Or will I have to go to Sony or Sennheiser for a soundbar that has wifi and bluetooth support? 

For a room of this scale I think that you should use a full home cinema system, not a soundbar.

Thanks. But I use it as a dance floor and photography studio as well. So I can’t have permanent speakers. I need a solution that I can just take out of a cupboard and put underneath the 7 meter screen/wall and have Dolby Atmos or DTS Surround immediately, plug and play when I want to organise a movie night. Then store away the speaker when I’m done.

This is why I’m interested in a single speaker (sound bar) solution.

I’m not an audiophile so I don’t need the best of the best 3D (I’ve used a largish mono bluetooth speaker for that screen until now FFS )

I’m just concerned at:

1. the size of the room (15 foot high ceiling)

2. the placement of the speaker 20ft away by cable from the source of the sound input (PC)
3. the lack of wireless capability in Sonos products
4. whether a 20 foot S/PDIF cable is going to cut it in delivering 3D sound for blurays.

I wonder if Sonos Arc is the correct product or if I should go for a wireless soundbar like the Sony HT A7000 or just wait until Sonos releases a wireless Arc?

The Arc ideally requires an eARC HDMI connection from a TV source.  Your set-up is not something that the Arc was specifically designed for but it is possible with a product similar to an Arcana HDFury. This device will split the Audio to the Arc and the Video to the Projector.  Assuming that your source will output either a Dolby Atmos or DTS signal.

I’m a bit confused on one hand you say that you’re not a audiophile but then state specific audio formats…

FYI - I’m not sure that BT will support those formats, so the Arc will be best via the HDMI cable.

Thank you. I do not use TV sources. This is a home cinema so it is primarily 2D and 3D blurays.

1. What is the difference between using eARC HDMI connection to the Sonos ARC (which will require an additional $250 Arcana HD Fury purchase) and the Sonos ARC built in S/PDIF cable.

2. I am not an audiophile as I do not know the technical details. For example I am not even sure an HDMI 1.4a cable or an S/PDIF cable can surround sound output like Dolby Atmos or DTS. I just assume they do. I mentioned the Dolby Atmos and DTS Surround format as these are the formats that Blurays supply surround sound output in. The PC I run can decode any 3D format (like Dolby Atmos) for free using Hesuvi.
3. I am not sure about your BT statement. In all the shops where I live they say the Sonos Arc’s is great, and it’s only downside is that it has no wireless/bluetooth capability compared to the competition like Sony HT A7000, Sennheiser Ambeo,  Bose Smart 300 or the Harman Cardon Citation. All of these competitors have Bluetooth functionality and surround sound support. I am therefore assuming that Atmos support through wireless should be possible.

Can you get Atmos from optical, which is the output you say the pc provides? I’m sure someone can confirm, but I thought it would need HDMI connectivity. 
 

How big is the room, if it’s also a dance studio? Will a soundbar output at high enough volume to fill the space? 

You’ll need an HDMI-eARC connection to SONOS ARC for Atmos.

Again, I don’t think that a soundbar is the right approach for this space.

https://www.digitaltrends.com/home-theater/how-to-buy-a-soundbar/
 

States that optical (S/PDIF) is not capable of delivering Atmos. Only ARC is capable of delivering Atmos. eARC is needed to deliver DTS-HD and True HD beyond that.

The question remains whether these other brands have achieved eARC transmission capability over wireless.

You are right about eARC. I am unsure if that requisite stands in the “wireless” soundbar arena.

Why do you think a soundbar is not the right solution? Is it because the Sonos Arc upward firing speakers will have trouble with a high ceiling (15ft in this case) to get the sound to reflect back behind the viewer?

I don’t know if there is a specification Sonos has published on room dimension limitations but it would help in this case.

Personally I prefer the soundbar solution as it is a single device I could just place and remove as needed when watching a movie. If it gives a semblance of Atmos it would be enough for me. (I’m more concerned about surround sound quality than outright volume, as I do have neighbours to contend with).

You seem reluctant to accept the advice being given. Sonos do offer a “home trial” in many regions, so you could take advantage of that and try it out for yourself. Perhaps you could report back on how it works out for you?

I would happily and gratefully accept the advice given if there had been a specific example of why  a soundbar would not be the best solution.

I made the assumption myself that a 15ft ceiling height might prove too much for the upwards firing speakers in a soundbar. I also stated that outright volume is not a prerequisite if the argument was that a similarly sized room might be too large for the overall sound output of a soundbar.

In any case, using Sonos Arc as a solution appears moot in my case as I realised the PC GPU I use uses HDMI 2.0b (GTX 1080Ti). This is not enough for eARC. eARC needs the HDMI 2.1 specification. 
 

It looks like I am forced to look for a wireless solution.

What everyone is trying to say is that a single device for a large space may be pushing the capabilities of any device, however that is connected.  The ceiling height is irrelevant unless you are going to use Dolby Atmos, it is the sheer size of the room that is of concern.

I appreciate the advice, I really do. Thank you for having taken the time to offer suggestions. I’m glad people have been so helpful.

I thought I’d be satisfied by any of the products we’ve discussed as I have been happily using this for sound under that 300inch screen in the space in question for the past 8 years. 
 

I thought anything would have been better than that.

In any case, I will continue the hunt. Should I find something that works amazingly well I will add to this post in the future should it help others.

I think people would be able to give you much better advice if you gave actual dimensions of the room.  The screen size isn’t really relevant to audio, and the 20 ft cable length doesn’t really tell you anything either.  You can make assumptions, but nothing really reliable.

It does not sound like an Arc soundbar is the right solution for you...I agree with the others.   15 ft ceilings do not lead themselves well to atmos audio, at least if you are going to use upfiring speakers like with the Arc.  I would guess that you aren’t going to get much from the side firing speakers either.   And Sonos speakers are not designed to be stored away when not in use.  They are meant to be always on.  And you only mention TV/projector audio, no mention of streaming music or multiroom audio.  Essentially, you are spending a lot for features you aren’t interested in.

Honestly, I’d say the same with any of other high end soundbars.  It’s the wrong tool for the job.  You are going to need to run a wire between the PC/projectors.  I get the appeal of a soundbar, but you if you are looking for something that’s quick to setup for a large space, I think you’re better off with a amp + pair of speakers or 2 amplified speakers for stereo.  You can’t really do temporary surround sound well, you’ll be better off with good stereo.

Regardless of your approach, you’ll need an HDMI-eARC connection between your video source and the sound system if you want access to premium audio formats. So far I’ve seen only one device that claims to offer wireless HDMI-ARC. I have no experience with this device. With any wireless HDMI device expect some pain. There is ongoing technology development. A couple years ago I’d say “no way” for wireless HDMI. Now it’s “maybe”. I expect that, as WiFi7 rolls out, wireless HDMI will become more practical -- but this is pure speculation on my part.