It'll work fine. At audio frequencies the impedance characteristics
of the coax are unimportant over this short distance.  Just make
sure the plastic sheath is in good condition so there is no
leakage to ground as this would unbalance the two wires (called
'tip' and 'ring') to ground which balance is very important.  If you
have a digital multimeter measure this resistance of both sheath and center conductor to your house ground.  If over
ten megohms (the test standard) you will be fine.   If less, you
might get some hum.