Heavy and stable base is needed for speakers placement. Go to granite cutting shop near you and custom order a couple granite plates. Avoid fancy expensive city stores cause it will cost you a lot, find some granite wear house outside the city line. I ordered my 20 x 20 x 1,5 inch plates $40 each, but it was years ago. Totally satisfied with the results. If you don’t want to go complicated way with custom order, Home Depot has pre cut granite tiles 18x18 inch, those tiles are not so thick and heavy, but also could do the job, I use them with great results for my components placement.