Impedance matching

To S. Andrea Sundaram,

I've been a reader of the SoundStage! Network and its publications for years and wanted thank you for all the wonderful articles and gear you've taught me about that I never would have come across otherwise. That being said, I do have a question. How important is impedance matching of audio components, and could you give a quick general rule or idea of how to go about impedance matching components when shopping for new gear?

Isaac Dahan

Impedance matching can imply different things in different contexts. I'll briefly cover the two most common applications in audio.

1) Speakers and amplifiers: A speaker's impedance can vary widely with frequency. When the speaker is driven by an amplifier having a high output impedance -- most tube amplifiers fall into this category -- the frequency response of the speaker will be modified. If you are using a tube amplifier with multiple output taps, you want to choose the taps that are closest to the impedance of your loudspeaker over the widest range. (You can usually go by the nominal impedance, but that really depends on how it was calculated.) Using a 4-ohm speaker with 8-ohm taps could harm the amplifier, and probably won't sound very good. Most solid-state amplifiers have a low enough output impedance to drive any speaker rated 4 ohms or above.

2) Sources, preamplifiers, and amplifiers: Impedance matching for these components can be trickier, because the necessary information isn't always published. Ideally, you want a low output impedance going into a high input impedance. That arrangement usually leads to a system with good stability and low distortion. Most sources will work well with any preamplifier or integrated amplifier. Some may have trouble driving an amplifier directly or through a passive volume control. Choosing preamplifiers and amplifiers from the same manufacturer usually eliminates any potential problems there, but combinations of equipment from different manufacturers can still work well together. Here's where a knowledgeable dealer would be an asset. . . . S. Andrea Sundaram