What is the PMC twenty5.21?
At the same time, the other influence was making this decision easier. As work on the prototypes progressed, it became clear to PMC that some additional outlay on the speakers – pushing them up in price slightly – would yield some considerable benefits. As such, the twenty5 series occupies the space between the twenty series and the fact series (the crippling shortage of capital letters at company HQ shows no signs of letting up it seems) and while they look like PMC speakers, they are considerably different to what has gone before.
All this does mean that including a pair of the company's own speaker stands, the twenty5.21 now costs a little over two thousand pounds. Given that this sum buys some rather more dimensionally impressive speakers, it asks the question, can all this new engineering and technology deliver a performance commensurate with the asking price? There's only one way to find out...
This stiffness is only part of the changes undertaken. The dust cap in the centre of the driver is now inverted to provide a more even connection to the rest of the driver. Having created a cone that can travel further without distortion or break up, PMC has then mated it with a beefed up magnet and voice coil assembly that can provide the necessary grunt to allow this to happen. The driver is dotted with interesting thinking that stems from years of PMC monitors being driven to the edge of detonation around the world. The 'spider' – the device that effectively holds the driver together – also serves as a sort of manual break so if you do attempt to put the driver into space, it will impede your efforts to do so, not unlike a soft clipping circuit on an amp.
Compared to the mid-bass driver, the tweeter has been less heavily revised but still boasts a selection of modifications to improve performance from its ancestor in the twenty series. The most visible of these is a new mounting and guard that serves the dual purpose of making the speaker more toddler proof and acting as a means to better spread the high frequency information. This is partnered with a new crossover that is mounted on an especially thick circuitboard that features very thick copper tracks to avoid loss and resistance build up.
Like almost all PMC designs, the twenty5.21 uses a transmission line as a means of bass augmentation and this is where some of the most significant changes have taken place. The company has been heavily involved in the process of studying the airflow through the line and as it exits the speaker has made use of computational flow modelling to do this. In the course of this work, some 'pinch points' in the process were identified – and corrected – but a more interesting phenomenon was observed. Air leaving the transmission line had a habit of spiralling on exit creating the sort of turbulence that can be visibly observed with water and other liquids.
To deal with this, PMC has developed a new port which they've dubbed Laminair. This places a series of laminar airfoils in the mouth of the port. These exhibit minimal drag – laminar flow wings are routinely used on aircraft for this reason – but provide sufficient control on the exiting air that the turbulence is obviated. This in turn allows for the greater excursion of the mid-bass driver to be turned into cleaner low end energy than would otherwise be the case.
All of this is then wrapped in a cabinet that looks similar to previous PMC models and includes the very distinctive 'stagger' to the leading and rear edges to aid with the time alignment of the drivers. It takes more of the measurement data to apply bracing at critical points and better isolate the drivers from the outside world. The result is a speaker that is extremely inert considering the small size.
How was the twenty5.21 tested?
Follow this simple, basic instruction though and the PMC will show you a few things. The first is that – for reasons I'll expand on – this is a significant step forward over the twenty series. The second is that the revisions to the transmission line have further bent the laws of physics and put the twenty5.21 in a unique place in performance terms. PMC standmounts have always had superb bass for their size. Where the immutable laws of space and time caught up with them was that on occasions, there would be the slightest sense of sluggishness to the end of some really low notes.
It seems that this sluggishness was the audible effect of the turbulent air at the mouth of the port. The revisions made to the twenty5.21 have resulted in a speaker that still hits far harder than a cabinet of this size has any right to but now does so with an immediacy and agility that moves this speaker on from its predecessors. The potent bassline of Public Service Broadcasting's Korolev is reproduced with real force and drive but still possessing the sheer energy that standmounts excel at.
Perhaps just as importantly though, it still knows how to engage and have some fun. Listening to Wild Beast's He the Colossus on these speakers is sheer brilliance. The low end punch combined with the effortless cohesion top to bottom ensure that this is a tremendously engaging speaker to listen to. Using them with the Naim electronics that are resident here makes for an excellent partnership but the behaviour of the PMC does suggest that these aren't a quick fix to cover substandard electronics. PMC has done a commendable job in terms of the sensitivity and overall behaviour of the twenty5.21 but they are revealing enough to show up the flaws or quirks in your source equipment and will require a reasonable if not excessive amount of power to show what they can do.
Otherwise, the only real stumbling block to the twenty5.21 is that talented competition surrounds – and in one or two cases slightly undercuts – it. With the PMC stands added to the £1,870 asking price, this is a £2,000 speaker system and if you have a larger room especially, there are floorstanding options that will keep the twenty5.21 honest. Having spent some time with the PMC though, if this were my budget for speakers and I was choosing for this normal sized lounge, few other models I've tried at this price point have the sheer ability and 'rightness' in this room and I suspect that this is not some isolated event.
- Superbly powerful performance
- Wonderfully refined top end
- Handsome and well built
- Fairly pricey
- Require careful partnering
PMC twenty5.21 Speaker Review
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