This is a question we get a lot and for most applications, we have a simple solution. We have actually created a line of our hemispheres that are coated with a urethane coating to help protect the surfaces you put your speaker on. The main thing to realize is that the size of the speaker is not as important as the weight of the speaker. You want the Isolate It! Hemispheres to be compressed about 10%-15% for best results.  To keep things simple we are going to always use 4 hemispheres per speaker 1 in each corner of the speaker. You can also add a 5th hemisphere in the middle if it helps you achieve a more accurate load rating.

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Example: 

48lbs speaker 

48/4 = 12lbs 

Use the 1.5" hemispheres that have a weight loading of 7-14lbs.  

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We have done some of the calculations for you based on putting 4 hemispheres under each speaker. Again you want your speaker to be as close the middle of the weight loading as possible for example if your speaker weights 30lbs you would want to 1.25" hemispheres that have a weight loading of 20lbs-40lbs and not the 1.50" hemispheres that have a weight loading of 28lbs-40lbs.