Martin Audio MLA Compact

BRAINS BEHIND MLA COMPACT

Chris Holder talks to Martin Audio Research Manager, Ambrose Thompson, about the MLA multi-cellular approach.

Chris Holder: Martin Audio has gone out on its own with this multi-cellular approach. What prompted this ‘line of enquiry’?

Ambrose Thompson: If you cast your mind back to the start of the modern touring line array era, everyone assumed a line array must be uniformly driven – the same signal to every single point. For a long time it was the dominant dogma we heard preached. When Martin Audio began experimenting with line array we realised that approach simply wasn’t flexible enough – because using just the array shape to compensate for air absorption wasn’t always practical. Instead, we looked at our six-channel system controller and contemplated how to get the most out of it. So we decided to split the array into six zones. We used three channels for the HF, two channels for mids and one channel for low frequencies. We found that it gave us a much higher degree of control in compensating for environmental effects and we developed individual settings for different array shapes. That was back in 2001, and the technique we’re using now is a development of what we did then. Really, it started off with the motivation that the users were getting a pretty raw deal – they were handed a whole bunch of speakers and just told to get on with it.

CH: So it was the lack of flexibility of line array that you were responding to?

Ambrose: Sure. When we made our first line array, we put a uniform flat signal through it – like the dogma told us to – and it didn’t work properly. At the time we had no acoustic model and didn’t know what to expect. We ended up with an enormously bass heavy output. We quickly applied global EQ to balance the system and while it sounded impressive in some positions, it was frustrating that the only way we could alter the tonal balance relative to a position was by mechanically changing the shape of a very heavy array.

CH: What next?

Ambrose: We began to think about how best to optimise the array. The first step was getting its shape and splay angles right for the room it was in. We started to apply our ‘numerical optimisation’ to achieve that. 

CH: ‘Numerical’ optimisation?

Ambrose: I qualify the word ‘optimisation’ with ‘numeric’ because ‘optimisation’ is a term bandied around in an inaccurate way. People talk about optimising an array, but what they’re really talking about is manual trial and error. What we’re doing is quantifying the output of the array (or the ‘quality’ of the array) on the audience (and, just as importantly, not the audience) with numbers, and these numbers are optimised.

CH: So you used maths to optimise the shape and splay of the array elements. What next?

Ambrose:: We thought, now let’s try doing a similar thing with EQ. We did an experiment in software and the results – the level of control and uniformity of sound over a designated area – were astonishing. We built some prototypes and eventually we got to the point where we released a product.

CH: The MLA?

Ambrose: Actually, the first system to benefit from this approach was the Omniline, an install product with very small elements and a fixed requirement for coverage. In this application pure shape control and numerically optimised global EQ works well. And, actually the first ever system to use numerically optimised elemental EQ was an Omniline array that [Australians] Glenn Leembruggen and David Gilfilian fitted to the Royal Institute in Adelaide. Then we released the MLA.

CH: And that’s the MLA’s secret sauce isn’t it. You’ve gone a long way to perfecting the EQ optimisation.

Ambrose: It didn’t come easily. We realised that we needed an accurate acoustic model and we needed to do a lot of work to be broadband accurate. The early models were good enough at high frequencies to do the array splay optimisation, but needed fine tuning for EQ. If you don’t know what’s really coming out of your speaker then there’s a good chance you can make it a lot worse.

CH: How did you arrive at the new IndexPlot?

Ambrose: The new plot is quite a nice side effect of our optimisation work. Let’s not forget, there are two domains we’re interested in as system designers: Space (a position in the audience) and Frequency. These were always served too much in one area – you’d have loads of frequency plots in one position or loads of positions at one frequency. 

Part of the optimisation process was to look at all frequencies at the one time, together with this accurate acoustic model. The model needed to be comprehensive and, above all, needed to be really fast – in fact, we can solve the acoustic output of an array at all frequencies in a medium-sized venue in way less than a second, which is one or two orders of magnitude under what is currently available elsewhere.

CH: The plot takes a little getting used to.

Ambrose: But once you’re accustomed to it you’re seeing so much more – what the array is doing throughout the venue at all frequencies. And once you’ve got it into your head, it’s a case of ‘why would you want to look at anything else?’.

Alternatively, most software programs plot the output of a system in the air. You look at a plot, a section view, and it shows you colouring in the air above people’s heads. That’s computationally very wasteful. I mean, who cares what’s going on above people’s heads? 

CH: Are you asking more of the user? Is a more accurate room model required to drive the MLA Compact?

Ambrose: There’s a minimum effort required. You need a reasonably accurate description of the room in 2D. The software was designed from the perspective of a touring user, so we’ve set very tight time limits on how long a process should take. Put it this way, it would surprise me if anyone would take more than 20 minutes to map out a room well enough for optimisation; plug in some defaults; optimise it; and get the results. That was the philosophy behind it: we can’t be faffing around with forensically accurate measurements.

Saying that, I think the system will especially reward those with very specific problems – something they really would like to avoid or enhance. I see that more as a consultant’s job. The consultant has more time to spend, and will be rewarded.

SIDE BY SIDE

The speaker configuration is a little unusual for a compact system. The lows are horn-loaded, while the mids and highs sit side by side. According to Martin, by avoiding the usual co-entrant/crossfiring/co-ax approach the MLA Compact can achieve a far more even and predictable horizontal coverage pattern.