A great question and some interesting comments from my team. I think we need to carry out some experiments to test the ideas that my friends have.
Firstly we know that air can carry sound. To consider the radiator pipe idea we need to get a tube of metal and see if, on it’s own, it carries sound. tap one end of the tube and put your ear on the other end. record what you hear. Now fill the tube with water and repeat the experiment. You could also get a rod of metal, with no air, no water and test that. If you had a sound sensor(your school might have one) you could measure the amount of sound that a solid rod, water filled rod and air filled rod carry. Which was best? How did you make the test fair?
The string telephone could be another example of sound travelling from one place to another without using the air. Try to make ‘telephones’ that are ‘sound proof’. For example make sure that when somebody is speaking into the mouthpiece they cannot be heard speaking by those standing around. No ‘air’ sounds. to do this you might have to modify the mouthpiece.
Try this video for further information. If after watching it you have any further questions ….THEN