ISO plans to replace the current ISO 140-7 standard for the measurement of impact sound pressure level by a new standard, ISO 16283-2. Within the standardization work, we have examined the influence of the position of the tapping machine (TM) on top of a timber joist floor (built as the reference light weight floor 2 in ISO 10140 and the previous ISO 140-11). The question is whether it is sufficient to prescribe that the TM positions shall be randomly distributed over the floor area (as in ISO 140-7) or if they should be specified to hit the joists with one hammer (as in ISO 10140) or even hit the joists with all hammers. The room average sound pressure level was measured with 63 evenly distributed TM positions on the floor, either on top of a joist or on the web. The influence of the TM position relative the joists is rather stable at low frequencies (25-160 Hz). Having the TM at right angles to the joists and one hammer striking a joist, the average difference is 3 dB to when no joist is being hit. Comparing positions where all hammers hit the joists with positions in between the joists, the difference is typically 4-7 dB in the frequency range 25-160 Hz. The results indicate that the ISO 16283-2 could prescribe more precisely where the TM shall be positioned in order to reduce the random variations. One choice is then to follow ISO 10140-1, where the TM is placed at 45 degrees centered on the joists, such that one hammer strikes a joist.