Can I hook up speakers without using the ground?

I accidentally hooked up some speakers using the 4 0hm tap for the positive run but accidentally connected the return to the 4 ohm tap instead of the common/ground.

I didn't damage anything but I didn't leave it connected that way long. It had some interesting sonic effects that I did not take the time to explore out of caution. The hook up reminds me somewhat of the hook up you used with the old David Hafler design for pseudo quad set ups rear speakers.

The amp is a Mesa Barron dual mono. Speakers are 3 way dynamics with very expensive tweeters ergo my caution.

Is there any short range or long range risk doing this?