  We present multi-frequency scatter broadening evolution of 29 pulsars
observed with the LOw Frequency ARray (LOFAR) and Long Wavelength Array (LWA).
We conducted new observations using LOFAR Low Band Antennae (LBA) as well as
utilized the archival data from LOFAR and LWA. This study has increased the
total of all multi-frequency or wide-band scattering measurements up to a
dispersion measure (DM) of 150~pc\,cm$^{-3}$ by 60\%. The scatter broadening
timescale ($\tau_{sc}$) measurements at different frequencies are often
combined by scaling them to a common reference frequency of 1\,GHz. Using our
data, we show that the $\tau_{sc}$--DM variations are best fitted for reference
frequencies close to 200--300\,MHz, and scaling to higher or lower frequencies
results in significantly more scatter in data. We suggest that this effect
might indicate a frequency dependence of the scatter broadening scaling index
($\alpha$). However, a selection bias due to our chosen observing frequencies
can not be ruled out with the current data set. Our data did not favour any
particular model of the DM -- $\tau_{sc}$ relations, and we do not see a
statistically significant break at the low DM range in this relation. The
turbulence spectral index ($\beta$) is found to be steeper than that is
expected from a Kolmogorov spectrum. This indicates that the local ISM
turbulence may have a low wave-number cutoff or presence of large scale
inhomogeneities in the line of sight to some of the reported pulsars.
