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Drivers in Demand as Materials, Designs Change

New technologies and materials are helping to drive improvements in efficiency, fidelity and weight—if not always cost—not only in cone speakers but also compression drivers, while at the same time bringing about a revival of some classic designs.

The essential design of the cone loudspeaker has remained largely unchanged since the early 1920s, when it was patented on both sides of the Atlantic. That said, new technologies and materials are helping to drive improvements in efficiency, fidelity and weight—if not always cost—not only in cone speakers but also compression drivers, while at the same time bringing about a revival of some classic designs.

Celestion, based in the U.K., has been manufacturing speakers ever since Eric Macintosh went into production with his patented transducer, known as The Celestion, in 1924. “It’s true to say that most of our customers and the market are fairly conservative and don’t really like change too much,” remarks Paul Cork, head of engineering. “A 3-inch titanium dome compression driver is a fairly tried and true unit, and there are some that wouldn’t want to change from that.”

Celestion has developed a reputation as a reliable manufacturer of consistent quality products over those past 90-plus years, adds Ken Weller, product marketing manager. “We sell vast amounts of compression drivers—something like 1,000 a day. It’s all very well making 100 or 1,000 compression drivers all exactly the same, but making hundreds of thousands all the same is actually a really difficult thing to do. It’s something that we’re successful at.”

Yet developments are certainly being made. Dr. Richard Kontrimas, CEO of Radian Audio Engineering, which has been in business in Orange, CA since 1988, has leveraged his background in metallurgy to make improvements in aluminum compression driver diaphragms. But more dramatic than that, he says, is the beryllium diaphragm made by Materion, which Radian uses in some of its products.

“Beryllium is able to create better mid frequencies, the sounds that make it so rich. You hear transients that you would never hear with a regular diaphragm, aluminum or otherwise,” he says.

“People want beryllium diaphragms and I can’t deliver them fast enough,” says Kontrimas, who reports that the audiophile market is especially eager for the product, which has been met with effusive praise in reviews and on trade show floors. “In Germany, a pair of speakers that have a pair of our coaxial drivers start at about €75,000.”

“Beryllium diaphragms have a much better stiffness-to-weight ratio, which gives them a higher first bending frequency,” comments Matthew Marcum, senior product design engineer at Eminence in Kentucky, which is celebrating its fiftieth anniversary this year. “That lends it to being particularly useful for high frequency devices when you are trying to reproduce out to 20 kHz or even 30 kHz. The downside is that beryllium materials are very hard to produce and work with, so it ends up being a high consumer cost.”

New 1.4-inch and 2-in. exit neodymium drivers from Eminence offer a lower cost alternative via its Damped Diametric Drive technology. “We were able to apply a certain pattern of a carefully selected adhesive that helps connect the surround to the titanium a little more efficiently. While allowing the voice coil to transfer energy to the dome more efficiently, it also acts as a very nice damping mechanism, taking away those spurious resonances that often plague the more affordable diaphragm materials,” Marcum explains.

Other driver manufacturers are producing titanium domes with nitrogen or magnesium coating, he adds. “There are lots of interesting little tricks that are being played now that try and get the best bang for a buck out of a diaphragm.” But, he also notes, “There’s an extra process, extra potential for health hazards—and more cost.”

Although confidentiality agreements typically dictate that speaker manufacturers are unable to name their OEM customers, that market can represent a sizeable chunk of business. For Eminence, as an example, “OEM business is probably between 60 and 75 percent of our business,” Marcum reports.

Radian Audio is also a major player in the OEM component business, sometimes supplying major customers, rather than manufacturers, on that basis. Event services provider PRG in Germany has had a problem with failing diaphragms in certain of its arrays, of which it has over 1,000, reports Kontrimas. But the diaphragm is an unusual size. “So we made a deal to replace the whole driver, not just the diaphragm. [The customer] says the product sounds so much better with our compression driver.”

Single point source coaxial devices are enjoying something of a revival, apparently. “You’ll find our FTX models popping up all over the place,” says Weller. “It takes up less room, potentially, on the baffle, depending on how you want to use it.”

In the MI and custom speaker markets, he continues, “They were always a hard sell, but now people have really bought into the idea of coax units.”

Another buoyant market is the mini line array. “I think there was a time when commentators in our business thought line arrays were a passing fad, but line array products have become a big part of the market. You’ve only got to look around the world at boxes that have coax units in them, employed in a clever way, and there’s a good chance that it’s one of ours,” says Weller.

“You tend to see our AN drivers popping up in little stick arrays. People are using those compact drivers in clever ways to get the throw and the dispersion pattern that they want to cover the audience and not take up as much space.”

“Over the last five to 10 years, line arrays almost all but eliminated point source applications,” Marcum agrees. “But it seems that people are starting to embrace the phase response and the ease of usability in regards to point source applications.”

Celestion has a new product, Axi-Periodic, that was previewed in a 2015 AES paper and debuted at the recent Frankfurt Musikmesse. “It’s a single driver of the compression variety, but it does 300 Hz to 20k without a crossover,” says Weller, noting that the performance comes from the use of certain added materials and a shape that creates the necessary rigidity.

Other companies make similar products but they tend to be two drivers in one concentric product with a crossover network, he continues. “The crossover network is always in the wrong place, the 1 kHz region, where your ear is really sensitive. This is the Holy Grail, if you like, of drive units—a single driver that covers a good chunk of the frequency range without a crossover network.”

“This has never been done before; it’s truly groundbreaking,” adds Cork.

When neodymium magnets became available, says Marcum, “The trend was to get the most bang for the buck and have the smallest, lightest package that you could. What we see more now is people using neodymium for performance, not so much for the weight advantage.”

For example, “A four-or five-inch neodymium slug in there would take maybe 50 or 60 pounds of ceramic to be equivalent to this little 10-pound motor. The motor force that it allows you to create nowadays is unfathomable. It offers so much more flux density compared to ceramics.”

Eminence is collaborating with academics on a quantum leap in magnetic materials, Marcum also reveals. “These will be magnets made from material that use little or no rare earth elements. The cost to produce these magnets is going to be dramatically cheaper.” A product is still some years away, he says, “But the thing that is really going to revolutionize the speaker industry is when a new magnetic material comes out.”