Is using an instrument cable as speaker cable a cause for so much interference in my PA speaker?

I have mistakenly been using an instrument 1/4" cable into my PA system from a DI Guitar rig, and I'm wondering if this is a major cause of the excessive buzz and hum I'm getting from the speaker. Will using a proper speaker cable solve this problem? (I was told wrong information by the guy who gave me some cables)

Or is it just an inevitable side effect of owning a slightly cheaper PA Speaker (harbinger)?