Two speakers playing the same track a quarter of a second apart sound worse than one speaker playing it alone. That delay is the entire problem, and it is why multi-room audio products exist at all.
There are three ways out of it, and only one of them is a purchase.
One amplifier, several pairs of speakers. There is no synchronisation problem, because there is one source. A stereo amplifier with an A/B switch, or a multi-zone amplifier, feeding speaker cable to each room. Cheapest per room, best sound per pound, and the volume in each room is set at the wall or the amplifier rather than from an app.
Several small computers, kept in step in software. A Raspberry Pi or a mini PC per room, each with its own speaker, all told to start the same audio at the same moment. This is what Multilarm's Rooms feature does, and what Snapcast and similar projects do.
A commercial multi-room system. Sonos and its competitors. Buy speakers, open an app, and it works.
Well enough for announcements and background music, and honestly stated rather than implied: Multilarm's room synchronisation was measured on real Raspberry Pi hardware over ordinary wired and wireless networks, and the figures — with the method used to obtain them — are published on the measured data page rather than described in adjectives.
The practical test is not a number, it is a corridor. Stand in a doorway between two rooms. If you hear one performance, it works. If you hear a flam or an echo, it does not. Wired Ethernet passes that test comfortably; congested Wi-Fi is where any software approach, including the commercial ones, gets harder.
Sonos wins on four things, and leaving them out of a page like this would be dishonest. It sells well-engineered speakers with their own amplification and tuning; it sets up in minutes with no networking knowledge; it has properly licensed streaming-service integration; and its app is polished. Multilarm is software, and the sound is whatever you plug it into:
If those are the things you want, buy Sonos. It is a good product and this page is not going to pretend otherwise.
The software approach wins on cost per room, on breadth, and on outliving its vendor. Once more than about three rooms are involved the price difference stops being marginal, and the same system that plays background music also announces, schedules, speaks typed text, ducks the music and drives a relay. In detail:
For a room that already has a powered speaker or an amplifier input: nothing but a small computer and a cable. For a room with nothing: a powered speaker. That is genuinely the list.
Can Multilarm play Spotify or Apple Music?
No. It plays local files — MP3, WAV, FLAC and OGG — and internet radio streams. Streaming services require licensed integrations, and a product that claimed one without having it would be lying to you.
How many rooms can it keep in step?
Rooms is designed for the scale of a house, a mosque or a school block rather than a stadium. The limit in practice is your network, not a licence count.
Do all the rooms need identical hardware?
No. A mixture of PCs and Raspberry Pis is fine, and different speakers per room are expected.
Can one room play something different?
Yes. Rooms can be grouped or addressed individually, so the kitchen can carry an announcement while the workshop keeps playing music.
Is there a subscription?
No. Personal, non-commercial use is free permanently, and institutional use is a one-off perpetual licence. The only optional recurring cost is remote control from outside the building, which multi-room music does not require.