Manufacturer: PMC - UK
Reviewer: Maarten van Casteren - TNT UK
Visited: May 2011
PMC, the Professional Monitor Company, is an English loudspeaker manufacturer based in Luton. They've been around for more than 20 years now and have a very good reputation for both professional loudspeakers as well as domestic ones. As far as I know, they're the only major manufacturer still making transmission line loudspeakers, so since Luton isn't very far from Cambridge I thought it would be great to visit the factory and perhaps review a pair of their speakers. PMC agreed and kindly invited me for an afternoon.
The PMC building cannot possibly be called glamorous from the outside, and from the inside it has a very industrial feel and makes the impression of having grown quite organically to its current size. One has to go up and down stairs, through small corridors and even outside to reach all parts of it. You could say it reflects the no-nonsense, partly pro-oriented spirit at PMC to not spend money at things that aren't really necessary, but more about this later. The 'marketing space' at the factory certainly showed some interesting speakers, with the gigantic BB5XBD-Active professional monitors dwarfing a pair of domestic floorstanders.
I was met by Keith Tonge who proceeded by showing me the factory. This isn't huge, as PMC mostly assemble parts that come from other manufacturers. Don't think this means that they just put standard drivers in boxes, though. All drivers are made especially for PMC, to their specifications. And the most famous driver, the dome midrange, is made by PMC itself, on the premises. All crossovers are obviously also made by PMC on site, and with great attention to detail, I have to say. The cabinets are made elsewhere, however, by a dedicated company, and all amplification and filtering for the active speakers is designed by PMC and Bryston and then made by Bryston. PMC has a long relationship with this Canadian amplifier manufacturer and also imports and distributes Bryston products in the UK. They prefer to leave the amplification to the specialists at Bryston and focus on speaker design themselves.
So, what remains to be done in Luton is mostly soldering and screwing the parts together and boxing them up, you'd think. Not so with PMC. First of all, everything that comes in is graded, to the last resistor and capacitor, everything. Parts that are too far out in their measurements will be discarded, the rest is stored by graded value. This not only enables PMC to build very well matched speakers, but it will also allow them to provide you with a perfectly matched part, should your speaker ever need one. This is possible because records are kept of all speakers produced, with the precise values used for all components for every individual speaker! This perhaps seems a bit over the top for a domestic speaker, but is vital for the professional market. And it even doesn't stop there. After assembly all speakers are tested and then first compared to a reference speaker by ear and then again compared to each other within designated stereo pairs. This guarantees that every pair of PMC's will match perfectly and sound precisely as intended.
After we'd seen the main assembly hall where all this happens Keith takes me to a smaller room where the dome midranges are being manufactured. This is all done by hand with utmost precision. The domes are doped twice and have a special double suspension to minimise distortion. A nice detail is that the tool used for doping the domes actually contains a bearing from a Rega turntable! Keith explains that they needed something that would turn very smoothly, so a turntable bearing seemed the natural choice. All parts of the dome mid are custom made, including the bit of foam inside which was designed to precisely dampen the resonances that are inevitable in such a small enclosed cavity. It looks deceptively mundane, but Keith assures me that the foam is specially formulated for this driver and a vital bit of the design. What is certainly very impressive about the midrange is the magnet, which is absolutely huge. I've seen many woofers with smaller magnets. This is because the dome uses a short voice coil in a long magnetic gap, a superior solution but one that requires a rather large magnet.
When we've seen the factory it is time for me to meet the boss. Peter Thomas is the owner of PMC and the chief designer of the speakers. He simply exudes enthusiasm for PMC speakers in general and transmission lines in particular. I ask him why PMC sticks to the transmission line principle, as this is more or less unique in the current market and relatively complicated and expensive to build. Peter answers that transmission lines simply produce the best bass. The whole aim of PMC is to produce a speaker with minimal distortion, no more, no less. That sounds simple, but it isn't. The natural choice might seem a sealed enclosure, but Peter explains that this makes the driver work harder, which creates distortion especially at higher volumes. A ported, 'reflex', speaker is out of the question too, as this just adds a resonator which can never extend the bass with enough precision. That leaves the transmission line, which combines lower distortion than a sealed enclosure with more bass extension than a ported speaker, at least according to Peter. The aim is both to give the bass driver the freedom to move while also adding deep bass through the the transmission line, all of this without introducing unwanted resonances. The problem is that designing a proper transmission line is complex and difficult. As Peter tells me: "A good transmission line can sound very good, but a bad one can really sound very, very bad indeed". Because of this PMC have developed software tools to simulate transmission line speakers, but according to Peter this only gets you to about 70%-80% of where you need to be. The rest is done by trial and error, and a lot of listening. PMC do an enormous amount of listening, to all sorts of music and in a large variety of rooms. This, they claim, is the only way to develop speakers that will work well in all circumstances. A specific role, again, is reserved for the foam used to dampen the transmission line. Precise damping is crucial to get the right results, and in most speakers 2 or 3 different types of foam are used in different locations to get the correct result. The photo shows Peter posing next to a Fact.8 speaker, showing the typical transmission line interior with all the different bits of foam.
In all discussions the thing that keeps coming back is distortion. No matter if it's an active or a passive speaker, a professional or a domestic model, a big one or a smaller type, the aim is always to reproduce as much of the audio spectrum and dynamic range as possible with the lowest distortion. I didn't expect this, as most manufacturers always go on about how much they care about music, emotion and value for money. Keith tells me that this is all very nice but in order to reproduce any style of music in any sort of room you will need a speaker that simply reproduces the signal with minimal distortion. All else will just bias the reproduction towards certain music styles or listening environments and make it less universal. This, obviously, is even more true for the professional market, which demands a top quality tool that will perform consistently well.
Another typical PMC approach is a quite pertinent refusal to be too tweaky. They have reluctantly added bi-wire terminals to their speakers, but the cross-overs are still made from normal, good quality components without any expensive 'boutique' capacitors or enormous inductors. Actually, they use Solen MKP on the locations where it counts, and bipolar elco's where they can get away with it. Air core inductors are not used much, mostly because PMC have found that in many applications a ferrite core actually sounds better! PCB's are reassuringly thick and solid and sport the biggest and fattest copper tracks available to mankind.
Keith claims that PMC is the most used speaker in the top end of the pro market, like mastering, classical recording and movie scoring. when I point out that there are a few other brands that also claim some professional connection his response is surprisingly emotional. He mentions a whole list of famous studios, artists and mastering engineers using PMC speakers and claims that nobody else can even come close. One of the reasons for this is the low distortion approach, another is the range of active PMC speakers available. Nothing can beat an active speaker, Keith states, and the combination of PMC's expertise in speakers design with Bryston's experience in electronics will guarantee a superior product. There are certainly many well known names listed on the website, so I have no reason at all to doubt PMC's claim.
The only real disappointment of the visit is that I cannot audition any of the products on site. PMC have a space for this, but currently they are in the process of installing new amplification and the system isn't in a state to be used. Luckily I leave the factory with a pair of FB1i signature speakers, so that I can at least experience the PMC sound at home. More about this soon, I hope.
I very much enjoyed my visit to PMC and I was impressed with their approach. Honest, down to earth, slightly idiosyncratic and quite obsessed with making the best possible loudspeaker they can, it comes as no surprise that they are doing very well at the moment, even in these difficult times. Let's hope they will still be around for a long time, proudly flying the flag for the transmission line.
© Copyright 2011 Maarten van Casteren - www.tnt-audio.com