Whether you'll need to pay duty depends on where the speakers were made. If they're of U.S. or Canadian manufacture the NAFTA agreement means you won't need to pay an import duty. If they're European, or from any country outside the territory NAFTA covers, you'll pay duty.
It's important that you have documentation about the origin and value of the speakers when you come back into the U.S. Otherwise, you're at the mercy of what a customs officer thinks. You might be able to get through without declaring them but that puts you at risk if you do get checked.
It's important that you have documentation about the origin and value of the speakers when you come back into the U.S. Otherwise, you're at the mercy of what a customs officer thinks. You might be able to get through without declaring them but that puts you at risk if you do get checked.