Whether or not speaker terminals are at "ground potential" (I ma not even sure where that is coming from actually), you can NEVER make speaker connectors touch as this is call a "short" and is usually followed by a huge series of clicks as your receiver goes into protective mode. So either your question needs to be formulated differently or you have nothing to worry about as these sub-woofers and something a million Ohms of resistance on those speaker terminals.

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