  The knowledge of the origin and statistical properties of diffuse radio
emission in galaxy clusters has appreciably improved thanks to the GMRT Radio
Halo Survey, a project based on 610 MHz observations of clusters belonging to a
statistically complete sample. However, the spectral properties of cluster
diffuse sources are still poorly known and uncertain. High sensitivity and
multi-resolution observations at low frequency ($\le$0.3 GHz) are needed for
accurate spectral studies. Here, GMRT images at 325 MHz are presented for the
clusters A2744, A1300, A1758N and A781, all hosting cluster-scale diffuse
emission in the form of a giant halo and/or relic. These observations are part
of a new observational campaign to follow up with the GMRT at 150, 235 and 325
MHz all diffuse radio sources in the cluster sample of the GMRT Radio Halo
Survey and obtain detailed information on their radio spectral properties.
