In 2012 the famous loudspeaker designer Paul Barton, founder of PSB Speakers, launched his first ever headphone, called the PSB M4U 2, priced at $400. The M4U 2 was versatile with a capital ‘V’, so that it offered three operating modes: a very good sounding passive mode, an even better sounding active mode, and an effective, musically sensitive noise cancelling mode. No matter what one needed or wanted a headphone to do, the M4U 2 seemed ready to fit the bill with no questions asked.
When I reviewed the M4U 2 headphone for Playbackmagazine I called it a “headphone for all seasons” and observed that it was “one of the most cleverly conceived, well executed, versatile headphones that $400 can possibly buy.” Understandably, the M4U 2 sold like free Guinness on St. Patrick’s day and went on to become a great commercial success. Even so, time waits neither for man nor for classic personal audio products so that in 2018 PSB decided it was time to launch a successor to the M4U 2, the wireless Bluetooth-enabled, noise-cancelling M4U 8.
At first glance, the temptation is to look at the M4U 8 and think, “Oh, it’s basically a Bluetooth-enabled version of the original M4U 2.” In a sense that synopsis is partly right, but if you look deeper you’ll discover there’s more to the story than at first meets the eye. To understand what I mean by this, it helps to survey carefully the differences between the models.
The original M4U 2 was a high quality passive/active/active+noise-cancelling headphone driven by a switch selectable, onboard, battery-powered amplifier and that featured an effective, switch selectable, and music-minded analogue noise cancellation circuit. We felt—as did many listeners—that the M4U 2 sounded best with its active mode engaged, but with noise cancellation switched off. This was because the M4U 2’s noise cancellation circuit, though quite good, involved some audible tradeoffs between noise reduction effectiveness and overall musical transparency.
The M4U 2 also offered voicing that introduced what Barton then termed “in-room feel” (and now calls RoomFeel™, used as a marketing descriptor); that is, headphone voicing that mimicked the sound of a comparatively neutral loudspeaker as heard in a listening space offering an average amount of ‘room gain’. In many respects, this voicing strategy was and still is the secret to the success of Barton’s headphones; when you put PSB headphones on they immediately sound much the way you wish your loudspeakers could. In sum, the M4U 2 was a good passive headphone, an even better active headphone, and a very good noise canceller that, while perhaps not the last word in noise reduction, did relatively little harm to the music at hand.
On paper the M4U 8 initially seems similar to the M4U 2; it is roughly the same size, weight, and price; it uses similarly sized dynamic drivers and a similar though not identical frame design; and it provides similar operating modes (a passive mode, an active mode with RoomFeel™, and an active noise cancelling mode with RoomFeel™). The most obvious difference involves the M4U 8’s addition of Qualcomm-based aptX HD Bluetooth connectivity functions, which PSB characterises as “the high fidelity version of Bluetooth”. In addition to wireless modes of operation, the M4U 8 also provides two wired modes of operation via a 3.5mm wired connection, or via “USB from the computer, which recharges the batteries for wireless operation.” The M4U 8 comes with built-in rechargeable batteries, whereas the M4U 2 used conventional user-replaceable alkaline batteries.
As you look closer, though, other significant differences begin to appear—many of them having to do with recent advancements in digital signal processing. When used in active mode, for example, the M4U 8 applies DSP to implement the most transparent sounding and highest resolution version of RoomFeel™ voicing to date. The upshot is that, when powered up, the M4U 8 sounds markedly more open, transparent, focused, and expressive than the original M4U 2 did.