All speakers are not the same and some caution is advised. 8 ohms, 16 ohms, etc. is the impedence of the speaker. It's an important number if you start to approach certain wattage factors that you may be outputing from your source. If you put speakers in series, the impedence adds up. If you put speakers in parallel, the impedence divides up, so more current can pass thru the speakers and burn 'em up. So, if you have a 16 ohm speaker on the ourput of something that normally would have an 8 ohm speaker, the volume is reduced. I think that's how it goes! If you have an 8 ohm speaker on something designed to handle 16 ohms, increasing the output (volume) could burn out the source by drawing too much current.
