Putting weights on speakers?

I now have put 53 pounds on each speaker.
They are OB on the mids  and tweeters. And have a back enclosure for the woofers. So I am able to just put weight on the woofers however I notice increased clarity on all frequencies. Especially tightening up the lower ones. And the imaging is much better. I would highly recommend weights on speakers. For WAF Rougefitness.com sells pairs of black vest plate weights for $56. I bought and am using 4 pair, 4 on each speaker.
But increase from 33 pounds (8.75 lbs each plate) to 53 lbs is a great increase in clarity. I hear no down side to the extra weight. The additional 20 pounds come from 20 lb ankle weights. They spoil the WAF but since they are in back hope the wife does not notice!

Up date,
I took 20 lbs off each speaker leaving 33 lbs on each. The bass is more complex and still tightened. Works better with less weight.
The extra 20 lbs deadened the bass too much!

Anything that touches the cabinets will change the sound.  If you want a more elegant solution try HRS damping plates.  www.avisolation.com

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.