![I saw these at a music concert I attended recently. What are these large black rectangular tabs filled with water for that was placed on the ground around the speaker poles? : I saw these at a music concert I attended recently. What are these large black rectangular tabs filled with water for that was placed on the ground around the speaker poles? :](https://preview.redd.it/qhrh7pv91p891.jpg?width=640&crop=smart&auto=webp&s=8a3e39218c59ef7c4b2fb5ca86cad34efea74caa)
I saw these at a music concert I attended recently. What are these large black rectangular tabs filled with water for that was placed on the ground around the speaker poles? :
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