Unique may be an overused word in this business. Game-changing definitely is. But when you take into consideration, and really get your head around Coda Audio's many proprietary technologies, it's difficult to keep your jaw off the floor. It's easiest to let Alexandrov to do the talking.
“OK, first and foremost, we use technology that we built and designed in house, and it is very different to our competitors; for example, all high frequency transducers are with ring diaphragms instead of dome diaphragms, which I'll come to in a second,” he says. “We then have our Planar Wave technology, whereby the driver produces a Planar wavefront without transforming a spherical wavefront coming from a compression driver, like almost every other speaker manufacturer. We do this in just one driver design, which itself produces a planar wavefront.
“Then there is DDP (Dual Diaphragm Planar-wave-driver), another unique technology. Normally, if you see a big line array, you see lows, which could be double 12-inch speakers; then four small speakers for mid range, maybe 6.5-inch; and two or three compression drivers for the highs. But this never gives you a really good directivity; you're using some small mid range drivers which aren't efficient. So what we did is put mid and high range in one relatively small transducer with very high efficiency, and as a result, we get 12-15dB more headroom than the traditional technology, but with a much smaller and lighter design.”
At this point, Alexandrov uses an interesting analogy: the electronics industry in the early '50s, where you had big boards with different electronic components and transistors, and then someone managed to put it all into a small package, which caused an electronics revolution. He wants to create one in audio.
“It's the same principle, really: our package is much, much more efficient,” he insists. What this means, I am told, is that Coda is able to reduce the size and weight of its big systems by around 50%, while actually increasing performance, which sounds pretty crazy to me.
“[laughs] In the early days, a computer was a building... I was in such buildings! But now it's more powerful, and all in one box. Traditional loudspeaker technology is a building, and we tried to do that same thing with our technology: get it into a smaller, lighter format, yet more powerful and efficient. So this is what we have done using DDP.”
Then comes DDC (Dual Diaphragm Curved-wave-driver), a similar technology, but with a bit of a twist.
“With DDC, we don't produce a planar wavefront, we curve the front, and we have the technology to do so,” Alexandrov states. How so, exactly? “Well, normally you have a compression driver, and you have a horn, and the horn makes the directivity - 90- by 40-degree, for example - and it always produces some kind of distortion to reshape the wavefront. With the DDC, we can shape it in the way we want. Take our small format APS speakers as an example: the wavefront is already produced with 20 degrees, we don't need to reshape it and add distortion, and it's much more precise, so when you put more APS together, they perform as one single cabinet; there is no interference between them because of the principle of how it works. Already in the transducer we produce the wavefront we need, so we just add another piece, and another piece.”
The Driving Force
Very smart stuff. But it's Coda's compression driver technology that's probably the most mind-blowing – it's the core of everything, Alexandrov says:
“The conventional dome diaphragm design is very old; it was designed and invented in the '20s, and until today, almost all drivers are working like that. Sure, there are new materials, therefore you can increase power handling and performance, but the basic design hasn't changed in 90 years.
“The problem with a dome is, you have a voice coil, it moves, and then a mechanical wavefront starts to move and reflect back, creating distortion; the diaphragm itself is actually larger than the wavelength. So let's say a wavelength at 10kHz is 34mm, but the compression driver is a three- or four-inch voice coil: at 4-5kHz, it already starts to be incoherent and unstable, as the wavelength is smaller than the physical size of the diaphragm, which means it's very hard to transform that energy into acoustical energy. So what happens is, some pieces of the diaphragm will start to resonate at 10kHz, 11kHz, and so on. What a transducer engineer will do to fix that is essentially like putting a band aid over the fundamental problem: he'll search for materials, perhaps put some coatings on the domes, but it's all cosmetic. You still have the problem, which people have put up with for years.”
And Coda has the answer?
“We do. We put in a ring diaphragm, where all of the pieces of the diaphragm are very near to the voice coil. What that means is, when the voice coil moves, the diaphragm moves as a piston, because the wavelength is larger than the diaphragm itself, which then means we can constantly accept the wavelengths without any distortion – it results in the purest audio you can get.”
But isn't the ring diaphragm a considerably smaller diaphragm than the dome diaphragm?“Actually, no – we have two diaphragms on the ring one: one inside, and one outside of the voice coil, so we actually have a larger diaphragm than a dome,” Alexandrov reveals. “But still, all of the pieces of the diaphragm are very close to the force, which is the voice coil; and this is how we tune the diaphragms: the higher frequencies are produced only from one diaphragm, and on the lower range, both are working in phase. This has helped us to increase the frequency range of the driver, as we are actually driving two diaphragms of two different sizes with the same voice coil.”
As I try to compute this, I realise I'm almost sold without even listening to the kit, or for that point, any evidence that it can do all Coda says it can. I explain this to Alexandrov, at which point he begins to talk about sound quality, and why we as humans perceive something to sound good, and not so good. Not entirely sure where he's going with this, I decide to sit back, and listen on.
“An engineer measures frequency responses, and with modern DSP, you can tune all speakers with the same frequency response. It could be a €100 or €10,0000 speaker, but with the same frequency response – so why does one cost 100 times more? Well, frequency response is obviously not sound quality; you measure some distortion, perhaps they even have the same distortion, or even a speaker with more distortion sounds better. But why? This is the intermodulation distortion, which is very important, and difficult to measure; the coherency, which are the resonances of the diaphragm; and the time domain. What mostly measure the electrical domain, and the acoustical domain; but in the middle is the mechanical domain, which is not very well researched – and distortion and resonances happen there, also.
“Also, with a dome diaphragm, you need to use some special materials like titanium or neodymium, which are light and strong, but because it's a long distance from the voice coil, you still need to use some heavy stuff. There are two different ways of designing this: some companies will use light aluminium domes, which are better, but when you apply a bit more power, they produce distortion, and everything gets crushed; other companies take slightly thicker titanium domes, which is more stable, but heavier, so you can apply a bit more power, but you have other problems, because of the moving mass. What we do, because the distance to the voice coil is very short, is use very thin and strong polymers, which means the moving mass is less, and the efficiency is high.”
How high, exactly?
“We don't have any driver less than 35% efficiency, and we can be as high as 50%, compared to 15% from the competing manufacturers. Because of the efficiency, we have applied less power to achieve it, too.”