Mac mini very quiet rubbish sound for music with external speakers

I have a set of external speakers that I have used for years via mini jack plug in my 2015 iMac, with good sound. I have plugged the same speakers into a 2022 Mac mini with a USB adapter. The sound is muted and no base. I have turned the volume up to max in System Preferences (and everywhere else) and the sound is still rubbish. As the new and old computers are next to each other I can unplug the USB and put the jack back into the old iMac and the good sound is back at double the volume! Any ideas please.