Review: PMC twenty5.21i – Passive Compact Bookshelf Speakers

Review: PMC twenty5.21i - Passive Compact Bookshelf Speakers- The twenty5.21 is proof that great things come in small packages. Don't let its compact size fool you; this loudspeaker is nothing less than remarkable.

“Transmission Line” and “Studioabhöre” – it doesn’t even need the additional reference to the United Kingdom for most readers to see the three letters PMC in their mind’s eye. Incidentally, the noun is the omen here: the “Professional Monitor Company” maintains its own “Home Audio” line, which our guests, the PMC twenty5.21i passive speakers (3,290 euros), come from, nonetheless in Biggleswade, north of London, it is important to note that this is given no different sound tuning than the “Studio” series, which is aimed at the professional area.

Whistle inside: the Transmission Line

The PMC twenty5.21i measures just 34 x 16 x 28 centimeters. One wonders how the advantages of a transmission line on the bass side can even be integrated into such small loudspeakers; as a quick reminder: Unlike bass reflex systems, there is no Helmholtz resonator here, but the principle of an organ pipe works. For this to work, the length of the “whistle” must be a quarter of the sound wavelength that is to be acoustically supported. The English have squeezed a multiply folded, 1.3 meter long bass sound duct into their small twenty5.21i, which would normally lead to support at – not exactly sensationally abysmal – 65 Hertz.

Through the defined use and the specific positioning of acoustic foams as well as through the geometry of the sound guidance optimized by PMC, the aim is to influence the acoustic behavior of the air inside the housing in such a way that a tuning frequency of 42 Hz, which is much further south, is possible, as Marketing tells me -Chef Keith Tong explained. Converted, this corresponds to an acoustically effective transmission line length of 1.72 meters.

Pretty robe made of HDF – the loudspeaker housing

Speaking of the case: the English company uses HDF here – with a thickness of 15 millimeters for the baffle and 12 millimeters for the rest. The choice of material for the housing directly influences the sound, and last but not least, the finer structure and, therefore, the possibility of more precise processing compared to MDF is appreciated. According to Keith Tong, the different qualities of different suppliers could also be heard in blind tests. To increase the rigidity and long-term stability of the housing construction, the outside and inside of the PMC twenty5.21i are veneered. The English also pay attention to quality where it is not presented as an obvious selling point.

Which, of course, does not rule out the fact that the PMC twenty5.21i are very well made on the outside: Of course, the mitered glued side walls with their sharp edges are mean standard, the exceptionally neatly applied walnut veneer is a feast for the eyes, the structures of which are of course matched for both loudspeakers.

Nicely balanced

The twenty5.21i are also technically matched in pairs, PMC promises: After leaving the production lines, each loudspeaker is subjected to a listening comparison with a reference model, flanked by further measurements. A low channel deviation, usually within a tolerance of 0.5 decibels, enjoys top priority. We will hear what would actually pass as a very good value and should not least be reflected spatially and acoustically.

I also find it acoustically valuable that the drivers, which are perfectly fitted into the baffle, are held in place by openly accessible screws with machine threads. The sensitive(!) tightening of the screws pays off quite regularly in terms of sound with loudspeakers. This is also the case with the PMC twenty5.21i, as I found out after the first few listens. For passionate Allen acrobats, PMC even specifies the torque, very commendable: 0.6 Nm for the tweeters and 0.75 Nm for the cones.

rear views

Let’s stay with the exterior for a moment and briefly inspect the rear of our British guests, which adorns a metal plate on which the crossover resides directly – and is directly connected to the binding posts. A reduction in detours that PMC sees as sonically significant.

The pole terminals are not homemade, as with my Wilson SabrinaX, but they are designed according to specific specifications. Of course, the matt rhodium coating does not increase conductivity, as rhodium is known to be a poorer conductor than copper. Still, it increases mechanical stability (“abrasion resistance”) and corrosion resistance. Users of speaker cables with spades will also appreciate the good grip of the terminals.

Total TL special: the bass midrange speaker

Using a transmission line places different demands on the bass-midrange driver than, for example, a standard bass reflex system. In addition, the driver must be precisely matched to work with the speaker cabinet. For this reason, there is no question of off-the-shelf drivers for the PMC twenty5.21i, only a solution tailored to the special requirements.

The membrane of the 14-centimeter cone consists of a glass fiber fabric, which PMC attributes to the positive sense of characterlessness or high neutrality. An inverted glass fiber dust cap and long-throw voice coil with a ventilated carrier should also guarantee minimized distortion values. A deflection interruption in the direction of the maximum deflection of the driver caused by stiffening of the centering spider protects against damage at excessive levels. It acts as a kind of “soft clipping”.

Must bend properly: the tweeter

The tweeter, manufactured in cooperation with SEAS, also has to deal with working conditions that are by no means every day. Although separated with a steep edge, it must still be used from a very low 1.7 kHz. In particular, PMC is aiming for an optimized radiation behavior to avoid breaks in the area of ​​the driver transitions and for a wide sweet spot, which is to be expanded even further by the grid in front. The “Sonomex” coating of the cone material also contributes to the Sweespot. According to PMC, the calottes can be manufactured with particularly low material thickness and mass tolerances, which benefits channel equality.

The low crossover frequency seems all the more daring considering that the small 19 mm domes fidget in the PMC twenty5.21i, which are each supported by wide 34 mm beads. In this way, PMC wants to combine the wide dispersion of a small dome with the mid-range reproduction, sensitivity, and SPL capabilities of a standard 1-inch driver.

PMC twenty5.21i: sound test & comparisons

Applause, applause… the space

“I’m not interested in where the musicians stand, but in what they do,” said our unforgotten colleague Markus Sauer once. On the other hand, I know from my colleague Jochen Reinecke that he appreciates a clean room as an indispensable part of his musical meal. I place myself somewhere in the middle.

A good example of the diversity of listening tastes. And for how unhelpful it is to put “objective end-notes” on audio components in tests. However, I’ll make an exception and award at least a partial grade: The PMC twenty5.21i deserve a 1 in spatiality – with an asterisk.

Talk Talk’s cult Spirit of Eden is an exceptional album in terms of interpretation and recording technology. It allows me to witness the musicians with its live-like illusion of space. The PMC loudspeakers take this effect to the extreme. I immediately believe the loudspeakers, which are meticulously matched according to the manufacturer’s statement, our guests are the same pair. But not only do the stereo channels appear perfectly balanced but also the teamwork of tweeters and mid-bass drivers – the small PMC play as if they were made of one piece and appear extremely (phase) coherent.

In practice, this means: Mark Hollis’ voice, sustain-rich electric guitars, noisy drum brushes, fine cymbals, lonely piano strokes, rimshots, etc. pp. manifest themselves so tangibly in the room that one would like to applaud in the middle of the piece. Mark Hollis is given a wonderfully haunting presence. All actors appear coherently coherent and plastically reproduced, as well as being realistically localized and differentiated from one another in the overall view.

I also like how the sound expands generously, far beyond the speakers. And even more so, how it moves towards the listener, developing a nice depth: if the music came from below, I would feel able to jump into the music like a deep swimming pool. Even instruments sorted hard right and left in the stereo panorama do not stick to the box in terms of hi-fi but seem to have nothing to do with their sound sources – instruments, and boxes are two different things on the perception side.

The transient reproduction of the PMC twenty5.21i, which is also an important point for my listening taste, also indicates a phase-correct interplay (keyword: time correctness) of high and mid-bass drivers: Short impulses are defined in an exemplary unshakeable way in the stage design, seem physically tangible.

In all of this, it is commendable that the PMC twenty5.21i do not force you to sit in the best listening position or exactly in the middle between the loudspeakers. They create an amazingly coherent, credible spatial illusion outside the optimal sweet spot.

Precisely to the point

It is only logical that the fine dynamics also have a say in the excellent transient reproduction mentioned: And so in Current 93’s “A Song for Douglas After He’s Dead” (Album: Thunder Perfect Mind), the plucked tones reminiscent of a ukulele come on the attack and sustain side extremely well defined. Even the occasionally shimmering light hits on the wooden body of the accompanying Western guitar give the PMC an – albeit subtle, yet audible – impulsiveness.

Therefore, the tweeter and midrange of the PMC twenty5.21i are of the fast variety. The upper registers are exceptionally open and airy, which further promotes a slight increase in listening psychology: I would classify the treble as a whole on neutral’s fresh, concise side.

It’s little wonder that the resolution is also at a high level. About the reproduction of tangible, “countable” details, the PMC twenty5.21i easily keeps up with my Sehring 903 and all the other loudspeakers mentioned here in the test – or, depending on listening taste, are ahead by a nose, because the PMC structure sound textures even more defined, so to speak with an even harder pencil than the Sehring. On the other hand, hits on the bell of cymbals do not seem so ethereally shimmering, and hard-hit cymbals or hi-hats seem a bit more brittle, less silky than I am used to from my 903, which also play extremely low distortion and fine-pixelated in the treble. Ergo: The PMC tends to speak clear and distinct words at the top rather than attaching importance to

All in all, they join the ranks of the fresh Brits à la Neat Petite Classic or B&W 705 Signature and top the latter loudspeakers when it comes to reproducing the super treble. The PMC sounds the most airy towards the top, appearing limitless. On the other hand, the increased purity of the tweeter impresses with the NEAT.

Off to the south – the bass

The PMC twenty5.21i can also have a certain “limitlessness” at the other end of the frequency range. The bass depth is astounding for such small, compact loudspeakers; even the bass drum in Isis’ “So Did We” (album: Panopticon) is still fished out quite extensively by the English women. Not even many large compacts can do that. The same applies to stability: The PMC will probably not be fully exhausted in multi-family houses.

There’s no question that the twenty5.21i has reference status in its class, given combining the two last-mentioned points. I would have liked to compare them to the GoldenEar BRX in this regard, which also impressed me very much on the bass side at the last North German Hifi Days. In all of this, the PMC acts almost as dancingly as the Neat, which has a wonderfully light-footed (but less deep-reaching) bass and is noticeably more precise than, for example, the B&W mentioned or the Bryston Mini A Bookshelf. The repetitive, short interspersed bass drum sixteenths in “Defaced2” by Résistance (Album: 8) deliver the PMC as well as in “My Name is Mud” (Primus, Pork Soda) by Les ClaypoolThe tedious and precisely played bass is so contoured, clean to the point and dynamically jagged that one can only nod approvingly to the beat.

Incidentally, tonal cosmetic tricks such as sprayed-on bass or fundamental tone cheeks are conspicuous by their absence in the PMC twenty5.21i, which, not least, benefits monitor-esque midrange and voice reproduction. Be it needy male voices like Primus or clear female voices like Laura Veirs in “July Flame” (album of the same name): the high transparency and tonal balance of the mids – with a minimal pinch of crispness in the reproduction of sibilants and F-sounds – show clearly shows that the genes of the twenty5.21i come from the studio area.

Incidentally, like the PMC, the Neat Petite also sheds a little more light on the upper edge of voices but is more withdrawn with sibilants than our current guests. The B&W 705 Signature, on the other hand, is, to put it bluntly, tuned inversely to the PMC on the midrange side: the upper midrange appears slightly weakened in level with the B&W. Nevertheless, listeners who prefer warmly lined, sumptuous mids should immediately grab speakers like the Bryston. The Canadians also deliver a not entirely neutral but beautifully full-bodied, wonderfully sensual quality.

Borderline music and brave minis

Bass and transparency – we had already eaten the points. Still, I must bring them up again when I put Devils in My Details by ohGr or the album’s first three tracks in the playlist. Is that still music, or can it go away? It doesn’t matter; it’s a strenuous challenge for loudspeakers and determines one or the other listener – and undoubtedly a veritable test touchstone, especially for such small speakers as the PMC twenty5.21i.

The way the brave minis follow the opaque, woven, massive sound textures that demand the entire frequency range down to the smallest ramifications is worth a standing ovation. Such tracks also underline that the PMC can be used to listen extremely deeply in musical structures, especially in important mids. Even on good systems, they often leave more question marks than the crude sound already does. Devils in My Details sounds noisy but not headless – the PMC listeners show that in an exemplary manner.

Good reason number two for standing ovations would be that the small mid-bass drivers of the PMC twenty5.21i manage not to appear overwhelmed in terms of gross dynamics with these lush sound loads. This applies even if you hear well above room volume. Despite the pick-packed mids, the bass remained clear – and vice versa. The electronic drumbeats in the song “Eyecandy” also come around minute four in an extremely confident manner: dry, powerful, and full of content, as it should be. With a view to the coarse dynamics – and bass authority – you would have to try compact loudspeakers like the Pearlists R5m to make significant progress here.

Important, however: As mentioned, the PMC twenty5.21i do not puff out in any way regarding tonality. Due to the fresh treble, they even feel rather slim at the first hearing when set up freely. So please don’t lump the aspects of “rough dynamics/bass authority” (here, the PMC get down to business for their size) and “overall tonality”! By the way: The PMC is a good idea to try positioning them closer to the wall; many people may even like the tonality better.


“For listeners who want to know exactly” – this could be an appropriate slogan for the PMC twenty5.21i. In any case, the studio genes of our subjects can be heard. This pleases the sound engineer and the listener, who likes to be excited by the richness of detail and the dynamics of hello and wake up when listening to music. And we are only too happy to do without embellished tuning trickery: the treble of the twenty5.21i seems quite pronounced and is trained more for clear structuring than for accentuated subtlety. On the bass and fundamental tone side, the English developers have dispensed with any level cosmetics; the lower ranges add themselves to the monitor-esque mids in an exemplary neutral way.

On the other hand, the low-frequency reproduction of the PMC trumps all the more with honest qualities: In terms of depth and coarse dynamics, the little ones even outdo some much larger loudspeakers. And when it comes to “spatiality,” the PMCs top many other similarly designed monitors with great imaging qualities: here – and in the bass range – the PMC twenty5.21i marks benchmarks in their class.

The PMC twenty5.21i are characterized by…

  • high transparency from head to toe.
  • Very “fast” fine and coarse dynamics.
  • An astonishingly deep bass, especially considering the dimensions of the cabinet. Which is not least beneficial to the audible impact of the coarse dynamics. Here the PMC offers exceptional qualities given its size and price range.
  • Despite the comparatively mature bass tuning, an almost slim rather than warm overall tonality at first hearing and when set up freely.
  • An exemplary, airy, fresh treble tuned more to the unmistakable elaboration of structures than to emphasize delicacy or suppleness.
  • Highly informative and best-differentiating mids with realistic, by no means embellished warmed tones; Voices that rise upwards are pronounced, “thickening” on the fundamental side is conspicuous by its absence.
  • An extremely clean three-dimensionality, among other things, speaks for a high level of channel equality and phase coherence. When it comes to “stage,” the PMC twenty5.21i certainly takes on something of a benchmark role in their class.


  • Model: PMC twenty5.21i
  • Concept: 2-way compact speaker with transmission line
  • Price: 3,290 euros/pair
  • Finishes: walnut, oak, satin white, diamond black
  • Efficiency: 86.5dB/W/m
  • Nominal Impedance: 8 ohms
  • Dimensions & Weight: 16.2 x 34 x 28.4 cm (WxHxD), approx. 6 kg
  • Guarantee: 20 years