PMC twenty.21

Hardware Review

PMC twenty.21
Wednesday, May 29, 2013
loudspeaker
Jason Kennedy

When PMC launched the twenty series last year my first thought was, I want to hear the big one, the twenty.24 floorstander. After all when it comes to speakers bigger is better is it not. When I reviewed that model I was very confident that this had been proved once again. However, now that I’ve spent as much time as possible listening to the smallest model, the twenty.21 standmount, I’m less sure. This little box is dangerously good.
When Peter Thomas developed the twenty series he set out to make every part of the speaker (except the actual drive units) as inert as possible, the cabinet, the driver chassis and the crossover construction were all looked at with a view to minimising vibration. He used sensors on individual parts and looked at waterfall plots of the signal decay in order to identify what was coming out of the speaker after the signal had stopped. The perfect speaker would stop emitting sound immediately but in reality they don’t, they continue to resonate for many milliseconds afterwards. It is these delayed resonances that are the enemy of speed and detail and it was Peter’s design goal to minimise such artifacts so that it was possible to then hear the benefits of the drive units and components in the crossover.
Both these elements and the cabinets themselves are of a higher quality than PMC used in its iSeries. The tweeter is a 27mm Sonolex soft dome that the company developed in tandem with drive unit manufacturer SEAS. It has a distinctive metal grille that acts type of lens to improve dispersion, PMC is big on dispersion and makes enormous efforts to keep it consistent across the band. That’s why the crossover point is a very low 1.8kHz, it means that where the mid/bass hands over to the tweeter the two have as close a dispersion pattern as possible. The bass driver itself has lightweight doped cone in what the company calls natural fibre, a term that indicates that it’s mostly paper which has always been a very hard material to beat in two-way designs.
The twenty.21 is just over a foot high yet it packs a 1.72 metre (5.5 foot) advanced transmission line (ATL) within its distinctive rhomboid shape. The black foam covered slot at the bottom is the vent for this line and its function is to deliver low bass notes that are in phase with the output from the main driver. The cabinet shape has two advantages, it naturally aligns the acoustic centres of each drive unit and it’s intrinsically very stiff. The only disadvantage is presumably cost of production but it gives the twenty.21 a distinctive look that sets it apart from the crowd. Cable connections are via bi-wire binding posts that are supplied with gold plated jumper bars so it’s not necessary to have bi-wire cables. Cabinet finish is to a very high standard, I had the oak veneer but there are two other veneer options and gloss or ‘Diamond’ black to choose from. Magnetic grilles are also supplied.

 

Sound quality
The chief appeal of the twenty.21 is its remarkable sense of speed. This is an incredibly coherent speaker, so much so that it out performs larger multi-way speakers at rather higher prices in this critical respect. This is undoubtedly related to the work PMC has done to eliminate resonance in the solid parts of the system, resonance that is so common in speakers that it’s a breath of fresh air to find one with so little.
I used this speaker on its dedicated stand which has also had some attention with regard to resonance control, this in the form of a sandwich construction on the top plate with a damping layer in between steel plates. After some experimentation I discovered that while this isn’t a difficult speaker to drive it responds well to amps with plenty of grip, like the Leema Tucana, so this is what was used for most of the listening.
The first thing that hits you is the bass, diminutive speakers have a psychological advantage in that expectations are low so when real bass appears it’s all the more welcome but here it’s different. This is very clean, taut and well defined bass. It doesn’t go all the way down but goes far enough to do the business with the likes of Dub Colossus (Dub Me Tender), this 24-bit recording threw up a massive soundstage that takes over the entire end of the room, the speakers themselves disappear. Next up was a bit of classic bop in the form of Herbie Hancock’s Empyrean Isles album, here the twenty.21 showed me just how incredible the band was by delivering the pace at which they worked without any overhang. The energy they managed to put down on tape was extraordinary and seemingly none of it is left to the imagination with this speaker. Another Blue Note album from the same era, Art Blakey’s Moanin’ lets the speaker show just how different recordings can be even if they came from similar sources, the character of each is loud and clear but it’s the playing that takes centre stage.
A favourite from the seventies, Frank Zappa’s Joe’s Garage, ushers in the fact that engineers had mastered the art of reverb manipulation by this stage. Here the scale was immense but the imaging remained crisp within this context, you could pinpoint instruments and voices within the cavern created by effects. It was also interesting to listen to a familiar song by Steely Dan, I got a box set called Citizen with most of the bands work on recently (it’s an old set however) and it was interesting to hear the way that the remaster of The Royal Scam has been manipulated. It’s a bit more urgent and compressed than the vinyl but nonetheless delivers the emotional goods with this speaker. The twenty.21 is so nimble and agile it’s uncanny. Smaller speakers are always going to have the edge in terms of pace but usually this is at the expense of bass power. Here the bass is both sufficiently muscular and extremely coherent, the timing is second to none.

 

Conclusion
This little speaker is a lot more capable than virtually all the compact standmounts I’ve listened to. The combination of mercurial speed, effortless full scale imaging and decent bass extension for the size makes it irresistible to the discerning music lover. There doesn’t seem to be a music type that it can’t do justice to, there are occasions when more low frequency gravitas would be nice it’s true but far more where the sheer speed and lack of time smear means that you are too caught up in the music to worry about tonal balance.
Add in the attention to detail throughout the design and the first class build and finish and you have a loudspeaker that is very, very hard to beat. There are boutique brands with more caché but you should buy them for snob value alone, if you want to really get involved in your favourite music then I’d challenge anyone to find a better compact standmount.

 

 

Peter Thomas

I asked PMC founder and designer Peter Thomas a few questions about the genesis of the twenty.21.

Of the three models I’ve tried the twenty.21 seems to be the most coherent in terms of speed and imaging, why do you think this might be?

Yes that's interesting! Well all the twenty series have been voiced identically and we've paid a great deal of attention to making everything as inert as possible. The dispersion will be slightly better on the 21 and 23's as they use the smaller bass units and therefore allow us to create a narrower cabinet (a good thing!).

Of all the four models, the low frequencies of the 21 will roll off earliest and this may give the effect of a faster more pacey LF. It's a psycho acoustic effect that leaner and less extended bass can sound faster. Greater low frequency extension can mask detail in upperbass frequencies and appear less agile.

The twenty series stand has a sandwich construction on the top plate, can you hear what this does?

We found that increasing the damping of the stand further and absorbing any residual ringing effects of the stands certainly improves the smoothness of the very top end and in turn sharpens up the already superb  imaging. It's basically more inert!

You use gold bars rather than plates to connect the two pairs of binding posts together, is this for sonic or practical reasons?

Both the terminals and bars are produced by a British turning company and their quality of materials and finish is both sonically and cosmetically superb so we preferred to have them made at the same high quality source.

Given the apparent benefits of the rhomboid cabinet shape is this something you might use with higher end models in future?

Possibly, but the additional internal bracing and heavier construction of the twenty.21 are by far the biggest contributions to the performance. The sloped cabinet was  primarily designed to delay the tweeter signal with respect to the woofer to integrate the two drive units more accurately at the crossover without resorting to additional crossover components.

What is the advantage of laminate core inductors over ferrite ones in the crossover?

They have a much  lower saturation point than the ferrite solid core variety which allows the low frequency to extend effortlessly even at higher levels with less compression and distortion.  Sonically they have more ‘life’ and don’t inhibit dynamics like so many core types. Air cores can be very lossy, so laminate core designs are the perfect balance of high power handling and dynamics.

What is the secret to this speaker’s remarkable sense of speed/absence of overhang?

I'm very pleased you say that as that was the design goal in a nutshell!  We wanted to make everything in the speaker as inert as possible, the cabinet, the drive unit chassis and the crossover construction. We use sensors on the individual parts and produced waterfall plots of the decay of the signal after it had been turned off, the perfect speaker would stop emitting sound immediately but of course in an imperfect world they don’t and continue to resonate for many milliseconds afterwards. It is these delayed resonances that are the enemy of speed and detail. Once we began to minimise these artefacts we could then hear the benefits of using purer components in the crossover and more advanced drive units. It's a holistic approach really as all parts of the design have to increase in performance  together in order to hear the benefits as a whole. Just improving one area is not good  enough!

Do you make any active subs that are fast enough to give the twenty.21 giant slaying bandwidth?

You could certainly add the TLE1 so you could extend the low frequency but if you are looking for the same open sense of scale as the twenty.21 with more giant slaying bandwidth then look at the twenty.23 floostander that uses the identical bass unit or even the twenty.24 which is a true giant killer.

 

Specifications: 

HF drive unit: 27mm soft dome, ferrofluid cooled
LF drive unit: 140mm lightweight doped cone
Quoted sensitivity: 87dB
Quoted nominal impedance: 8 Ohm
Finishes: oak, walnut, amarrone, diamond black
Magnetic grilles
Dimensions (H x W x D): 325 x 152 x 277mm
Weight: 5kg

Price: 
£1,375
Manufacturer Details: 

PMC
T 0870 4441044
www.pmc-speakers.com

Distributor Details: 

USA
The Sound Organisation
www.soundorg.com