You don’t need to be Einstein to get this right, but before buying a thing, you do need a vocabulary lesson. These are the key terms used in speaker and amp specs that are critical to your search for good synergy and great sound.
First up, Impedance. Impedance starts with I, just like important. Used in both amp and speaker spec sheets, impedance is a measure of the electrical resistance of your components. It’s measured in ohms and is often represented with the symbol “Ω”—as in 8Ω. This is part of the equation in determining the synergy between your speakers and amp. Speakers typically carry ratings between 4 and 8 ohms. Amplifiers generally operate effectively in a specified range: say, 4 to 16 ohms. Check your specs, but when that’s the case, connecting a speaker rated between 4 and 16 ohms will be OK.
But—and this is where it gets more interesting—you need to be aware that many amps output different wattages into different ohms. (We’ll go into wattage in more detail below—for now, all you need to know is that it’s a measure of power). For example, NAD’s ridiculously popular D3045 stereo integrated amplifier outputs a continuous 60 watts per channel into 8 ohms and 4 ohms, but its Dynamic Power (sometimes called Peak Power, which refers to when it’s being pushed to its max) hits 80 watts into 8 ohms and 150 watts into 4 ohms.
Generally speaking, it’s fine to connect higher impedance speakers to an amp; what you don’t want to do is plug low impedance speakers, let’s say 4 ohms, into an amp that specifies a minimum 8-ohm limit. To take some math work and guessing out of the equation, a lot of speaker and amp manufacturers are switching over to using “compatible with” ohm ratings, which makes things a lot easier.