  We have made the first phonon absorption measurements in the fractional
quantum Hall r\'egime. Experiments have been conducted on two samples which
have similar electron densities but greatly differing mobilities. The energy
gaps as measured by activation studies of the longitudinal resistance differ by
a factor of two. Phonon absorption measurements give almost identical values
for the energy gap demonstrating that the gap measured in this way is rather
insensitive to disorder. The value of this gap is in agreement with the
activation gap measured in the high mobility sample. Values obtained at
$\nu=2/3$ are in good agreement with theory.
