Cheap Resonance Tube Powder

After cleaning out the powder from the P.H. resonance tube apparatus, after not being used in two years due to the lockdown, replacing the dust/powder became a mildly costly (£10 for 10g) potential issue. Philip Harris doesn't even appear to sell the replacement powder, only finding Breckland with it listed for this purpose at the cost of £1 per gram.

Suggestions for the powder are Mica, Lycopodium or Cork dust. It has to be light and fine, so things like talc aren't terribly suitable.

Some miniature/railway stockists sell fine cork for flocking, but the grade looked broad from powder to 1mm chunks in the same bags.

Cork dust, it struck me, how could I just make some....

5 min with a cork bung and some glass paper later I had 15g of fine powder with the odd large chunk (not a massive issue, I can sieve them out)

I'm quite pleased with my money saving tip that cost only time and an old cracked cork bung.
 
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Nick Mitchener

COMMITTEE
In the 2 metre tube I made I used expanded polystyrene beads from an old bean bag. I used your technique for my prototype that I made with a large measuring cylinder to show what I wanted the money for.
 
In the 2 metre tube I made I used expanded polystyrene beads from an old bean bag. I used your technique for my prototype that I made with a large measuring cylinder to show what I wanted the money for.
I've got some unexpanded polystyrene 0.5mm beads, they sorta worked, but the volume had to be maxed, and that is unpleasant to many to endure and hear the teacher explain the science. Did the expanded beads work full size, or did you have to grind them up to a powder?
 

Nick Mitchener

COMMITTEE
The expanded beads worked full size. When I first built it they would form little waving walls but that required ear defenders. I attenuated it by putting cotton wool in the box that held the speaker, now it can't get loud enough to need ear defenders but the little walls have gone. The beads clump nicely and you can work out the wavelength and the speed of sound if you know the frequency. (smart phone and phyphox)

The only thing I needed to modify but left before I did was the static build up in the tube. I was thinking about running aluminium tape down the tube and earthing it. Other wise it can take a couple of days to clear.
 
Our tube has polystyrene in it. They make little walls in the middle without it needing to be too loud although the teachers did manage to kill the speaker last year...
 

Nick Mitchener

COMMITTEE
Our tube has polystyrene in it. They make little walls in the middle without it needing to be too loud although the teachers did manage to kill the speaker last year...

How big is your tube? I think the one I made was 2metres long 100mm diameter. It did get very loud before I attenuated it.
 
How big is your tube? I think the one I made was 2metres long 100mm diameter. It did get very loud before I attenuated it.
It lives on top of a double Gratnell shelving rack so slightly shorter than that - I'm stuck at home at the moment awaiting a PCR result so can't measure!
 
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