The Sonos ecosystem is constantly growing and, with the new Sub Mini, appealing to those operating in smaller spaces. Stephen Dawson takes the new sub for a test drive.

Two years ago, we took a deep dive into a full Sonos surround system, with a Sonos Arc soundbar at the front, two Sonos One speakers for surround, and the Sonos Sub for bass. The Sub proved to be remarkably competent, delivering strong, deep bass (I measured an impressive 27 to 92 Hz ±3dB).

But that unit would clearly be overkill for a Sonos system based on one of the smaller soundbars, such as the new Sonos Ray or a pair of Sonos One SL speakers.

Which brings us to the newest entry into the Sonos stable, the Sonos Sub Mini wireless subwoofer.

What it is

Well, obviously, this is a subwoofer. It is purpose-built for working with Sonos speakers, and only Sonos speakers. There are no audio inputs – digital or analogue – only network connections. And the only protocols it will understand are those managed by the Sonos app. Sonos says that it is compatible with all current Sonos wireless speakers, plus several of the older ones: Play:1, Play:3, Play:5 (Gen 2), One (Gen 1 or 2), One SL, Five, Arc, Arc SL, Beam (Gen 1 or 2), Playbar, Playbase and Ray. And also the IKEA SYMFONISK range.

It is only compatible with the S2 version of the Sonos app, introduced in August 2020, so if you’re using Sonos speakers running the older software, you’ll need to update them for them to work with the Sub Mini.

Both WiFi (802.11a/b/g/n dual band) and Ethernet (10/100) are supported. And, of course, you can use it for such things as sound from your TV, but you will have to plug the optical output from your TV into the soundbar or speaker (HDMI will also work for the Arc), and that will then feed audio to the Sub Mini via the network.

At first glance, the Sub Mini is quite similar to the larger Sub, apart from one glaring difference: it is round, while the Sub is square. Specifically, it is a cylinder, standing 305mm tall and with a 230mm diameter. There are two vertical 50mm-wide slots, one on each side, from which the sound emerges.

Peering into them, you can see on each of the two internal faces a 152mm (six-inch) woofer. These operate to kind of squeeze the sound out through the slots, and because they mechanically oppose each other, no matter how furiously they vibrate they won’t shake the subwoofer around on the floor. It, I should note, weighs a little more than six kilograms, compared to the 16kg of the larger Sub.

There are also several major differences which are less visible. While the Sub uses a bass reflex design, with the ports venting into the same internal space as the drivers, the Sub Mini is a sealed design, also known as acoustic suspension. That enclosure design, left to itself, tends to roll off the bass at a higher frequency, but less steeply. Sonos has included digital signal processing that adjusts the frequency balance for this effect. That would require harder work from the amplifiers. Sonos doesn’t publish power output figures, so we just have to rely on how things sound to see whether sufficient power is provided for this purpose.

Another difference is that only one Sub Mini can be used in a room, while you can link two of the larger ones into a single room system. I guess that makes sense. If you want more bass, just go with the larger model. But I wonder why a feature already provided within the Sonos system isn’t available for this model.

Anyway, Sonos says that the Sub Mini “works best … in a smaller room and at low to moderate volume levels. If you have a larger space or intend to listen at higher volume levels, Sub will provide a better experience.”

The Sub Mini is available in white or black. I reviewed the black model. Unlike the Sonos Sub, which is finished in a piano gloss, the black Sub Mini sports a matt finish, which tends to match most of Sonos’ speakers.

Setup

I expect most people will use WiFi rather than Ethernet connections, so I decided to go that way for the test setup. Westan sent me a Sonos Ray soundbar to go with the Sub Mini.

I put the Ray under my TV and connected them via optical cable and powered up both the Ray and the Sub Mini.  Its ethernet and power connections are nicely out-of-sight on its underside. Both devices display a slowly flashing light when powered up. I already had the Sonos app running on an iPad, and within a few moments it had popped up a picture of the Sub Mini and invited me to “Add” it. I tapped the button and after another moment, it told me that I needed to enter an 8-digit PIN printed on the bottom of the Sub Mini.

“Can you see it?” it asked.

This was new to me. I’ve been using Sonos gear for a few years and I don’t recall this requirement. I agonised a little. Should I run through this setup based on optimal circumstances (i.e. I knew I’d need the PIN), or worst-case conditions? While I was tempted to go optimal, I noticed that the minimalist three-step “Set Up” card included with the Sub Mini said nothing about serial numbers. It said, 1: place your products, 2: plug it into the power, 3: hit “Add Product” in the app.

My review philosophy is to act as a person new to the technology in question. So had I followed the setup card, I would have got to this point, perhaps having placed the Sub Mini in an inconveniently inaccessible place before realising I needed to note the PIN.

So I answered “No” to the question “Can you see it?”, thinking there might be a workaround. But the app informed me that the PIN was essential and hitting “Continue” took me back to the previous question. So I went over, tipped the unit upside down, and entered the number into the app. Then you have to hit the connection button on the unit. Only a few seconds elapsed before connection was complete and, as is the way of these things, the app told me that the update available for the unit “must be completed … before you can use it.” I was wondering what to do to occupy my time while the update was happening, but before I decided, it had completed.

The app then wanted me to connect the Sub Mini with an existing Sonos speaker or soundbar. It turned out that the Sonos Ray with which I was reviewing the Mini was not in factory condition – I’m guessing it was a review model which not been reset – so I cancelled out of that connection. A quick factory reset of the Ray had it going within a couple of minutes, then back to the app and I could link the Sub with the Ray.

And that was it. The system was ready to go.

Apart from that PIN oversight, I have to compliment Sonos. Over quite a few years I’ve installed many wireless audio systems, and few have gone as smoothly and reliably as this one.

The final step is optional: using the Sonos “Trueplay” function to tune up the system for the smoothest response in your room. This is a routine within the iOS version of the Sonos app. If you don’t have an iPhone or iPad, you could consider asking a friend with one to connect to your network, install the app and then run the routine. You’ll only need to do it once.

In use

As suggested above, there are two ways of feeding audio to the system to which the Sonos Sub Mini is connected. One is via the network, and one is via a digital input into the (in this case) Ray soundbar. The Sonos app allows you to connect various streaming services to which you’re subscribed. I used Spotify. You can also feed music via DLNA. The Sonos app is fussy about the DLNA servers it supports as a DLNA controller, and it has never worked with Media Server in my Synology NAS, but you can use other DLNA controller software (such as Bubble UPnP, which I use on Android) to send music to the Sonos system.

Or you can select the digital input (optical in the case of the Ray). A setting in the app has the system switch automatically to this input when a signal is detected. It worked exactly as it was supposed to. When I switched on the TV, the network audio stopped playing and the TV’s sound emerged.

As part of the setup, you’re given the chance to have the Ray learn the remote codes for the volume control on your TV’s remote. (More accurately, it uses the volume up code from your remote to identify your TV model and then it also accepts the volume down and mute codes.) You can also control the level with a volume slider in the app.

Whether you’re feeding audio via the network or from the TV, you have a lot of control over the sound via the app. You can switch the subwoofer on and off, for example, or set its relative level to the other speakers. Sonos has the system defaulting to what it thinks is the best balance between devices. You can also adjust the bass and treble.

So, how did the subwoofer sound? Really quite impressive. Kick drums were very solid, and I felt like there was nothing missing at all in the deep bass on music. For example, the No, Virginia album by the Dresden Dolls left nothing missing at the bass end. The treble and midrange (delivered by the soundbar) was reasonably competent – given the pricing the Sonos Ray, it was actually quite impressive – but the Sub Mini carried the kick drums and bass guitar extremely well. Within limits, though. With modestly room-filling levels all was great. Too loud and the subwoofer’s controls limited its level a little. That’s fine. Self-protection is a proper design goal. If you want to blast extremely high levels of bass from your Sonos system, get a Sonos Sub, or two.

With some material – such as Ghost in the Machine by The Police – there did seem to be a gap in the bass output. The deep stuff was definitely there, but the upper bass was sometimes a little recessed.

Almost needless to say, the whole system was enormously better than the sound of my TV. With the solid bass underpinning from the Sub Mini, action shows on TV were lent a previously absent authority.

Subwoofer extension

Sonos says that the Frequency response of Sub Mini is “as low as 25 Hz”, which isn’t very instructive, really. A quick measurement with the microphone up close to one of the slots showed that the Sub Mini was outputting from 26.6 Hz to 80 Hz ±3dB. At the high end, it looks like Sonos applies an 18dB/octave low pass filter above around 90 Hz. The output was 6dB down from the average at 25 and 95 Hz. By 20 Hz the output was at -18dB. At the bottom end those figures look slightly better than those of the larger Sub, but the main difference is going to be output levels, not extension.

One question that I wondered about was whether the Sonos system uses the presence of a subwoofer to relieve part of the load on the soundbar. That is, does Sonos stop the soundbar from trying to reproduce bass when the subwoofer is running? To check that I left the subwoofer powered up and connected, but put it out of the way. And then I measured the bass output of the Ray with the microphone up close to it. With the subwoofer disabled in the app, the bass output of the Ray was maintained at full level down to 56 Hz, at which point it was cut off hard.

With the subwoofer switched on, the bass output from the Ray was reduced, with a 6dB per octave high pass filter cutting in at 140 Hz. So the Sub Mini not only adds deeper bass, it frees up capacity for the Ray to devote to the midrange sound.

Conclusion

You may be wondering about why I’ve kept mentioning the Sonos Sub within this review of the Sonos Sub Mini. Well, if you have Sonos speakers or a soundbar, you have two options for enhancing their bass. There are no third-party solutions. And neither Sonos Sub, large or small, will work with any other system.

So, consider this review a guide more towards which of them suits your requirements. If the $400 difference isn’t important, go for the bigger one. But for many, many systems that’s overkill. And in those cases, the Sonos Sub Mini will do the job extremely well.