It's rare that hi-fi writers get to talk to the senior design team of a major loudspeaker company. In audio journalism, much of the contact with manufacturers goes via public relations people or the marketing department. As crucial as these people are, they're not at the 'coal face' of product design. The following feature is a sometimes quite technical discussion between myself and the guys who actually do the designing for Monitor Audio – Product Design Director Charles Minett and Technical Director Michael Hedges.

Charles joined Monitor Audio on the 1st November, 2003, as part of the Research and Development team. "I was the first in-house product design team member because the former Technical Director saw the need for having both design and acoustic development under one roof", he says. "More and more acoustic teams were having to hire design consultants, and having a design team that could understand the hi-fi market – which is very nuanced and specific – was better to have in-house than out. We've built the team from there; we have Matt Sharp, who's been there nineteen years, and Joanne O'Connor, who's been here eighteen years."

Michael is Monitor Audio's Technical Director. "I run the Research and Development team, with about forty people now spread across China and the UK. We have about five engineers in China who work with our suppliers. I came into the company as a placement student in 2007 and worked under the previous Technical Director, Dean Hartley, for a year, then came back after university. I became manager of the acoustics team in 2012, then moved to Jaguar Land Rover in 2015 to head up their audio strategy. There, I worked with Meridian Audio and JLR, developing audio for cars, and then I came back into my current role in 2018, so I've been around the business for a while. I joined just when we launched the first generation of our Platinum speaker."

BOXING CLEVER

I start by asking Michael the most basic of questions about the challenges he faces at the drawing board, so to speak. He replies: "With loudspeaker design, we might have a few hundred variables in front of us, and we're throwing them up in the air, and you've got to catch the ones that matter, and that's the sound quality, aesthetic appeal, safety standards – you've got to spend the money in the right place. So when that's a Monitor Audio Bronze series speaker, it means narrowly focusing on the things that really, really count. When that's the high-end Platinum, you can afford to spend the money on things that don't matter so much because there's more budget. The way we engineer as a group, we have a very clear idea of how we should be doing that…"

Monitor Audio Bronze 50

He adds that the very first conversation is about what the speaker should achieve in its intended market. "This absolutely drives the decisions we make. How big it is going to be, whether it should be a 2-way or a 3-way, how big the bass driver should be, the things in it, etc. We also consider how it's going to be used, as most of our customers don't have ideal rooms." Even at this early stage, some choices have already been made – such as the decision to make a box loudspeaker with a bass reflex port. Michael says that, at the simplest level, it's about practicality – getting a solution that works for most people.

"For a speaker with a cone – what we call a direct radiating transducer – you have to separate the front pressure wave from the rear pressure wave, or the two will cancel out, and you end up with no bass. So, the simplest solution is a dipole speaker… You place the drive unit in a large baffle, and it starts to cancel at some point in the lower frequencies – but you don't worry about it too much as you specify very large drive units to solve that. The trouble with this is that you end up with a certain radiation pattern, and it becomes very tweaky; you've got to have it perfectly positioned. When you get it right, it sounds great, but most of the time, they have lots of issues."

He continues: "So when you want it to sound good more reliably, you wrap it into a box, and you protect that rear pressure wave from the front pressure wave so you get no interaction. When done this way, the bass sound isn't so determined by the room. All speakers from that point have some kind of sealed rear chamber, but then you have to ask the question, "What do I want to do with my bass?" Here at Monitor Audio, we want to reinforce that bass and have a speaker that has good bass output down to 40Hz so you cover kick drums and bass guitars properly. And for floorstanders, they go right down to 15Hz for our flagship Hyphn model, so pipe organs and things like that can be reproduced…"

Monitor Audio Platinum 300 3G

Michael explains: "That is why we use a ported box, which effectively acts as another radiator at the lowest frequencies and resonates and adds bass energy to the speaker's output – while still maintaining relative flexibility on where you position it. You can then add horn midrange and treble to that to get higher sensitivity so that small power amps can generate high sound pressure levels (SPLs). But they have natural resonances and natural distortion profiles; horns can distort at the throat at high volumes. So we have stayed with direct-radiating speakers, and we stay with a ported enclosure – and we scale into that good engineering philosophy with very modern, cutting-edge simulation tools."

In other words, according to Michael, the reason why most hi-fi manufacturers make box loudspeakers – as opposed to frame-type panel designs (i.e. QUAD electrostatics) – is because they give very good all-around results in 'real world' conditions. But that doesn't mean they're easy to get right. In the most simple terms, speaker cabinets exist to allow the drive units to do their jobs – and drivers are another can of worms completely. For Monitor Audio, great care is taken in both their design and how they are married to the cabinets. Think of a speaker as a kind of 'Holy Trinity' of cabinet, drivers and crossover, and you begin to understand the multi-dimensional challenge facing designers…

Michael adds: "You can spend a lot of money trying to come up with fancy new cone materials like carbon fibre or beryllium that push the driver's break-up modes higher up the frequency range – or you can achieve the same break-up by using a smaller driver. So, because it's a sensible engineering solution, we make the cone smaller. The trade-off on a midrange driver is that the smaller you make the cone, the less lower frequency energy it is going to be able to handle. But the reality is that if you're crossing over at, say, 300Hz to 600Hz, you don't need a very big cone to hit the maximum SPLs of the bass drivers in that system; the latter are always going to be the things that start to limit first."

CROSS TALK

For the Monitor Audio design team, you might say it's less a case of "it ain't what you do" and more a case of "it's the way that you do it". Michael says the drivers are specifically engineered both for the cabinet they're going into and also for the crossover. "This is the very cutting edge of modern loudspeaker design – before we have any physical parts, we have a simulation of a full working loudspeaker. We have a tweeter, bass driver and crossover network, and we have the final frequency response in-room available to us as a simulation. We go round the loop of adjusting the parameters of the drive units to suit the crossover and vice versa."

He adds: "By engineering the drive unit and the crossover at the same time, we have the ability to, say, cross this tweeter and midrange driver over at 2kHz, 2.5kHz, 3kHz, 3.5kHz, to do it with second order and third order crossovers, to have up to +3dB of boost or -3dB of cut in that region. So when we sit in a listening room, we have options; we don't have issues we have to factor in or workaround. We have the ability to fine-tune our speakers in the listening room. The way we get there is so methodical now. With our latest range, we went in with the second version of the crossover. It was sounding very good, just off the simulated crossovers, so we have the time to fine-tune it from 95% to 99%, to really take it to the next level, rather than playing around at 75% and taking ages to get it to 95%… A lot of our decisions are data-driven, but in the end, it's all about getting the very best experience, and we, therefore, put a lot of time into listening to our speakers."

Monitor Audio Hyphn loudspeakers

Charles says: "Because that system design is happening really early, my team can start working on it really early. We work on everything from the cabinets to the driver chassis to the cone profiles – it's about everything physical on the speaker; all this is done by the mechanical team. The smarter the systems get, the more we can start playing with shapes, knowing where we want flat surfaces and where we don't want them… We don't want to keep repeating the past because we've already done it that way. That's a very easy thing for brands like us to do because we've been around for fifty years, and we're famous for this, that or the other. That's where Hyphn came in - to avoid that pigeonhole of "you're the square box guys who make metal dome drivers…"

Michael adds: "If we find something that's better, then we will go there. I don't think a loudspeaker company should be so dogmatically focused on its past that it doesn't look where its future's going. Hyphn is kind of on that journey; it's a big departure from where we were before. Our job is often to walk in and say, "Why?" why are we doing things in a certain way, to just keep challenging. I don't want to be in a situation where one of my engineers comes up with some amazing cone material and says, "We need to move away from Ceramic Coated Aluminium Magnesium (C-CAM)", and this new thing is demonstrably better, but we don't do it because we're a C-CAM company. So our 'transparent design philosophy' is all about being open to change."

DRIVE TIME

Monitor Audio doesn't make conventional box loudspeakers simply because it always has, and nor will it necessarily continue with C-CAM cones forever because the company happens to use them now. So, whilst it has an illustrious past, with a record of being an innovating company, it's not a prisoner of that past. Charles explains that Monitor Audio was founded in 1972 by Mo Iqbal. "It was very much a cottage industry. Mo was an audiophile who started buying audio components, putting them in boxes, and seeing what came out of it – and that's what the first MA1 speaker was."

Ten or so years later, the company began to reinvent itself by doing more radical designs compared to the more conservative early products. Although Monitor Audio was by no means the first company to use metal dome tweeters, it arguably pioneered their use in the mass market. "1985 was the first metal dome tweeter we used", says Charles, "and it was the gold dome tweeter in 1986. I remember these speakers looking like the future; the R series was snazzy and futuristic stuff!"

Monitor Audio's C-CAM mid driver

Michael continues: "Yes, but those speakers sound hugely different to our modern designs. About fifteen years ago, we moved to single-piece cones from drivers with dust caps, and this was tied up with a big jump forward in simulation technology. We've used the same C-CAM material since almost the beginning – it's a very strong surface coating on magnesium-based aluminium. It makes the surface very hard whilst being very light, with a thickness of just 0.2mm to 0.3mm. Our Rigid Surface Technology (RST) applies a hexagonal dimpled profile to the cone to help adjust and manipulate the modal structure on the cone, improving the strength at certain frequencies. So you have lightness, strength and reasonable self-damping. The latter is further improved by the way we terminate the surround onto the cone, the glues we use and the exact geometry of the surround really affects the break-up behaviour."

Michael remembers: "With the old drive units, we used to sketch a surround, do some testing, maybe you had four or five different prototypes with different surrounds and you'd pick the best one. But now we have moved to full virtual simulations, where we are doing hundreds of simulations of minute changes in surround geometry before we make one prototype that is more than often right first time. So it's a totally different process to the way we work."

He adds: "There are two camps of thought about how you design a drive unit, the soft materials group of people and the hard materials group of people. The soft group say it's better to have a very well-damped material that is not going to be as strong – and they say that we will deal with the problems within the passband of the driver (the usable region) by applying damping. A lot of paper cones have doping over the top of them; they'll have ripples in the frequency response which are generated by break-up modes, but they're small, and you manage them in that manner."

Michael continues: "The hard cone group of people – and we're in this group – say I want no break-ups within my passband, I want to push them all outside of the passband, and I want the crossover to knock them off and deal with them – or I'm going to use other methods. The group of materials that you tend to use are much stiffer and include aluminium, titanium and beryllium; as they get stiffer, they all have much lower damping factors and, therefore, much stronger modes. So what we're trying to do with the aluminium cone is push all those break-up modes outside of the passband – so for a mid/bass driver or midrange driver, we're trying to get it substantially above 3kHz. We feel that the sound of the loudspeaker is better than when you have a speaker where you allow the break-ups in the pass band and try to damp them out. We've now got to the point where we know how to manage those break-up modes outside the passband with a number of deployable technologies. For example, our speakers use smaller midrange drivers than traditionally used, which pushes the break-up really high up, up to 10kHz, so the break-up is reduced by 40 to 50dB."

He says Monitor Audio now uses elliptical crossovers on the latest two-way speakers. "This is a way of managing the break-up, so we don't energise it in the first place. You've got, say, a 6-inch mid/bass driver, so your break-up is going to come down to, say, 5 to 6kHz, so it's only one octave above your crossover frequency. So you need to get the break-up much lower than that so it's not audible, and we have technology to do that."

Michael says: "The actual fundamental components of those first C-CAM drivers haven't really changed, but what they're doing and the way they do it has changed. So we still have a voice coil, a cone, a surround, and a spyder, but the performance you can get out of them by changing their geometry is huge. So you go from what I would call "reasonably unoptimised drive units" to this period today, where the level of optimisation is very high. Those drive units are really pushing the boundaries of what's possible with this technology now. On a 2-way, 6.5-inch bookshelf speaker, you are going to get a break-up on the bass driver around 6 to 7kHz, but when you get to your 3-way floorstander, you get that 3-inch midrange driver with a 9 to 10kHz break-up. That's an extra octave higher, and your crossover might be a 3rd order crossover with an extra acoustic order in there, so you're 24dB per octave, that's 48dB, so you're heading down to inaudibility."

He points out that 2-way and 3-way speakers present different challenges to designers. If you design a 2-way well, then the crossover is quite a simple thing to get right, but with a 3-way, you've got an extra element in the crossover. "So getting it to have the correct phase linearity and the correct tonal balance is a bigger job – because it's an order of magnitude more complicated. Crossing over to a bass driver from the bottom of your midrange driver at around 400Hz to 700Hz is where you've got to put in some real thought. You'd think it's the simple area because you've got a flat midrange driver and flat bass driver, but we have strict rules on what we do with our impedance – we don't want to end up with really low impedance dips. That takes some thinking about."

LOOK SHARP

In terms of aesthetic design – the outward appearance of the speaker – Charles explains that his team gets a set of ideals from Michael's team: "And without compromising his specifications, we have to mould that into something that is home-friendly. It's about getting that understanding of what you can and can't do – so we don't come up with ideas that we know aren't going to work. It's not just about cabinet volume; it's about where those drive units are…"

Michael retorts: "You have got to make speakers that are aesthetically pleasing first and foremost. So yes, we are making speakers that are about performance, that are about music and the experience of listening – but if they don't photograph well, then the customer never goes into the shop in the first place. So we can't just do anything because of performance; everything has to be done hand-in-hand. We're very much a performance-first brand, and the challenge to my team is to 'find the beauty in that'. When you look at all the great products in history, they do the performance first, and the beauty just seems to fall out naturally. What we've been trying to master is to get that into proportion."

Charles continues: "It's not always about performance 'versus' aesthetics - when we get it right, then it's a collaboration that is to the benefit of both. Sometimes, there can be trade-offs. It's about getting people in the door, getting new customers, to experience how our speakers sound. There are two key elements to this process of design. One is to get people to look at our product; they see our products on screens, so we have to make it look great, photograph it well, and entice people to want to go and find out more. Second, when you actually get in that store, you have to convince people that this is something they want to have in their home, and the home isn't just about loudspeakers. I think this is often forgotten about in domestic audio design."

Charles is caught in the middle, then, as he has both an aesthetic and a sound design remit – that's a multi-dimensional job. "It is, and the way you succeed is to understand our customers", he tells me. "What are they thinking about when making these decisions? What we mean by our 'transparent design philosophy' is that we're not trying to make the speaker the focal point of the room. We really want to make sure that what you're listening to is the most exciting and interesting thing, but you're not thinking about the object. We're trying to take away the constant thinking about technology – it just does its job; you're just listening!"

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