Resonator material and tube length??

Hello Folks-

I’m a percussionist of many years who lucked into a fine old Deagan model 330 “Stu-Dette” marimba, a tiny one for sure at 2.5 octaves.

The bars are in fantastic shape, I will probably replace the grommets too but the big issue was this: the resonators are cardboard and it was missing the tubes (broken off) for the low C# and D#.

I’m a fix it guy, I do repairs on all sorts of instruments so I thought this would be fun to tackle.

I found 2 cardboard tubes the right diameter, I cut some aluminum caps for the bottoms, and I found a formula online for measuring resonator length for each pitch. I even found some paint that closely matches the paint on the other tubes.

Got it all together….the two replaced resonators aren’t quite as resonant.

Is it the cap on the tube? Should it be brass? Should the insides of the tubes be painted to be more reflective (this I thought of after I glued the caps on so I could only paint about half of the inside)? Should I use PVC or something as a reso tube? Or, could my calculations be off?

My resonators measure 30.8cm for the C# and 27.6cm for the D#.

Any leads would be great!

thanks

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