It seems like something to do if you only have one set of headphones you use with the amp. Are there reasons not to? And what do you get frmo impedance matching?

Thanks

I too would like to know this. Seems like a curious idea.

In general an amp should have VERY low output impedance as close to 0 Ohms as possible. If that is not possible (as with transformer/tube output) it should match the impedance of the headphones. Again if even that is impossible, it just shouldn't be higher than the headphones.

Any output impedance on the amp creates a voltage divider with the headphones and changes their frequency response. That's not something you generally want.

impedance "matching" is somewhat of a misnomer, at least in relation to audio gear. trying to match the impedance values between all pieces of gear would be highly unfeasible and difficult to do. one should only make sure that the output impedance of a component is lower than the input impedance of the next component in the chain.

since nearly all gear is designed with this in mind anyways, it's not really an issue.

You likely need an EE to explain this to you in the technical context.

However, from a practical standpoint (some of the comments below are accurate) amps with low output impedance will typically provide more current output to properly drive low impedance phones and control their drivers much better than amps with high impedance output.

Similarly, if you want the amp to also drive high impedance phones well, you want an amp that also provides high voltage output, which is typical of amps with a high impedance output.

Ideally, you want an amp that provides both high current output to drive low impedance phones and high voltage output to drive high impedance phones. This seems to be more typical of SS amps, and less typical of tube amps, except for the "better" tube amps, which often seem to provide both.

For example - The Woo Audio WA3 (OTL tube amp) provides plenty of voltage output to drive high impedance phones well, but does not provide sufficient current output to drive low impedance phones well. The X-CANv8 (tube / SS hybrid) provides plenty of current output to drive low impedance phones very well, but strains a bit to drive high impedance phones. The DV332 (OTL tube amp) provides plenty of voltage output to drive high impedance phones very well, and has pretty good current output to drive low impedance phones fairly well - it is unusual in that it is a "value priced" tube OTL amp, which drives both high and low impedance phones pretty well, as does the DV337 (its big brother).