Sonos Amp and High level input from Subwooder?

If you are using high level, there should be nothing plugged into the Sub out jack on the Sonos Amp; doing that will strip the lower frequencies from the speaker terminals. And if nothing is plugged into that jack, nothing you do in the Sonos controller app to the Sub will make any difference.
What does REL recommend connecting their LFE jack to?

In order to avoid "hum", they recommended to connect the sub out to their LFE, and just put the LFE on the sub to 0. Apparently this helps ground the system. I was getting some hum before I did this, and now it's fine.

So no danger connecting both the LEF and high level with a ground to the speaker neg terminal on the amp right? Seems to be working fine, just want to avoid any shorts or issues.

So the Sonos app sub settings will only control whatever is connected to the sub out amp correct? It did seem to have some effect, even with lfe turned down to 0 and high level being used.

I tried to use the low level output on the sub to the sonos sub amp first, with a mono rca cable, but I would get very low bass - only lfe and high level gave me the right levels. Any idea as to why that is? Volume and crossovers were the same as is working on the high level

So no danger connecting both the LEF and high level with a ground to the speaker neg terminal on the amp right? Seems to be working fine, just want to avoid any shorts or issues.


I tried to use the low level output on the sub to the sonos sub amp first, with a mono rca cable, but I would get very low bass - only lfe and high level gave me the right levels. Any idea as to why that is? Volume and crossovers were the same as is working on the high level
The way the Sonos Amp is architected, anything plugged into its sub out will immediately strip out low frequencies from the speaker terminals on it, even if there is nothing connected at the other end. So using that socket is not to be done unless there IS a working Sub at the other end that will reproduce the stripped out frequencies. And even with nothing connected at the other end, the Sonos app will work on the connected Sub out jack on the Sonos Amp, but obviously nothing will be heard if there is nothing at the other end. But, as explained, the main speakers will be deprived of frequencies below 80hz, whether the other end is connected to a Sub which is left at zero, or there is nothing connected to the other end.

There is no danger in connecting a double pair of speaker wires at the Sonos amp speaker terminals - one set running to the main speakers and the other set to the high end inputs on the Sub. As to the ground connection to the speaker terminals on the amp, if you do exactly what REL has recommended, there should be no danger; with respect to what is happening at its speaker terminals, the Sonos Amp is like any other stereo amp.

I don't know why the low level connection from the Sonos Amp sub out jack to the low level connection on the REL does what it does. Maybe the user manual will tell you what needs to be done if that route is used.

So no danger connecting both the LEF and high level with a ground to the speaker neg terminal on the amp right? Seems to be working fine, just want to avoid any shorts or issues.


I tried to use the low level output on the sub to the sonos sub amp first, with a mono rca cable, but I would get very low bass - only lfe and high level gave me the right levels. Any idea as to why that is? Volume and crossovers were the same as is working on the high level
The way the Sonos Amp is architected, anything plugged into its sub out will immediately strip out low frequencies from the speaker terminals on it, even if there is nothing connected at the other end. So using that socket is not to be done unless there IS a working Sub at the other end that will reproduce the stripped out frequencies. And even with nothing connected at the other end, the Sonos app will work on the connected Sub out jack on the Sonos Amp, but obviously nothing will be heard if there is nothing at the other end. But, as explained, the main speakers will be deprived of frequencies below 80hz, whether the other end is connected to a Sub which is left at zero, or there is nothing connected to the other end.

There is no danger in connecting a double pair of speaker wires at the Sonos amp speaker terminals - one set running to the main speakers and the other set to the high end inputs on the Sub. As to the ground connection to the speaker terminals on the amp, if you do exactly what REL has recommended, there should be no danger; with respect to what is happening at its speaker terminals, the Sonos Amp is like any other stereo amp.

I don't know why the low level connection from the Sonos Amp sub out jack to the low level connection on the REL does what it does. Maybe the user manual will tell you what needs to be done if that route is used.

Only issue if I unplug the Sub out from amp to the LFE on the Rel, the Sub gets a hum/vibration when music is off,and connected via high level.

I looked up the user manual online and did not find any reference to such a connection there. Where are you seeing it? When High level is used, per the user manual I found, the only connection from REL to amp is to its speaker terminals via the red, yellow and black cables at the other end of the REL supplied cable that has the speakon plug for use at the Sub end.

Further to the above, what happens if you let the black wire float, unconnected? If the hum goes away, properly cover the end of the black wire with insulating tape, and rollup/tuck it away out of sight.

If THAT does not work, what might is plugging a shielded RCA cable into the .1 LFE jack not to the Sub out on the amp, but into either of the two RCA input jacks on the amp. Via the shielding this should allow for grounding of the Sub to the ground of the Amp. I have not tried this myself, but seems to be a REL suggestion for amps that do not have a metal cabinet to which such a grounding can be done.
All the foregoing just shows how neat the Sonos Sub is; bond it to the Amp wirelessly with the app, choose the crossover based on how low the main speakers can go, and you are good to go. No worrying about high level/low level and grounding. If the sound is as good as REL, if not better, this begs the obvious question.

If THAT does not work, what might is plugging a shielded RCA cable into the .1 LFE jack not to the Sub out on the amp, but into either of the two RCA input jacks on the amp. Via the shielding this should allow for grounding of the Sub to the ground of the Amp. I have not tried this myself, but seems to be a REL suggestion for amps that do not have a metal cabinet to which such a grounding can be done.
All the foregoing just shows how neat the Sonos Sub is; bond it to the Amp wirelessly with the app, choose the crossover based on how low the main speakers can go, and you are good to go. No worrying about high level/low level and grounding. If the sound is as good as REL, if not better, this begs the obvious question.

The only way I was able to get the hum to disappear while using the high level connection was:

Black ground to amp speaker negative
Rca cable from LFE on sub to the amp sub out


But this seems to make the sonos amp do the sub processing right? Can I by pass that by turning off the sub in the sonos options?


High level cable with no black ground or Rca connected gives me a very loud hum noise, I’ve tried it all ways and above was the only that worked

Also, low level input did not seem to work well, very weak bass when connected via Rca cable to the amp sub out. Why is that?

LFE sub out to amp sub in has proper volume and works, as does high level save for the hum. Why is low level not working?

The only way I was able to get the hum to disappear while using the high level connection was:

Black ground to amp speaker negative
Rca cable from LFE on sub to the amp sub out

This exactly what REL says you should not do, as far as the first part is concerned, where class D amps are concerned, and Sonos Amp is from that class.
As to the RCA cable from LFE to the Amp, REL says that a RCA cable can be connected to any RCA jack on the Amp that is free, it need not be the Sub jack only. Grounding is done via the shielding on the RCA cable so plugging the RCA cable to the line in jack on the Amp should also work.
Above two points as per REL videos on how to connect their Sub to an amp. If this is not working for you, I suggest you ask REL for help and return the Sub if they cannot solve the problem, subject to the next paragraph:
Plugging anything, even a blank plug into the Sub out signals the Sonos Amp to strip out the lower frequencies from the Amp speaker terminals. You cannot bypass that - all that turning the Sub off in the Sonos options does is turn off the Sub; this is a new feature and I suspect it does not restore the full frequencies to the speaker terminals. But there is no harm in trying this and seeing if it changes the overall sound quality in a beneficial way. I believe it will not make any difference, but I could be wrong, because I do not have this feature on my Connect Amps.
I don't know why low level isn't working; another question for REL, that.

The only way I was able to get the hum to disappear while using the high level connection was:

Black ground to amp speaker negative
Rca cable from LFE on sub to the amp sub out

This exactly what REL says you should not do, as far as the first part is concerned, where class D amps are concerned, and Sonos Amp is from that class.
As to the RCA cable from LFE to the Amp, REL says that a RCA cable can be connected to any RCA jack on the Amp that is free, it need not be the Sub jack only. Grounding is done via the shielding on the RCA cable so plugging the RCA cable to the line in jack on the Amp should also work.
Above two points as per REL videos on how to connect their Sub to an amp. If this is not working for you, I suggest you ask REL for help and return the Sub if they cannot solve the problem, subject to the next paragraph:
Plugging anything, even a blank plug into the Sub out signals the Sonos Amp to strip out the lower frequencies from the Amp speaker terminals. You cannot bypass that - all that turning the Sub off in the Sonos options does is turn off the Sub; this is a new feature and I suspect it does not restore the full frequencies to the speaker terminals. But there is no harm in trying this and seeing if it changes the overall sound quality in a beneficial way. I believe it will not make any difference, but I could be wrong, because I do not have this feature on my Connect Amps.
I don't know why low level isn't working; another question for REL, that.

First, thank you for the detailed answers, I appreciate it.

I did also contact Rel and Sonos, Rel will get back to me after talking with an engineer. Seems like not many people have the new Sonos Amp and a Rel sub and have done this, or at least have not asked about it to them or online much.


To answer your question, using high level input I and lfe at the same time (They recommend having both, for movies and music i guess) and if I turn off “sub” in the Sonos app, I do get a difference in sound. Control seems to be reverted back to the sub, I can adjust the crossover and volume on the sub itself and it seems to be working. When I turn sub back on, it seems to add some sort of digital processing that changes the nature of the front speakers sounds.

The hum I am getting is audible if I turn the crossover up high, and when the sound is idle after playing. It auto standby after a few minutes and the humming seems to stop. The ground on or off, same result. RCA cable to lfe or Rca out, same result with high level. If I remove the Rca all together, I get extremely loud humming on the sub at all times.


I do have a Sonos Sub as well, but that’s paired with my 5.1 system and I do like the sound of this Rel for music, as that is what I use it exclusively for.

It might be useful to open a thread here on the following question:

What happens at the speaker terminals of the Sonos Amp if a blank jack is plugged into the Sub out jack? Are the speaker terminals then denied frequencies below the crossover setting of 80Hz even if there is nothing at the other end of the jack? And then does turning the Sub on/off in room settings for the Sonos amp in the Sonos app have any impact on what happens at the speaker terminals? Are low frequencies restored to the speaker terminals with the jack plugged in, but the Sub setting on off?

And/or pose this question in an email to Sonos Support.

All other questions are for REL to answer. But if you like the sound from the REL sub compared to the Sonos Sub, I would just keep listening to it and not overthink the matter.