Kundt's tube using standing wave ratio method

[FelliLoss]

Hello everyone. First i want to apologize if i cant write quite well, but english isn't my first language, but I'm trying to do my best effort

I want to design a Kundt's tube using standing wave ratio method, so i bought ISO 10534-1 for checking the tube conditions, but... when i read the "microphone conditions" i found it must have a "probe tube"

Could somebody explain to me what a "microphone with probe tube" is? can i buy a single microphone and later buy the probe tube or must it buy together like a "single measurement device"?

Thanks in advance!