A month ago, I bought a "Like New" Yamaha HS7 off eBay. I didn't have a cable to connect these to my computer until today when I got a 1/8 inch to dual XLR cable and connected them to my computer. I noticed that the monitors sound extremely different; one of them sounds relatively normal, maybe slightly trebly, while the other has next to no high end, sounds very muffled, and is significantly lower in volume as well. I found out later that the XLR output ends of the cable is unbalanced so that may be a source of issue, however even when I made the signal mono and used the same output, one of the speakers is always quieter and more muffled than the other. I've tried different combinations of mixing inputs/power cables/power source, but got the same result, which leads me to believe it's not the cable. Does this mean that this speaker is faulty, or could this be somehow caused by the unbalanced cable?
Thank you in advance for your answers.