Remove the lid from the sound sucker container.  Place the speaker so that it just clears the top of the straws.  Adjust the frequency until the intensity diminishes.  ( Frequencies should be in the neighborhood of 660, 2000, and 3200 Hz. )  Position the microphone on the side opposite the speaker.  As you move the sound sucker away from this initial position you should see the amplitude of the waveform on the oscilloscope increase. 

The pipes with holes down the length have a “band gap” like a semiconductor due to the periodic holes.  In musical instruments like a clarinet it is called the “tone-hole cut-off”.   Tone holes are not periodic, but the effect is similar.