Are you talking specifically about powered speakers? Certainly, resistance is a lesser concern when you’re passing almost no current.

But it’s important to have a heavy enough gauge cable between amplifiers and passive speakers so that there is not too much resistance, as this will cause it to overheat and potentially start a fire.

Generally speaking, I think a coat hanger’s gauge is too small for common amplifiers. Plus, if it’s iron then it’s going to have a higher resistance compared to standard materials, meaning more voltage drop and more heating.