audioguru is right,(as usual,that's why I dedicated a video to him on youtube) It's important to match your speaker impedance to your set,if you have a speaker impedance of say,8 ohms & the set is rated at 4 ohms,the speaker will lose some of it's efficiency.However,if the impedance were mismatched the other around,then not only will efficiency suffer,but there is the possibility of damaging the unit.eg;two 4 ohm speakers in parallel will result in 2 ohms impedance,whereas two 4 ohm speakers in series results in 8 ohms impedance.If the terminals of the speakers are not marked +&-,you can check them with a 1.5 v battery.If the "cone" moves inwards,then you have found the right polarity,if it moves outwards,then it's wrong.