Coaxial designs offer the advantages of a single point source for a consistent acoustic center and a symmetrical dispersion pattern. But designing coaxial systems without acoustic anomalies has been extremely expensive—until now.
Solving the problems involved in coaxial designs requires massive amounts of DSP and subtle, sophisticated transducer design, which is why such systems have, in the past, been limited to very high-end systems with external processors.
However, Fulcrum Acoustic’s amazing, cutting-edge technology has allowed us to overcome the usual design problems of coaxial systems while taking advantage of coaxial’s unique properties. Thanks to custom transducers and TQ algorithms designed by Fulcrum’s Dave Gunness, Sceptre CoActual monitors deliver clarity and coherence that has previously only been available in ultra-high-end systems.
Multi-way, non-coaxial speaker designs have long been the way to go in speaker applications. But they suffer from the changing relationship between the listener and the speaker elements: When you move around in the coverage area, the sound is inconsistent. Even more troublesome, the crossover point between the drivers can sometimes be audible.
Coaxial systems solve this by having the drivers on the same axis, thus providing a single point source for a consistent acoustic center. This results in symmetry of response on both the horizontal and vertical axis, at any given angle. The crossover transition is seamless (inaudible) at all angles. (By “symmetry,” we mean that whatever response is observed at a given angle with respect to the axis, the same response will be observed at that angle in the opposite direction. The loudspeaker’s behavior is “mirrored” about its axis.)
Non-coaxial loudspeakers cannot exhibit this symmetry.
All of which is great for coaxials, in theory—yet very few companies have successfully marketed coaxial studio monitors, and only a few very expensive models are considered to be truly of professional caliber. That’s because coaxial designs are fiendishly difficult to get right. The challenges are complex and, to date, impossible to solve with acoustic design alone. Making it work at high sound-pressure levels is especially difficult.
Fortunately, a company called Fulcrum Acoustic developed a solution based on a sophisticated combination of driver design and signal processing that we’ll discuss in the section “The Magic of TQ™.”
The magic of TQ
No driver is perfect, nor can a driver be made perfect with hardware alone; there are always compromises in physical systems. To overcome these driver compromises, many speaker manufacturers apply DSP in the form of a combination of multiband EQs but the processing is more or less an afterthought—it’s not accounted for in the design of the transducer. This sorta works—more or less.
A few high-end loudspeaker companies have developed sophisticated solutions with active DSP that is co-designed with the speaker, but these are expensive solutions. And only one company has done it with coaxial designs: Fulcrum Acoustic.
So instead of taking the crude, old-skool approach, we partnered with Fulcrum Acoustic and licensed its high-end TQ™ Temporal Equalization, which, up until now, could only be found in very high-end speaker systems.
With TQ, the basic speaker and enclosure designs meet the fundamental physical requirements for accurate, clear sound—characteristics that cannot be obtained with DSP. The TQ algorithms deal with the remaining issues using multiple fully addressable, fairly large Finite Impulse Response (FIR) filters to eliminate horn reflections and to correct linear time and amplitude anomalies. The hardware and TQ settings are designed to work together from the outset, rather than taking an existing speaker system and trying to correct it with DSP.
Sceptre starts out with a transducer that solves many basic coaxial problems through its physical configuration and is also designed so that DSP can be used to correct other issues. In the 8- and 6.25-inch CoActual™ transducer, magnet structures are in close proximity for extremely smooth off-axis response. The purpose-built high-frequency horn contributes to frequency-pattern control and keeps high-frequency energy off of the woofer cone. The woofer’s larger radiating surface works with the HF horn to improve bottom operating-range directional control.
Then Fulcrum’s Temporal EQ™ (TQ) DSP algorithms are applied. It starts with the standard complement of Infinite Impulse Response (IIR) highpass, lowpass, and parametric filters, plus delay. To this is added fully addressable, fairly large Finite Impulse Response (FIR) filters that implement more detailed frequency-response adjustments; and the precise temporal (time domain) filters that are responsible for the most remarkable TQ benefits. As explained in Fulcrum Acoustic’s white paper, “Loudspeakers tuned with TQ provide a crisper stereo image, greater soundstage depth, more separation between the components of a complex mix, increased resistance to feedback, more seamless transitions between distributed loudspeakers, and a less fatiguing listening experience at very high SPLs.”
It seems pretty incredible that a computer—a custom digital signal processor—can eliminate physical horn reflections. But it’s possible when the resonances happen consistently. Knowing in advance how the loudspeaker will respond to a particular signal, it is possible to calculate a special new signal that not only avoids exciting natural resonances, but also actively kills these resonances before they become audible!
Collaborating with Fulcrum Acoustic co-founder, Dave Gunness, PreSonus software designers incorporated custom TQ algorithms into the onboard DSP. The result is a studio monitor with remarkably clear, coherent, detailed sound at a breakthrough price.
These speakers use a nontraditional, asymmetrical crossover scheme and some very tricky time-based processing to increase the output capability and overcome any weaknesses of the drivers.
This scheme has never been implemented before – largely because it is not possible without digital processing, but also because nobody thought of a way to do it, and it takes some pretty crafty phase manipulations to get everything to work.
Sceptres provide extensive user-adjustable contour features that let you optimize the monitors for any listening space.
In addition to making possible the Sceptre’s coaxial design, the monitor’s onboard DSP provides user-adjustable contour features for optimizing the monitors for your listening space. This enables full integration into any environment.
The Acoustic Space Control
A four-position Acoustic Space switch controls a second-order shelving filter centered at 100 Hz, with four attenuation settings (no attenuation, -1.5 dB, -3 dB, and -6 dB) so that you can account for the boundary bass boost that occurs when the monitor is placed near a wall or corner. If you don’t want to roll off those lows, set it to 0 dB.
You also can adjust the Sceptre’s overall sound and response using its performance controls.
The Sceptre’s performance can be customized in several ways.
A sensitivity control that ranges from +4 dBu to -10 dBV helps you match the Sceptres to your mixer’s outputs.
The High-Frequency Driver Adjust switch adjusts the tweeter’s overall level to linear (0 dB), +1 dB, -1.5 dB, or -4 dB. This lets you control the balance between the tweeter’s output and that of the mid/low driver.
The High Pass switch rolls off the low frequencies below the specified frequency (60, 80, or 100 Hz) at a slope of -24 dB/octave. This control is important if you are using a subwoofer in conjunction with the Sceptre S6/S8 monitors; in that case, set it to the same frequency as the crossover to the subwoofer. If you’re not using a subwoofer, you simply set the control to Flat.
Any loudspeaker is subject to an assortment of environmental and performance problems, and Sceptre monitors offer protection from most common of these. RF shielding protects against radio frequencies that could be induced into the signal and become audible.
Sceptre monitors also provide over-temperature protection to avoid heat-related issues and current-output limiting to prevent damage should there be a short circuit on the speaker terminals.
Finally, the power amplifiers have a “soft startup” so that you don’t get damaging pops in the speakers when you power them up.