How about double or triple glass with inner space(s) filled by water and/or special clear "snake oil" or "snake solution"?
I am a Ph.D. scientist as well as a "Certified Class-1 Radiation Protection Supervisor" (yes, I am serious, one of the most highly regarded difficult-to-get Governmental official certificates), and I know well that high-density ZnBr
2 (zinc bromide) clear aqueous solution (around 45g/100ml) can be filled in thick glass case for radiation (gamma, beta, and alpha) shielding; it is a really heavy, high-density clear liquid.
But,,, if the speaker glass case filled with ZnBr
2 solution would be broken by accident or earthquake, then....