PSB M4U TWM review: zero frills, stunning sound

Wireless earbuds now come with so much built-in technology it can be easy to forget the most important question: How do they sound?

And if you follow that line of thinking, the next question might be this: what would happen if a company focused all of its efforts on creating the best-sounding earbuds and ignored literally everything else?

Well, wonder no more. The M4U TWM from Canadian audio company PSB Speakers are — for better or worse — the most bare-bones wireless earbuds I have reviewed. Despite their $200 price, the list of features they lack compared to similarly priced earbuds is so long it’s almost comical.

Noise cancellation, transparency mode, side-tone for calls, wireless charging, wear sensors, head tracking spatial audio, a product locator, control customization, and LE Audio/Auracast compatibility — they’re all no-shows on the M4U TWM.

They’re essentially wireless in-ear monitors (IEMs), meaning there’s almost no reason to buy them if they fail to impress on sound quality.

I won’t keep you in suspense. The PSB M4U TWM sound fabulous.

Barebones buds

It’s hard to overstate how understated the M4U TWM are. I’ve seen $40 earbuds from Amazon that come in fancier packaging.  You get the earbuds in their case, two extra sizes of silicone eartips, a short USB-A to USB-C charging cable, and a quick-start guide that overlooks two very important features (more on that in a moment).

The charging case has soft, rounded corners, and the hinge works well. But the plastic itself has a cheap feel, and as I indicated in the intro, the case lacks wireless charging.  If PSB is trying to convince buyers that their $200 is being spent purely on sound quality, it’s done a helluva job.

A four-LED indicator on the front shows the case’s battery level. They light up whenever you open the case, or you can use the small button below at any other time to check the charge.

Buttons on charging cases are usually for putting the earbuds in pairing mode, but not on the M4U TWM. This one is strictly for the battery status.

The earbuds are a bit on the bulky side — they stick out a fair bit once they’re in your ears — but they’re very light, and I found their shape to be very comfortable. I had no problem getting a good fit and seal with the default eartips, but I worry that three sizes may not be versatile enough, especially for those with smaller ears.

I’m surprised that PSB declined to provide more sizes and shapes. A good seal is absolutely vital to getting the best sound quality, so you’d think that PSB wouldn’t want to leave that to chance over the few extra cents it would have cost to provide more eartips.

I ended up switching to the larger tips, and you may want to do the same. I found it gave me better noise isolation, a more secure fit when jogging, and better bass response.

Big ol’ buttons

If you’ve read my previous wireless earbud reviews, you know I’m a fan of physical buttons. Their tactile nature means you can operate them even with gloved hands, and the mechanical click they provide leaves no doubt as to whether you’ve pressed them accurately or not.

The M4U TWM’s buttons fall squarely into this camp, and they’re a pleasure to use. The button takes up the entire flat outer surface of each bud, making them impossible to miss.

There’s no way to customize their gestures, and yet, with so few actual functions, it’s easy to remember how they work. You can control play/pause, track skipping (forward/backward), volume up/down, voice assistant access, and call answer/end. That’s it. The quick-start guide neglects to mention the voice assistant, so here’s a tip: it’s a long-press on either earbud.

As good as these buttons are, I’m slightly freaked out by their construction. The teardrop-shaped surface appears to be connected via a pivot mount, which allows the edges to lift slightly when you press the opposite side. It creates a gap large enough to admit a pin or a small knife blade.

Not that I think most people will go poking sharp objects into these earbuds, but I could see debris collecting under the surface where it could eventually cause problems.

Still, I may be overreacting. PSB claims the M4U TWM are IP65 rated, which makes them effectively dustproof and water resistant enough for some serious workouts.

Two devices are better than one

Bluetooth Multipoint is rapidly becoming the norm in wireless earbuds, and I couldn’t be happier about that. The M4U TWM supports this handy feature, but you’d never know it by reading the quick-start guide or even reading the product specs.

After reaching out to PSB Speakers to ask why it wasn’t included, I can now tell you how it works: just unpair the earbuds from the first device, and they’ll automatically re-enter pairing mode so you can pair your second device. Easy.

Just don’t forget to put the buds back in their case and close the lid for a few seconds; otherwise, the controls may not work correctly. Once you pull them back out, you can seamlessly switch between paired devices — even if one is an iPhone and the other is an Android.

Stunning sound

Inside the M4U TWM is dual driver architecture that combines a planar magnetic transducer with a dynamic transducer, which has never before been tried in a set of wireless earbuds.

Planar magnetic drivers have become audiophile favorites over the years because of their lightning-fast responsiveness and vanishingly low levels of distortion. However, in my experience, when planars are used exclusively in a set of IEMs (like the Audeze Euclid or Campfire Audio Supermoon), the low end can sometimes lack authority.

I suspect PSB feels the same way, which is why it chose its hybrid architecture for the M4U TWM. The planar driver delivers the highest frequencies, while the more traditional dynamic driver handles the lows. In case you’re wondering, PSB says the crossover is set around 2,000 Hz.

The result is impressive. The M4U TWM deliver among clearest details I’ve ever heard from a set of wireless earbuds without sacrificing any low-end bass response.

I knew PSB had something special the moment I started listening, and it was confirmed as I began swapping them with the other flagship earbuds in my collection.

One of my favorite tracks for testing soundstage precision is Yosi Horikawa’s Bubbles. The intro is the sound of a series of beads and balls being dropped onto hard surfaces. With most earbuds you can close your eyes and picture where each bead is landing around you, yet you never forget that you’re listening to a recording. With the M4U TWM, these sounds take on a much more lifelike quality with razor-sharp resolution.

Despite their otherwise excellent performance, Sony’s WF-1000XM5, Master & Dynamic’s MW09, and Technics EAH-AZ80 — just to name a few — didn’t come close. Only one pair did: the $259 Grado GT-220.

As often happens when I discover a great-sounding set of earbuds or headphones, I got lost in some of my favorite albums, appreciating what the M4U TWM could do for tracks I’ve heard countless times. With the M4U TWM’s support for 24-bit aptX Adaptive (select Android phones only), it seemed the perfect excuse to listen to hi-res tracks on Qobuz.

On Dire Straits’ remasters of Sultans Of Swing and Brothers In Arms, Mark Knopfler’s unique finger-picking guitar style sang out like it was a vocalist. Examining the fine trumpet work in Herbie Hancock’s Watermelon Man was a pleasure. I normally don’t spend much time with Kanye West, but I had a feeling that Stronger’s pounding, bombastic rhythms would sound awesome, and I wasn’t disappointed — the M4U TWM’s commanding bass response was perfectly suited to the task.

Normally, I don’t delve into the science or research that goes into making a set of headphones or earbuds — I don’t think it necessarily adds to the sense of what it’s like to use a product. However, I’m going to make an exception for the M4U TWM because PSB Speakers isn’t like the majority of audio brands.

Inside the PSB Headphones app — which is almost as spartan as the M4U TWM themselves — there are only four equalizer presets. RoomFeel, Better Dialog, More Detailed, and Tighter Bass.

RoomFeel is the default setting. Since it’s listed with the three other EQ options, it’s tempting to think of it as just another preset. And yet, if you look at the position of each frequency in the five-band equalizer, you’ll see they’re all set to zero dB — in other words, RoomFeel is the M4U TWM’s “neutral” or starting position. You can use the other three options to further tweak the sound, but those tweaks are being applied to the RoomFeel setting.

I bring this up because PSB Speakers and its founder, Paul Barton, have a decades-long history in acoustics research conducted in part at Canada’s famed National Research Council (NRC) facilities in Ottawa. That research resulted in a specific tuning curve for PSB’s loudspeakers — a curve that Barton’s double-blind study participants said they preferred.

RoomFeel attempts to give headphones and earbuds that same sound signature — it’s an approximation of what you’d get if you were listening to a set of PSB Speakers in good listening room. If this sounds familiar, it’s the same approach used to develop the Harman Curve, which has become the most influential tuning guide for headphone companies.

Since I really enjoy the way these earbuds sound, that means I’m among that majority who like the RoomFeel curve. However, it may not be everyone’s cup of tea. If that’s you, the other three presets will give you some variations, but it’s not the kind of granular EQ control that lets you dig deep.

This was especially noticeable after I decided to take advantage of the app’s Audiodo sound personalization software, which I’ve used and enjoyed in the past. It does a really good job of boosting just the frequencies you may be less sensitive to due to your age, biological sex, or other factors.

As before, I liked what Audiodo’s tuning did for the M4U TWM, with one exception: The highs became a bit too strident. Unfortunately, there’s no way to tweak an Audiodo profile once created. Your only option is to run the test procedure again and hope for a different result.

If I’d been able to access the equalizer directly instead of relying on the three available presets, I might have been able to dial those highs back a hair. So that’s one thing I’d change: Give folks the ability to create and save their own EQ presets using all five frequency sliders.

Still, it’s a minor nitpick in the grand scheme of things. In terms of sound quality, I’d still pick the M4U TWM over dozens of other wireless earbuds with or without full EQ control.

Clear calls

The M4U TWM’s onboard mics have excellent voice pickup, which makes them a surprisingly good choice for calls — with some caveats. Though PSB claims it’s using the latest clear voice calling (cVc) tech, there’s very little background noise cancellation. If you plan to use them for calls in busy locations (city streets, coffee shops, etc.) your callers will likely hear a lot of your surroundings.

There’s also no side-tone option. Side-tone lets the earbuds pipe the sound of your voice into the audio mix that hits your ears during calls, which makes for a more natural and less tiring experience.

If you tend to do relatively short calls from quiet locations, the M4U TWM make a good choice, but given their lack of advanced calling features (including Bluetooth Multipoint), you should look elsewhere if calls are a frequent activity.

All-day battery

PSB Speakers claims the M4U TWM will get 8 hours per charge, with three extra charges in the case, for a total of 32 hours — more than enough for an average day. That’s assuming you’re playing at 50% volume, which is reasonable when indoors. From what I’ve been able to tell, these numbers are accurate. The PSB Headphones app will give you a specific percentage remaining for each earbud, though on several occasions, it reported as low as 33% even when fully charged. Still, the buds themselves will speak their battery level when you pop them in (high, medium, low), so you’ll always have a sense of where you’re at when you start listening.

If you need your wireless earbuds to perform modern feats of techno-wizardry like active noise cancellation, transparency, spatial audio processing (including head tracking), or the ability to connect to multiple devices simultaneously, the PSB M4U TWM aren’t a good choice. You can spend far less and get far more — Soundcore’s Liberty 4 NC are a great example.

However, if you’re on a mission to find the best possible sound at the lowest possible price, the M4U TWM hit that target better than any other wireless earbuds I’ve tried.

Editors’ Recommendations