pN (2.5pN spin)
    """
    return velocity_to_frequency(meco_velocity(m1, m2, chi1, chi2), m1+m2)
Returns the frequency of the minimum energy cutoff for 3.5pN (2.5pN spin)