The Era 100 and Sonos One are not part of the same speaker family. Or is that what you meant - why are they not consistent between differing models of speakers?

Possibly it’s because the Era 100 is a stereo speaker by proper function, so going mono on it isn’t meant to match with the previous models. 

Understood, I realize that there are two separately-driven tweeters, but shouldn’t the common bass driver be phased with the same polarity as the other Sonos speakers? Otherwise, multiple speakers in different nearby areas will cancel partially at low frequencies, which are fairly non-directional. Am I not supposed to mix different speaker generations in the same acoustic space? If so, shouldn’t Sonos caution customers about that in their sales info?

I don’t think there is any ‘polarity’ settings for regular speakers, only for Subs, when added. I have always assumed the polarity was set by the software to correspond with the other speakers in the system, in which ever fashion is appropriate. And more so (if that is possible) for stereo paired speakers than merely grouped speakers. 

In your case, I’d be tempted to try a couple of things, since they are two different models, and can’t be stereo paired. The first, and easiest, would be to simply power cycle the Era 100. And frankly, while it was powered off, I’d see if there was more bass perceived from the Sonos One. It might potentially be that the Era 100, being both newer and slightly larger, puts out more bass. 

If that doesn’t help, I’d probably factory reset just the Era 100, and not the Sonos One. Then re-add the Era 100 to the system, and see if it properly picks up the polarity you think is missing. 

But, if neither of those achieve the results you’re looking for, I would call Sonos Support directly to discuss it.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

“Phase” is a way of expressing the time relationship between two audio signals. Typically, we express phase at a particular frequency. I can imagine that the processing latency is slightly different between different models of online players. Therefore, even if the networking is adjusted such that the network data is delivered to each speaker in sync, different audio processing delays in different models will mess with “phase”.

As an experiment face two samples of the same model towards each other as close as possible, but without touching. (playing a mono or same channel feed) Here you will get maximum phase cancellation -- especially in the bass because the spacing between woofers is a very small fraction of the wavelength that the woofers cover. Treble cancelation will not be quite as complete because of the wavelengths. Next, face two different speakers. Don’t expect the same degree of cancellation that is achieved with identical models, but I would suspect a phase difference if the speakers need to be separated somewhat before an obvious cancellation is observed. Dual tweeters, one on each side, make this face to face confrontation difficult to interpret with respect to phase.

Hi, buzz, you describe a test I have done many times and also did with the two speakers in question. Theoretically, facing two identical speakers together, playing the same material at the same level, will NOT produce bass cancellation, but reinforcement, raising the sound pressure level at frequencies with wavelengths much larger than the separation distance by 6 dB over having only one speaker playing. If, however, one speaker has inverted polarity, due to being incorrectly wired, your will have severe cancellation. In the case of the One versus the Era 100, when I faced them together, I heard more bass when I muted on or the other than when both were playing, indicating some degree of cancellation. But I did reach out to Sonos, and though they could not account for this, I do plan to test all my Sonos speakers with a polarity-checking instrument that indicates the acoustic polarity of a unipolar pulse signal, and report back to them. It’s possible that the different families of Sonos speakers are not polarity-synchronized, due to either acoustic or electrical processing design differences.