Blogging on Audio
- Written by Jeff Fritz Jeff Fritz
- Parent Category: BloggingOnAudio BloggingOnAudio
- Created: 21 September 2021 21 September 2021
In my May 1, 2021, SoundStage! Ultra article, “What Matters Most in an Audio System: The Loudspeaker Drive Unit,” I interviewed Vivid Audio’s technical director, Laurence Dickie, one of the world’s preeminent loudspeaker designers. The interview was all about drivers, obviously, and their importance above all other single factors in the design of a finished loudspeaker. In that article, Dickie—whose Vivid loudspeakers such as the Giya series are legendary in the industry—said something important:
I think we all share the understanding that the ideal speaker driver would convert the electrical voltage signal delivered by the amplifier into an exact air-pressure analog. Sadly, the reality never quite hits the target, and even the first process, the transduction between voltage and force, is subject to a host of nonlinearities that will introduce frequencies not present in the original signal, some inoffensive and even quite consonant, but others dissonant and harsh.
If we’ve established from Dickie’s statement that the drive unit is paramount in a full-range loudspeaker, would that change if the discussion were about subwoofers? Nope.
Since it’s football season, let’s think about the subject with a gridiron analogy: if a tweeter is a graceful wide receiver, capable of athletic feats that require speed and finesse, then a subwoofer driver is clearly an offensive lineman, tasked with moving things that don’t want to move, over and over again. Brute force and explosive power are required characteristics. Add to that list durability and agility.
The SVS SB16-Ultra subwoofer is the flagship sealed-box subwoofer in the company’s line. In it is SVS’s best subwoofer driver, the 16-Ultra-series 16″ woofer. For the entire scoop on this beast of a sub driver, I interviewed Smith Freeman, senior director of product management at SVS.
Jeff Fritz: Why did SVS choose to develop the 16-Ultra-series driver, and what were the initial design goals?
Smith Freeman: When we were designing the biggest and most formidable driver ever used in an SVS subwoofer, it was of utmost importance to push the boundaries of what is possible in terms of control and accuracy. Larger-driver subwoofers are adept at moving massive amounts of air, plumbing infrasonic frequencies, and creating heart-pounding sound pressure levels, but where they sometimes struggle is with speed in transients and the ability to faithfully render bass notes as the artist intended. The pluck of a bass guitar string or the snap of a tympani drum, for instance.
Ultimately, this was a completely new design direction for SVS from the ground up. We knew how many larger-driver subwoofers performed, and the shortcomings we had to overcome. We spent over a year in development, which led us to a 16″ driver married to an 8″ voice coil and an all-new motor design that exhibited all the hallmarks of an SVS subwoofer with chest-thumping output and subterranean extension without compromising on accuracy and transient speed like many other larger-driver subwoofers.
JF: Was it a goal from the outset to use it in both sealed and ported versions of the ultimate SVS subwoofer? Did the dual applications mean you had to accomplish anything different in the design phase?
SF: Yes, we knew we wanted the drivers to be the same size, but the physical design of the sealed-cabinet SB16-Ultra differs from the ported-cabinet PB16-Ultra. In the ported model, we use what’s called an underhung motor topology, where the voice coil sits completely in a high magnetic gap over the entire excursion range of the driver.
Conversely, the SB16-Ultra uses an overhung motor topology, where the voice coil height extends above and below a shorter magnetic gap, preserving the same amount of the voice coil in the magnetic gap over the entire excursion. This motor architecture is optimized for smaller sealed cabinets as opposed to its underhung sibling.
Both of these designs are optimized for their application since both designs allow for extremely linear motor force over the full excursion range of the driver with incredibly low distortion within the cabinet geometry and the complete subwoofer ecosystem.
JF: Why an 8″ voice coil? Is it all about power handling?
SF: This innovation ensures ultra-low distortion, efficient heat dissipation, exceptional linearity and pistonic motion, and nearly zero power compression. By nature, larger drivers are more difficult to control, but the voice-coil design ensures accuracy in frequency response and precise speed in transients without ever sounding boomy. It also eliminates dynamic cone deflection at extreme excursion levels.
While the size of the voice coil is certainly a highlight, there are other design features that warrant mentioning. The 16-Ultra voice coil employs an edge-wound flat-wire design, which ensures higher coil density (compared to round-wire) for a given length of voice coil and higher field density for greater motor strength and improved driver control. It’s also mechanically stiffer than a round-wire voice coil, so it’s less prone to warping.
The material used is copper-clad aluminum wire because it’s lighter than pure copper for reduced moving mass, higher thermal capacity, and more strength than pure aluminum.
JF: From a manufacturing standpoint, were there any challenges that you had to overcome?
SF: Typically, subwoofer drivers measuring 15″ or larger are suited to deep low-frequency extension and room-shaking output, but they are also very difficult to control and subject to boominess, inaccuracy, and a blurring of bass notes. We worked tirelessly to solve these issues, particularly with the 8″ edge-wound voice coil, to allow the driver to deliver incredible output and low-frequency extension while maintaining accuracy in frequency response and speed in transients.
Of course, a driver is just potential, and it requires an equally capable amplifier to get the best performance possible, which was the other big challenge. For this, we deployed a 1500W RMS, 5000W+ peak design with fully discrete MOSFET output that combines the high-current output of discrete MOSFETs with class-D efficiency and the processing power of a 50MHz Analog Devices DSP, so it has brains to match the brawn.
To ensure the 16-Ultra series can operate on any normal AV outlet, the power supply employs PFC (power factor correction) to ensure the cleanest 1500W output regardless of what is coming out of the wall.
JF: How does the 16″ driver perform in the real world? Has it met SVS’s expectations?
SF: In terms of in-room response and real-world output, we couldn’t be more pleased with the performance of the 16-Ultra-series subwoofers. They have emerged as the reference standard for bass in many home theaters and hi-fi systems, and they remain some of the top-selling SVS models, outperforming much larger subwoofers costing two or three times their price.
Next time we’ll set this baby up in my room.
. . . Jeff Fritz
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