  Here we present a detailed study of the THz and FIR response of the mixed
perovskite manganite system Eu$_{1-x}$Ho$_x$MnO$_3$ for holmium concentrations
x = 0.1 and 0.3. We compare the magnetic excitations of the four different
magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated
collinear, helical phases with spin planes perpendicular to the
crystallographic a and c axes). The transition between the two latter phases
goes hand in hand with a switching of the ferroelectric polarization from P||a
to P||c. Special emphasis is paid to the temperature dependence of the
excitations at this transition. We find a significant change of intensity
indicating that the exchange striction mechanism cannot be the only mechanism
to induce dipolar weight to spin-wave excitations. We also focus on excitations
within the incommensurate collinear antiferromagnetic phase and find a so far
unobserved excitation close to 40 cm$^{-1}$. A detailed analysis of optical
weight gives a further unexpected result: In the multiferroic phase with P||c
all the spectral weight of the electromagnons comes from the lowest phonon
mode. However, for the phase with the polarization P||a additional spectral
weight must be transferred from higher frequencies.
