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Dave Gunness: loudspeaker design comes full circle

Erica Basnicki 25 March 2013
Dave Gunness: loudspeaker design comes full circle

Dave Gunness is not just an audio engineer; he is an inventor and innovator working in audio. In 2008, after accumulating close to 25 years of experience in loudspeaker design courtesy of Electro-Voice and EAW, he co-founded Fulcrum Acoustic, a company whose vision would be to make loudspeakers with advanced DSP algorithms as integral part of their design.

This led to the creation of Temporal Equalization (It’s trademarked so we’re using the U.S. spelling…- Ed] – and if the latest Gunness-designed PreSonus loudspeaker lines, launched at NAMM, are anything to go by, it might just be a game-changer.   In a nutshell, what is ‘TQ’? Temporal Equalization (TQ) allows us to purify the impulse response of the speaker using FIR filters to do things that you can’t do with conventional IIR filters. It’s at the core of our Fulcrum line and now at the core of both the PreSonus AI and Sceptre lines.   A different way of working with DSP? Well, all of speaker design is about trading off one thing for another, and the leverage you get with DSP means that sometimes you can take one of those things and essentially solve the problem digitally instead of doing it physically or acoustically.   Could you give a specific example? OK, on the PreSonus 328AI PA speaker, all three cones go down to 50Hz, and as you go up in frequency you get to a point where that stack of cones has too narrow a beam, so the outer cones start tapering off, and you’re left with just the little 8-inch cone. The centre 8-inch cone is by itself for only a little less than an octave, and then it transitions into a compression driver. You simply couldn’t design a speaker that way if you didn’t know you were going to have DSP available, because you have to be able to do very particular things with the phase response of the woofers so that when one’s rolling off it sums with the other one.   The PreSonus speakers use a coaxial speaker design… For years, I’d thought about things you could do with coax to make them work better. After forming Fulcrum Acoustic, we worked on a project for another manufacturer to design a range of studio monitors, and though the monitors were very successful, they were much louder than they needed to be, so we realised they would actually make a great contracting product because of their efficiency and stability. We made a whole line of contractor boxes based out of the coaxial work we did on the studio monitors, and eventually we resurrected that as a Fulcrum studio monitor.   Your ‘coax’ designs, and your TQ technology, have been used in both the AI (live) and Sceptre (monitor) designs. There must a lot of ‘personal’ R&D in there too? Somewhere around 25 years’ worth! [Laughs]. It’s based on concepts that date back to the late ’80s at Electro-Voice. I designed their HP horns, and what was fascinating about that project was that each had a different character; it was very consistent even after you EQ’d it, but once you knew the sound of the horn you could still hear that EQ’d speaker. That was when I started thinking about what was causing it and how you could ‘erase’ the signature of the horn, but the technology wasn’t available at the time to do it.   After E-V, you went to EAW in the early 2000s, by which time DSP had moved on too… DSP actually got to such a point where I realised I needed to go back and finally try this thing that I wanted to try for 20 years. It was quite an adventure. It’s easy to say technically that you’re going to purify the impulse response and maybe that will make the horn less distinct, but honestly I had no idea how much it was going to help and in what way. So for the past eight years or so I have been discovering all these little things that TQ can do, and how it sounds, as opposed to how it looks on an impulse response graph.   Everything’s finally come to fruition, then? Well, kind of. Some ideas work, some don’t: you just keep the ones that do, and after a while you find yourself with a pile of 20 or 30 which, when combined, can do something really special.   Were you driven to work in audio from Day One? I wanted to go into aeronautical engineering, but then I discovered it didn’t mean you got to design airplanes, so I moved into electrical engineering! I studied electroacoustics and I was building speakers because I couldn’t afford to buy speakers. Once I graduated, I got a job at Electro-Voice, and funnily enough, the first project I worked on was a coax!   Full circle, then? Yeah – I won’t say it was a great design, but I certainly learned a lot from it.   As this technology continues to evolve, will it become more difficult to predict what the next breakthrough might be? Oh, definitely, as it’s a very deep field. More DSP power would suggest it will only get better, but the challenge is not getting a powerful enough DSP, it’s getting powerful enough analytical tools to figure out what to put in that DSP. That’s where the magic happens: the calculations and listening processes that allow you to develop the magical sequence of numbers that make these speakers sound great.   An uncertain future, then? But if you knew what would happen up front, it wouldn’t be an adventure now, would it?

Story: Paul Watson   www.fulcrum-acoustic.com www.presonus.com

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