Due to the increasing popularity of lightweight building methods, vibrations and low frequency noise have become a greater challenge. This work deals with the assessment of impact noise at the 31.5 Hz octave band. Three possible impact sound sources to determine the sound insulation have been tested and compared in laboratory measurements. It is concluded that the excitation using the rubber ball, as described in Annex F of ISO/DIS 140 part 11, is comparable to that from using the heel-drop method. The latter is described in the Dutch SBR guidelines for walking inducedfioor vibrations. It is further concluded that the standard hammerbox excitation method, generally used for the assessment of impact sound insulation above 50Hz, is not suitable for the lower frequency range. Due to the possible pronounced modal character of the soundfield in the receiving room, it is recommended to introduce the L10 sound level: the sound level that is only exceeded in 10% of the room volume. As it has been proven with extensive tests on human subjects, the A-weighted sound level can be used for the assessment of most sound sources. However, in particular cases penalty factors have to be taken into account.