Putting weights on speakers?

I have been having Mass loading custom  made tops for my speakers for years 
made of polished Granite exactly to the shape of the speaker  , I put a bit of blutac on top of  the speaker and placed the 
beautiful polished. granite on top not only does it look nice but the weight absorbs all the excess vibration which most speakers cabinets are not thst thick. I use a 1/2 Bull nose radius .which looks nice ,gives better focus and imaging for  under $200 per speaker money very well spent a very small investment per return in better musicality, A very small investment for reward in several ways,and your speaker looks even more elegant ,in any colors you choose ,and I matched my subwoofer in Black pearl,  
I made one for my dac also and put herbies feet underneath 

• the granite .
  

I bought a couple of fifty pound bags of play sand from Home Depot, put each in a nice pillow case which complements the room decor and placed one on top of each of my HT Tuba horn sub woofers which sit in sand boxes.  This is a very easy and fairly high WAF method of mass loading speakers.  More or less sand would allow fine tuning the arrangement.

For some simple, affordable experimentation, you can try some round metal doorstops that can be found on Amazon.  I have used them with success on speakers and on components.  There are several different sizes/weights, and they only run about $10-$15 each.  

https://www.amazon.com/Stainless-Stopper-Premium-SofiHome-Durability/dp/B01MFEC211/ref=pd_bxgy_img_3...