I’m  having the same issue with my sub3 connected to my Arc Ultra, and Era 300 surround. The subwoofer isn’t producing anything noticeable when connected to the Ultra.

Others have mentioned that if the Ultra is connected to ethernet and the Sub is not during setup, this may cause issues. I will see if a factory rest of all devices and a resetup fixes this issue with all speakers on WiFi.

Ok thanks for the feedback and please let us know !

I think resetting everything helped. It still isn’t quite as boomy as before but significantly better than my initial issue when I couldn’t even tell if the sub was on. 
 

As a note, I originally had my Ultra connected via Ethernet and assumed everything else (sub3 and eras 300) were connected via Sonosnet. But I’ve read that with the Ultra—if it’s Ethernet you will need the sub Ethernet connected. 
 

so after my resetting all products, I setup everything including the Ultra on WiFi only. Whether this or the mass reset was the fix (or both) I cannot say. 
 

I will also say that I never ran Trueplay after either attempt  

I have a sub mini and noticed what others have posted on this thread. Even with latest firmware, the arc ultra will keep emitting sound, as low as 45hz (tested with frequency generator). Adjusting the sub level seems to affect how much bass is emitted from the arc ultra vs the sub. So, if the sub is turned on, but set to -15, all the bass will come out from the ultra. This seems like a crossover bug to me? I can reproduce this with and without trueplay. This behavior causes bass to be too boomy or missing depending on sub location (never had this issue with beam gen2).

At first glance it sounds very reasonable to my ears.
Let's say that 100% bass is emitted when playing a movie and the 100% is distributed 40% to Ultra and 60% to Sub. (I have no idea what the distribution is, it's just a guess.)
So Ultra gets its 100% bass with the distribution of 40%

If you then choose to set Sub to -15, its 100% bass with a distribution of 60% will be at such a low volume that it cannot be heard. Ultra with a setting of 0 and thus its 100% of the distributed 40% will therefore output the 100% bass you hear but still with a distribution of 40%

You will never be able to achieve more than 100% bass, however the distribution can be influenced by adjusting +/- on the bass and thereby seeming as if you get more or less than the 100% and a different distribution, but the fact is that 100% bass is still distributed at 40/60.

maybe it's reasonable. But, typically a “sub level” slider just controls the sub gain, it shouldn't affect crossover frequencies or how the bass is distributed which is clearly the case here.

And, at least in this room, the fact that the soundbar and the subwoofer overlap around 40-50hz creates a big peak of bass output at that frequencies which is very hard to eliminate.

Maybe this is all “by design” but it's unlike any other bass management gear I've tried. It would be nice to hear from sonos if this behavior is actually intended.

Maybe it's because I'm one of the lucky ones, or maybe I can't hear 

Had Sub Gen2 connected to my Ultra and Era300 now Sub 4. Have never experienced the lack of bass, and I love bass 
Have performed TruePlay Tuning (Quick) on each Sub, currently my settings are: Loudness on, Ultra: Bass -1 and Treble +2, Sub is at 0.

To ground my observations a little more. Here's the frequency response I get with the sub on, level set to 0:

This is what I get with the sub off:

And this is what I get with the sub on, and level set at -15.

(These are just quick sweeps taken with my phone, so to be taken with a pinch of salt).

The response graph seems to match what I'm hearing, in that having the sub at -15 doesn't limit the bass output, it just reverts to “soundbar only” mode. That is, it seems to me that either the crossover is set super low (say 50h), or the arc ultra response is not affected by a sub being there.

Hi ​@Matclane et al

We now consider this issue to have been resolved. Please ensure your Sonos system is up-to-date, and if you still experience this issue, please get in touch with our technical support team to report as much.

I hope this helps.

I know that you said this is considered resolved, but I received my Gen 4 sub today and am experiencing this exact issue with my Arc.  

Hi ​@Bmyers25 

Sorry to hear that! I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.

Thank you for confirming the lack of base is a recognised problem. I have just received my Arc Ultra and connected to my existing Sub Gen 3 only to be massively disappointed with the level of base.

Having just spent £1,000 on the Arc Ultra I hope Sonos address this issue quickly.

DISAPPOINTED!!!

Sold all my old gear ( Arc, Sub Gen 3 and pair of One SL’s) to a friend. For the Arc Ultra, Era300’s and sub gen 4. Thought this would be a small upgrade WAS I TERRIBLY WRONG!!

DO NOT MAKE THIS MISTAKE!!

I keep getting up to go over to the sub to see if it’s actually working. I’ve placed everything where the original gear was, TruePlay on or off and it SUCKS!

Even my wife who could care less about this stuff was like, That sounds like $h!t.

I’m now at the mercy of SONOS hoping there is a software upgrade and we all know that could be months if not years away.

STRONGLY RECOMMEND YOU DON’T MAKE THIS SAME MISTAKE.

Glad I found this form I thought it was just me.