I don’t know of any projectors that do any version of ARC, either HDMI-ARC, or eARC. 

So, I concur with your second thought, although I’m not familiar enough with that specific TV set to know its capabilities. 

That LG C9 supports Atmos via TrueHD via eArc.  

https://www.rtings.com/tv/reviews/lg/c9-oled

That’s all you would need for Atmos all the way up to Atmos via TrueHD sources.  Note: Atmos via TrueHD is is only available via 4k Blue-Ray.  Streaming sources, if they have Atmos, send it via DD+.

@jgatie Does that mean that streaming devices, like a newer Apple TV, connected to the LG C9 would not be Atmos compatible with the Sonos Arc?

Not sure.  The latest Apple TV 4K does have Atmos support.  The Arc will decode Atmos with TrueHD, DD+, and Dolby MAT.  There seems to be some confusion as to whether Apple TV 4K does these codecs or converts to multi-channel PCM.  I’d check with Apple.  

We've had some discussion in the Arc announcement thread about using it with a projector. The problem is connecting it.

As @Airgetlam pointed out, there are precious few projectors that do ARC. None that I know of do eARC.

There are a few main reasons.

1) people who own projectors tend to use AVRs with dedicated HDMI In/Out, since it is more a space for enthusiasts who would frown at an Atmos soundbar. 

2) In addition, projectors do not have internal tuners or apps that output audio, so another reason they don't need ARC.

3) More generally projectors were never designed to be HDMI hubs like TVs are. They were never intended to handle a lot of different inputs, or route or transcode audio.

4) projectors are currently limited to 4K. There is just no need for the bandwidth of HDMI 2.1 that also brings eARC.

So for now, your best bet is to go with a TV that neatly passes through everything on ARC or eARC.

I’m in same boat with a projector. Is there a AV receiver or HDMI splitter that would work to pass the ARC audio in a setup with ATV 4K?

I have projector, Sonos base and a HDMI spitter which split the video to projector and the audio to playbase via coaxial cable. Is there any such HDMI splitter available to pass through DD+ or Atmos via HDMI arc ?

In the end I’ve gambled somewhat on the HDfury Vertex2 which allows splitting from one source to two outputs, each with separate EDIDs negotiated on the link, and with explicit support for eARC and de-embedding Atmos.

I’ve got a JVC DLA-NX and the following pushed me over the edge into committing to the gamble:

used by JVC projector owners to apply their own gamma curves for HDR content and allow their projector's dynamic iris to work with HDR content

https://www.avforums.com/reviews/hdfury-vertex-review.15094

I’ll try and track down the conversation mentioned by @Sjoop1985 and see if this was a proposed approach.

Last night I contacted HDfury about the vertex2 to see if it would allow me to send an AppleTV signal to an Epson 5050ub projector while At the same time sending Dolby Atmos from the Apple TV to the Sonos arc…

their tech support said:  

No there is no solution in the world for Sonos currently, we will have one by the end of the year.

would an hdmi switcher like this not work?  Not sure of the price and may not be worth it as I know these can be pricey.  But it says it splits hdmi audio and video and “supports audio pass-through up to dolby ATMOS”.   

https://muxlab.com/pro-digital/6x1-2-0-multimedia-presentation-switch 

Nope. Passthrough just means it can forward audio on the normal audio channel. ARC isn't even mentioned, and that is what is needed.

We need a switch that can do what a TV does - take the incoming audio channel on one HDMI-IN, and return it over ARC on another HDMI-IN, to which the Arc is connected. So far, there is no such thing.

Lovely.  I just got notice that my ARC has shipped.  Doesn't look like I’m going to get the upgrade over the playbar, I’m currently using, that I was hoping for.  

Would something like this not work? It’s not technically splitting the audio from the video signal, but if you sent the regular hdmi out to the projector and the ARC hdmi out to the soundbar would that not work to get an atmos audio signal to the soundbar and an image to the projector?

https://www.amazon.com/NEWCARE-HDMI-Matrix-Switch-Splitter/dp/B07ZNKF7C8/ref=sr_1_11?dchild=1&keywords=hdmi%2Baudio%2Bvideo%2Bsplitter%2Barc%2Bdolby%2Batmos&qid=1591905756&s=electronics&sr=1-11&th=1

It doesn’t create the ARC Or eARC signal, it just passes the one created by the TV. 

I’ll take a look at it.  By way of an update - new ARC speaker arrived yesterday and I can’t get it to work even using the hdmi to TOSLINK (optical) adapter they include in the box.  Makes no sense.  My prior setup was an HDMI in, to an optical and hdmi out splitter (hdmi going to projector and optical to playbar).  Not sure why it wont work now when all I did was add the adapter to the optical out.  Frustrating!

newbie here but been looking to hook up 4k ultra short throw projector with the new Sonos ARC to achieve atmos.  Projectors like the Vava 4k (https://www.vava.com/products/4k-ultra-short-throw-laser-projector-1) and Optoma P1 (https://www.optoma.co.uk/product-details/uhz65ust) have eARC HDMI connections. 

Would these not allow for Atmos pass through say from an Apple TV 4k box > into the projector > and then into the Sonos ARC?  I’ve seen the Vava website says it doesn’t support ATMOS but it’s not clear if that refers to the native built-in HK soundbar vs passthrough via eARC…

I have both a LG OLED TV and the LG HU80ka Projector and have been doing tests over the weekend.

The TV is amazing. Everything worked on Atmos, the sound is amazing and you are able to watch it with light during the day.

The Projector is were I enjoy the movies the most. 120”, and very good quiality if there is no light in the room. Regarding Atmos, from the FireStick I get Atmos on DIsney Plus, Tidal and Prime. Not on Netflix or AppleTV. There are 2 possible workarounds for Netfix. Buying the Cube form Amazon or installing Kodi and the add-on on the Fire Stick. The AppleTv does not detect immersive sound so all I can get from it is 5.1

Hope this helps.

Glad I found this thread - was just about to click buy on an Arc.  From what I’ve read above I can’t get Atmos - is this correct?

Current set up is:

Devices into a 4x2 Matrix.

Matrix HDMI 1 out to 4k projector.

Optical out to Sonos Playbar.

The matrix has a second HDMI out so I thought I’d be able to pump that into the Arc HDMI, but from what I now understand this won’t work as it doesn’t carry eARC.

Is this correct?  Thanks

Regarding the HDMI,Is it regular ARC or no ARC at all?

HDMI switches don’t currently create either ARC or eARC signals. They do split off an optical signal from an HDMI input. But that is maxed out at Dolby Digital (5.1) due to bandwidth on optical. 

There is a device being worked on to create eARC signals, being discussed here, but it isn’t to market yet. 

Any HDMI switch with an optical output must be fed a Dolby Digital signal to work with Sonos. They can’t transcode a DTS, Dolby Digital Plus, or Atmos signal. 

Thank you.  Guess I’ll be waiting for a solution or sticking with Playbar and 5.1.

Understand where you’re coming from. My Vizio won’t pass Dolby Digital Plus either, but even with regular old Dolby Digital, I’ve found the Arc to be an upgrade from the PLAYBAR. I’m waiting on the new device too, but enjoying the Arc in the meantime. 

Glad i found this thread. I was also hoping to go for atmos in my setup with projector and Arc but doesn’t look possible yet. Thanks for info.

Hold off Just for now.

Its the 17th of June 2020 and I purchased an arc last week and it is so far no go.

The Arc may not work with a projector

My config is this

A Yamaha receiver. A Sonos Arc. A Epson HD projector

Before last week I had a Yamaha receiver with surround sonud passive speakers powered by the Yamaha, and the Epson projector. all has worked fine for years

The problem

We cannot get any signal from the receiver to be recognised by the Arc.

First try

The Yamaha has a single HDMI ARC output, so I used a 18GBPS splitter to send 1 signal to the projector and one to the arc. The projector works on either of the splitter outputs, but the arc does not recognise any signal from any output. during the sonos arc setup its says “no signal found”

Second try

The dealer I purchased the sonos arc from gave me a new $6000 Dual HDMI Output receiver to try. I took it home and no luck. Again the projector works in either HDMI output, but the sonos arc says “no signal during the setup. The receiver has eArc outputs

What does work?

I can successfully complete the wireless setup and get music through the sonos arc. but thats it. In the last week I have gone through the factory reset process about 20 times but no luck

What next?

I have returned the sonos arc to the dealer and they are working on it. A senior onsite engineer was there and said that it probably wont work, as the TV pass thru senario is different than the splitter or 2 hdmi output senario and new HDMI protocols are really tricky

I’ll keep you posted

My guess is the Sonos Arc will get a firmware update later down the track, but don’t expect the projector and Sonos Arc to work right now

The Sonos Arc isn’t what needs an update. It works fine. It is looking for an HDMI ARC signal, unless you’re using the optical cable connected to the adapter that the Arc comes with. You can’t feed a normal HDMI signal to the Arc using any splitter, as that would be just the normal HDMI signal, not the HDMI ARC signal the Arc is looking for.