Both LEGO™ NXT sound sensors were placed at the
same distance from the speaker. A very simple LabVIEW
NXT toolkit was run in debugging mode, in order to display the values on the
PC screen and keep the NXT alive (Fig. 3). The frequency and the signal
amplitude were gradually changed and the sensor readings were noted manually and
entered into an Excel-file and also into a LabVIEW 3D-graph program (that we do
not reproduce here). (Fig. 4 and 5) show the different graphs in 3D for the
frequencies 100..1000Hz.