I have been playing around with PVC pipe speakers and found that toilet rolls seem to have an interesting damping property. Not sure what is going on but thought I would share it so others may like to experiment also and see if they have similar findings. It may become useful for tuning ports or something. The toilet rolls seem to drastically reduce the hollow tube sound. Adding rolls together seems ti make things better. Sure it increases the tube length and therefore pipe tuning resonance but it still seems to reduce the tube hollow sound quite dramatically.