For the vast majority of music lovers the rectilinear shape of a loudspeaker is what defines its purpose; a box with square corners and round drivers is a speaker. So when PMC launched the twenty series five years ago it was taking a gamble: would the more dedicated music enthusiasts, who seem to be a notoriously conservative bunch when it comes to design, go for a box that seems to be leaning backwards? The appearance of a twenty5 series would suggest they did and that the trapezoidal shape met with commercial success. But this is also a little confusing in marketing terms. When the twenty5 series was launched at the 2016 Munich High End show, I presumed that these models would replace the twenty series. But that’s not the case, nor do the two ranges share anything more than the fixings for the tweeter. Despite the similarity of shape and size they are completely different speakers. There are clues to this in the shiny metal highlights on the drivers and the fins in the transmission line vent, and even more so in the price list. The twenty5 series is distinctly more expensive.
The main difference between this latest range and all but one other model in the catalogue is the so-called Laminair vent. This was developed for PMC’s largest professional monitor the QB1-A, an active design with four 250mm bass drivers and frankly alarming fire power. Designer Olly Thomas worked in Formula One prior to joining the company and studied the effects of turbulence on air movement. Turbulence is as much a problem at the opening of a reflex port or, in this case, transmission line as it is when you are looking for ways to make a car go faster. This is most apparent with the QB1 because of the sheer fire power produced by four bass drivers; he discovered that by introducing vertical fins or ‘strakes’ into the mouth of the vent, turbulence was dramatically reduced, which means that air could flow more easily. PMC gives a figure of 60% for the reduction in turbulence and drag produced by Laminair, so the question then becomes when will we see this technology introduced across the range? Sadly the answer isn’t ‘next week’ because it’s not just a matter of putting strakes in the vent of an existing model, as the whole bass system has to be redesigned. But given the results achieved with the twenty5.22, I’m looking forward to hearing what this will do for my fact.8s.
This is one reason for the new mid/bass driver on this range. For the first time PMC have adopted a woven glass-fibre material rather than paper for this task. This material was chosen in order to provide sufficient stiffness to cope with the higher pressures created by extra damping material in the line, it also allows for higher sound pressures, AKA higher volume. On the twenty5.22, this is a 165mm example of the breed with an inverted glass-fibre dust cap and a long-throw voice coil with a suspension system that provides excursion braking for the purpose of avoiding damage to the system if it’s pushed too hard. If you need that much level, I’d suggest a larger loudspeaker! The tweeter is a refinement of that found in the twenty series with the addition of a perforated grille designed for optimum dispersion. The crossover is built on thick glass fibre board with chunky copper tracks and a 1.8kHz crossover point. It sits behind an attractively shiny non-magnetic, stainless back panel that bears just a single pair of terminals. But they are lovely terminals: custom made in rhodium plated copper, they are a match for the best in the business. The reason given for the single pair is that it reduces signal path lengths, but what they don’t say is that the bridging plates provided with most bi-wire terminals are a serious compromise. Although bi-wiring can be advantageous in some systems, I always prefer one run of the best cables I can afford rather than two at half the price.
PMC makes a dedicated stand for the two bookshelf designs in this range, which also leans back and has two columns supporting top and bottom plates that are a sandwich of steel and damping compound to minimise ringing.