def unapply_spherical_spreading(signal, distance):
    """Unapply spherical spreading.

    .. math:: p_2 = p_2 \\frac{r_1}{r_2}

    where :math:`r_1` is 1.0.

    :param signal: Signal
    :type signal: :class:`auraliser.signal.Signal`
    :rtype: :class:`auraliser.signal.Signal`

    """
    return signal * distance