Abe is wrong; you can connect them in series and then you will have a 10-ohm load per side. It will be safer for the amplifier, but will not play as loud. In the series connection you would connect the positive amp terminal to a positive speaker terminal then the negative terminal of that speaker to the positive of the second speaker; then run the negative of the second speaker back to the negative amp terminal. This is probably best done with identical speaker pairs if they are being used in the same room. If you have two pairs of different speakers (and you do) and the efficiency of the respective pairs differs (likely) one pair will play louder than the other no matter which way you hook them up...