def total_loss_factor(frequency, reverberation_time):
    """
    The total loss factor can be related to the reverberation time for any subsystem.
    
    :param frequency: Frequency :math:`f`.
    :param reverberation_time: Reverberation time :math:`T`.
    
    :returns: Total loss factor.
    
    .. math:: \\eta = \\frac{2.2}{f T}

    See Craik, equation 1.19, page 9.

    """
    return 2.2 / (frequency * reverberation_time)