Any plan to try and play audio through the Arc and a 3rd party audio system at the same time is going to run into syncing issues.  

If the audio quality isn’t to your liking, either lower mid range or otherwise, I would redo trueplay tuning, or turn it off entirely, to see if this improves things in your opinion.

Thanks for the reply. I did retry the TruePlay tuning as per your advice and it did help to some extent, although the 100-500 Hz range is still pretty much lacking, even at normal listening volumes. I’m guessing the TruePlay adjusts volume levels and EQ profiles of the speakers, which in itself makes sense. On this topic, I wished there was an “expert mode” or similar where manual adjustments could be made with more precision than the Sonos Treble / Bass EQ. But if there’s no output to adjust, that point becomes moot.

The Sub Gen3 apparently crosses over at about 80 Hz. This leaves the Arc with the daunting task of covering 80 Hz and up. In my mind, one would need at least 8” bass reflex speakers to do a decent job in the high bass-low mid range. I just can’t wrap my head around why Sonos decided to leave this part out of the equation without offering any add-ons or solutions. If radio bandwidth is the issue I’d suggest simply offering a bigger soundbar that is up to the task.

Part of my frustration is that I went from a great sounding custom big-speaker setup to Sonos Arc mainly because of aesthetic concerns forwarded by my wife. While understanding the imminent compromise in sound output per speaker I was hoping for an acceptable middle way. We have had two Ones + a Sub Mini in the kitchen that I still think sound perfectly fine and so i jumped into the Arc + Sub + Era deal with a great deal of enthusiasm and a significant lack of precaution.

I am a bit of a perfectionist when it comes to sound - but have never felt the Arc has any of the frequency issues you mention. You seem someone who understands it all anyway, but a few things/questions/pointers:

Is this mainly on music, or TV, or both? (If TV, are there any settings you can adjust on the TV itself, or the set-top box etc?)

Make sure Night Mode and Speech Enhancement are both off. Both can ruin the Arc’s middle frequency balance. 

What level are the surrounds at for TV and Music? Try adjusting the surround TV level up and down, as a quieter surround will mean a louder Arc (higher volume needed overall which can affect the Arc’s middle), and vice versa. And adjust the Music level too, to balance things out. I’d also advise setting Music to Full rather than Ambient for a better balance when playing music. But again, your preference. 

What level have you set the Sub at? The sub takes the heavy bass lifting away from the Arc to allow the Arc to focus on the rest. If the sub Ievel is too high, this can leave the Arc a bit flat in my view. If the sub is set too low, this can cause the Arc to need to do many jobs, which can muddy the sound. 

Maybe your ear is more attuned, and none of this will make the required difference. But just some suggestions from experience...

Turning off night mode would be one solution to the issues, but speech enhancement is in the 100-500 Hz range, so I would suggest @Oscar7701 turn that on. I have speech enhancement  on all the time with my HT setup, because most automatic EQ settings that manufacturers provide, tends to cut the mid frequencies. This is because most people like the “smiley face” EQ setting for audio. 

I also keep my settings mostly flat, with the bass at 0 and treble at -2 ( the Arc’s high frequency tends to be a bit harsh, unlike the Playbar), Sub audio at 0 and surround audio at -2 for TV and -1 for music. Since there is no way to control the separate channels in the the Arc (except the height channels) the way you are able to for the Sub and surrounds, These settings are satisfactory for my listening needs. This way, for me, the Arc shines.

I must say, it’s nice to be in a thread that isn’t complaining about the new app…!

Thanks for all the suggestions, here’s an update. I redid the TruePlay tuning, holding my iPhone farther away from the front than I did the first time. Instead of walking around too much I just waved it a bit left and right about an arm’s length behind my listening position. This seems to have yielded a different result and now the EQ is better balanced overall. The front channel is still weak but some of the higher frequencies are not as annoying as they were. It’s not perfect but it’s decent. I also turned on the “Dialog” sound setting on the TV (Sony X90K). I’ll do some sweep testing later with a spectrometer, but at this point I can probably live with it as is.

While I’m sure TruePlay tuning is great when it works, I can’t help feeling that I’d rather want to be able to tune levels and EQ manually for each speaker. Not likely to ever happen, but one can hope. Also, if one could dream, allowing for an additional front speaker (or even an AUX OUT for the front channel on the Arc) would be a game changer.