Xcelsus XUSX6/8 2 WAY SQL X-OVER - Pair

The Xcelsus Philosophy: Engineering Without Compromise

In the world of high-performance car audio, where compromises are often disguised as "design choices" and marketing rhetoric frequently overshadows engineering substance, Xcelsus has always stood apart. Founded by Dawid Koniarski—a Polish-born engineer who built his reputation on the uncompromising principle that authentic sound quality demands authentic engineering—Xcelsus represents a philosophy that refuses to take shortcuts. Every component, every solder joint, every design decision in an Xcelsus product exists because physics demanded it, not because marketing suggested it.

The XUSX68 Ultra SQL passive crossover network embodies this philosophy in its purest form. This isn't a crossover designed to meet a price point or to complement a marketing campaign. It's a crossover designed to solve the fundamental challenges of passive frequency division with the same attention to detail that characterizes professional studio monitor design. When Koniarski and his engineering team set out to create the Ultra SQL series—the company's premium Sound Quality League lineup—they understood that the crossover network would be the critical bottleneck determining whether the system would achieve reference-grade performance or merely acceptable sound.

The result is the XUSX68: a 2-way passive crossover that incorporates Xcelsus's proprietary Phase Shift Technology, employs only premium MXP capacitors and 100% copper air-core inductors, and provides the adjustability necessary to optimize performance with both 6.5" and 8" driver configurations. This is a crossover network designed for enthusiasts who understand that the passive components between your amplifier and your drivers are just as critical as the drivers themselves—and who refuse to accept anything less than the best.

NOS Condition: Understanding New Old Stock Premium Components

New Old Stock Definition: NOS components are products that were manufactured years ago but have never been installed, never been used in a system, and have remained in their original factory packaging. These are not refurbished products, not demo units, not open-box returns. They are genuinely new—manufactured to original specifications, inspected at the factory, and sealed in their original packaging—but they come from discontinued production runs that are no longer manufactured.

Why NOS Matters for the XUSX68: Xcelsus has discontinued the Ultra SQL series, which means the XUSX68 crossover is no longer in active production. For enthusiasts building or upgrading Ultra SQL systems, NOS components represent the only opportunity to acquire genuine factory-produced crossover networks with the exact component specifications and Phase Shift Technology that Dawid Koniarski's engineering team originally designed. These are not "updated" versions with cost-reduced components or "improved" designs that sacrifice the original engineering philosophy—these are the authentic Xcelsus crossovers as originally conceived.

What You're Actually Receiving

Packaging Condition: Because these crossovers have been in storage since their original manufacture, the external packaging may show minor signs of age. This might include slight shelf wear, minor corner creasing, or small surface marks on the box from warehouse storage. The packaging protects the crossover—it's not the product itself—and these cosmetic considerations are typical of NOS components from discontinued production runs.

Product Condition: The XUSX68 crossover itself has never been installed in a vehicle, never been connected to an amplifier or drivers, never been mounted or modified. All factory seals remain intact. All components—MXP capacitors, copper air-core inductors, circuit board, terminals, jumper settings, phase shift switch—are in factory-fresh condition exactly as they left Xcelsus's production facility. The crossover has never been subjected to electrical stress, thermal cycling, vibration, or any of the environmental factors that affect used components.

Testing and Verification: Before offering any NOS component, Audio Intensity conducts thorough inspection to verify authenticity and condition. We confirm that all factory markings match Xcelsus specifications, all component values are correct, all solder joints are factory-original, and no evidence of installation or use exists. This isn't a quick visual check—we verify that you're receiving a genuine Xcelsus product in genuinely new condition.

The NOS Value Proposition

Collector and Enthusiast Value: For owners of Xcelsus Ultra SQL systems, NOS crossovers represent irreplaceable components. When you're building a system around XUSM6 or XUSM8 midranges and XUST30W tweeters, the XUSX68 crossover was specifically engineered to complement those drivers. Alternative crossovers—even high-quality units from other manufacturers—weren't designed with the Ultra SQL series acoustic characteristics in mind, meaning you'd be compromising the system performance that drew you to Xcelsus in the first place.

Original Component Specifications: NOS components guarantee you're receiving the exact MXP capacitors, copper air-core inductors, and circuit board design that Xcelsus specified. As discontinued products age, some sellers attempt to substitute "equivalent" components to reduce costs or address supply chain limitations. With NOS products from Audio Intensity, you're guaranteed original factory components with no substitutions, no modifications, no "improvements" that alter the original engineering intent.

No Manufacturer Warranty: Because Xcelsus has discontinued the Ultra SQL series, factory warranty support is no longer available for these crossovers. However, Audio Intensity stands behind every NOS component we sell with our own warranty coverage and technical support. If you encounter any issues with manufacturing defects or component failure—extraordinarily rare with passive crossover networks—we'll work with you to ensure a satisfactory resolution. We don't sell products and disappear; we're committed to long-term customer relationships.

Phase Shift Technology: Acoustic Coherence Through Electrical Compensation

Understanding the XUSX68's most sophisticated feature—Xcelsus's proprietary Phase Shift Technology—requires understanding the fundamental challenge that passive crossover networks face: acoustic phase shift is an unavoidable consequence of frequency-dependent filtering. When you divide an audio signal into separate frequency bands and route those bands to different drivers, you're introducing electrical phase shifts that translate into acoustic time delays. In practical terms, this means the tweeter and midrange aren't reproducing their respective frequencies at exactly the same moment in time, creating acoustic interference patterns in the crossover region that degrade imaging precision and tonal accuracy.

Most crossover designers accept this phase shift as an unavoidable trade-off inherent to passive filtering. Some attempt to minimize it through careful crossover point selection or by using gentler filter slopes (which reduces phase shift but increases the frequency overlap between drivers, creating different problems). A few manufacturers attempt to compensate for phase shift through physical driver positioning—angling the tweeter or recessing the midrange to create mechanical time alignment—but this approach only works for a single listening position and can introduce diffraction issues.

Xcelsus took a different approach with Phase Shift Technology: electrical phase compensation integrated directly into the crossover network. The XUSX68 incorporates a selectable phase shift circuit that allows you to electrically invert the tweeter's phase relationship relative to the midrange, effectively compensating for the acoustic phase shift introduced by the crossover's filter slopes. This isn't a simple polarity switch that inverts the entire signal—it's a frequency-dependent phase adjustment that specifically targets the crossover region where phase coherence matters most.

Why Phase Matters: The Acoustic Consequences

Crossover Region Interference: In the octave surrounding the 2800Hz crossover point (roughly 1400Hz to 5600Hz), both the midrange and tweeter are reproducing overlapping frequencies. If these drivers are acoustically out of phase, their outputs can partially cancel each other, creating a frequency response notch in the critical presence region where vocal intelligibility and instrument definition reside. This manifests as reduced clarity, diminished detail, and a sense that the music is coming from the speakers rather than from a coherent soundstage beyond them.

Imaging Precision: Accurate stereo imaging requires that identical signals arriving at your left and right ears maintain precise phase relationships. When the tweeter and midrange are acoustically out of phase in the crossover region, the apparent source location of instruments and voices in that frequency range becomes ambiguous. Instead of a precisely defined center image or a clearly positioned off-center instrument, you hear a diffuse, poorly focused sound. Professional studio engineers describe this as "smeared" imaging—you can tell approximately where sounds should be, but you can't point to them with precision.

Transient Response: Musical transients—the initial attack of a snare drum, the pluck of a guitar string, the consonants in a singer's voice—contain energy across a wide frequency spectrum. When the midrange and tweeter are reproducing different parts of that transient with different phase relationships, the transient's acoustic shape is distorted. The result is reduced impact, diminished detail, and a sense that the system is slow or sluggish even though frequency response measurements might look perfect.

The Phase Shift Switch: Optimization for Your Installation

The XUSX68's Phase Shift Technology switch allows you to select between two phase configurations: standard polarity (0°) or inverted polarity (180°). Which setting provides optimal acoustic coherence depends on your specific installation geometry—the physical mounting locations of your midrange and tweeter, the acoustic characteristics of your door panels or kick panels, the distance between drivers, and even the off-axis response characteristics of your specific Ultra SQL components.

Optimization Process: To determine the optimal phase shift setting, play familiar reference tracks with strong center-focused vocal content and clearly defined instrument positioning. Listen with the switch in the standard position, then switch to the inverted position. The optimal setting is the one where:

• Center vocals appear more focused and precisely positioned
• High-frequency detail sounds more integrated with the midrange rather than separated
• Instrument positions within the soundstage have clearer definition
• Transients (drum hits, guitar plucks) have more impact and clarity
• The overall presentation sounds more coherent and less "speaker-like"

There's no "correct" setting that applies to all installations—the optimal configuration depends on your acoustic environment. This is why Xcelsus made the Phase Shift Technology switch easily accessible rather than burying it inside the crossover enclosure. As you refine your system tuning, you can revisit the phase shift setting to verify that your initial choice remains optimal.

Component Quality: MXP Capacitors and Copper Air-Core Inductors

In passive crossover design, the quality of capacitors and inductors directly determines signal integrity. These aren't decorative components or minor details—they're in the direct signal path between your amplifier and your drivers, meaning every electrical characteristic of these components becomes audible. Inferior capacitors introduce distortion through dielectric absorption and equivalent series resistance (ESR). Inferior inductors create distortion through magnetic saturation and hysteresis. Xcelsus understood that achieving Ultra SQL series performance required component quality that exceeds typical automotive audio standards.

MXP Capacitors: Low-ESR Signal Transparency

The XUSX68 employs MXP (Metallized Polypropylene) film capacitors throughout the signal path—a component choice that prioritizes electrical performance over cost reduction. Unlike electrolytic capacitors commonly found in budget crossover designs, MXP film capacitors exhibit exceptionally low equivalent series resistance (ESR) and negligible dielectric absorption, meaning they pass audio signals with minimal distortion and phase shift.

ESR and Signal Integrity: Equivalent series resistance is the capacitor's internal resistance that appears in series with its ideal capacitance. When audio signals pass through a capacitor with high ESR, that resistance dissipates energy as heat and introduces frequency-dependent voltage drops that color the sound. MXP capacitors exhibit ESR values typically measured in milliohms—orders of magnitude lower than electrolytic alternatives—meaning they introduce negligible resistance into the signal path.

Dielectric Absorption: Some capacitor dielectrics (the insulating material between the capacitor's plates) absorb and slowly release electrical charge, creating a form of memory effect that distorts transient signals. Polypropylene dielectrics exhibit virtually zero dielectric absorption, meaning they respond instantly to signal changes without the smearing or distortion characteristic of inferior dielectric materials. This is why polypropylene capacitors are the standard choice in professional studio monitor crossovers where transient accuracy is paramount.

Temperature Stability: MXP capacitors maintain stable electrical characteristics across the temperature range encountered in automotive installations. From winter cold starts to summer dashboard temperatures, these capacitors maintain consistent capacitance values, ensuring that your crossover point and filter slopes remain stable regardless of thermal conditions. Budget capacitors can shift capacitance by 10-20% or more with temperature changes, effectively changing your system's tuning with the seasons.

100% Copper Air-Core Inductors: Zero Magnetic Saturation

The XUSX68's inductors are wound from pure copper wire in air-core configurations—meaning there's no ferrite or iron core inside the coil. This design choice eliminates magnetic saturation and hysteresis distortion, two phenomena that plague iron-core inductors in high-performance applications.

Magnetic Saturation: Iron-core inductors use ferromagnetic materials to achieve high inductance values in physically small packages. However, ferromagnetic materials have a saturation point—a current level beyond which the magnetic field can't increase proportionally. When an inductor saturates, it effectively stops behaving like an inductor and instead acts like a resistor, creating severe distortion. Air-core inductors can't saturate because air is non-magnetic—there's no magnetic material to reach saturation. This means the XUSX68's inductors maintain linear behavior even during high-power dynamic peaks.

Hysteresis Distortion: Ferromagnetic materials exhibit hysteresis—the magnetic field doesn't perfectly track the applied current but instead lags behind it. This creates a form of magnetic memory that distorts the audio signal. Air-core inductors eliminate hysteresis completely because air exhibits no magnetic memory effects. The result is that the inductor's magnetic field precisely follows the audio signal with no distortion introduced by the core material.

100% Copper Conductors: The XUSX68's inductors are wound from pure copper wire rather than copper-clad aluminum (CCA) or other cost-reduced alternatives. Copper offers lower electrical resistance than aluminum, meaning less signal energy is dissipated as heat in the coil's resistance. This is particularly important in the low-pass filter feeding the midrange driver, where the inductor carries the full current delivered to the driver and any resistance in that inductor directly reduces efficiency and introduces power compression.

The Cost of Component Quality

Why don't all crossovers use MXP capacitors and copper air-core inductors? Cost. A single high-quality MXP capacitor can cost more than an entire budget crossover network, and large-value copper air-core inductors are expensive both in materials and in the precision winding labor required. Xcelsus chose to absorb these costs in the Ultra SQL series because the target customer is the serious enthusiast who understands that component quality directly determines system performance. The XUSX68 represents engineering priorities that place performance above profit margins.

2800Hz Crossover Point: Optimizing Driver Integration

The XUSX68's 2800Hz crossover frequency wasn't arbitrarily selected—it represents careful engineering optimization based on the acoustic characteristics of the Ultra SQL series drivers and the realities of automotive installation environments. Understanding why this crossover point was chosen reveals Xcelsus's depth of consideration for real-world system performance.

Midrange Beaming Prevention

As frequency increases, drivers transition from omnidirectional radiation (where sound radiates equally in all directions) to directional radiation (where sound focuses increasingly on-axis). This transition—called "beaming"—occurs when the wavelength of sound becomes comparable to the driver's radiating diameter. For a 6.5" midrange, significant beaming begins around 2000-2500Hz; for an 8" midrange, beaming starts even lower, around 1500-2000Hz.

When a midrange driver beams, listeners sitting off-axis (which is everyone in a car except possibly the driver) hear reduced high-frequency output from the midrange. By crossing over at 2800Hz—just above the midrange's beaming frequency—the XUSX68 ensures that the critical upper midrange and lower treble frequencies (where vocal clarity and instrument definition reside) are reproduced by the tweeter, which maintains wider dispersion at these frequencies. The result is consistent tonal balance and imaging regardless of seating position.

Tweeter Protection and Power Handling

Tweeters are inherently more fragile than midrange drivers. The XUST30W tweeter, while robust by tweeter standards, has a 30mm voice coil and a lightweight diaphragm optimized for high-frequency reproduction—not for handling the mechanical excursion required to reproduce lower frequencies. Crossing over at 2800Hz with an appropriately steep filter slope (the XUSX68 employs second-order filters, providing 12dB/octave slopes) ensures that the tweeter isn't asked to reproduce frequencies below its safe operating range.

This protection becomes critical during dynamic peaks—the moments when you turn up the volume and the bass hits hard. Even though those bass frequencies are theoretically filtered out by the crossover, real-world crossover filters have finite slopes, meaning some low-frequency energy still reaches the tweeter. A higher crossover point with steep slopes minimizes this risk, allowing you to enjoy high output levels without risking tweeter damage from over-excursion.

Acoustic Integration in Automotive Environments

In home audio, speakers are typically positioned at ear level with the tweeter and midrange vertically aligned. In automotive installations, drivers are often mounted in doors (below ear level) or kick panels (significantly below and forward of ear level), and tweeters are typically mounted in sail panels, A-pillars, or dash corners (closer to ear level). This physical separation creates acoustic path length differences that affect how the midrange and tweeter integrate.

The 2800Hz crossover point provides enough frequency separation between midrange and tweeter that small acoustic path length differences (a few inches) don't create severe acoustic cancellation issues. If the crossover point were lower—say, 1800Hz—then path length differences would represent a larger fraction of the wavelength, creating deeper acoustic interference notches. The 2800Hz crossover point represents a practical compromise that allows for flexible driver positioning while maintaining good acoustic integration.

6.5" / 8" Driver Compatibility: Adjustable Jumper Settings

One of the XUSX68's most practical features is its dual compatibility with both 6.5" and 8" midrange drivers through adjustable jumper settings. This isn't simply a marketing convenience—it represents genuine engineering that optimizes the crossover's electrical characteristics for different driver impedances and frequency responses.

Why Driver Size Matters to Crossover Design

A 6.5" midrange and an 8" midrange aren't simply different sizes of the same driver—they have fundamentally different acoustic characteristics that affect how they interact with a crossover network. The 8" driver has more cone area, which typically means higher sensitivity (more output for the same input power) and extended low-frequency response. The 6.5" driver has less cone area but typically extends to higher frequencies before beaming begins and may have lower moving mass, resulting in better transient response.

These differences mean that if you simply connected both driver sizes to the same crossover network, you'd hear tonal imbalances. The 8" driver might sound too loud relative to the tweeter, or the 6.5" driver might sound too quiet. The frequency response might shift slightly, and the power distribution between midrange and tweeter would be suboptimal. The XUSX68's jumper settings compensate for these differences, optimizing electrical matching for whichever driver size you're using.

Jumper Configuration: Optimizing for XUSM6 or XUSM8

The XUSX68 includes internal jumpers that adjust the crossover's component values and filter characteristics to match either 6.5" or 8" drivers. These aren't arbitrary settings—they're based on the measured impedance curves and frequency response characteristics of the Ultra SQL series XUSM6 (6.5") and XUSM8 (8") midrange drivers.

For 6.5" Drivers (XUSM6): The jumper setting optimizes the crossover for the XUSM6's impedance characteristics and sensitivity. This ensures that the midrange and tweeter outputs are properly balanced and that the 2800Hz crossover point aligns correctly with the XUSM6's frequency response. The component values are adjusted to maintain proper phase relationships and prevent excessive overlap in the crossover region.

For 8" Drivers (XUSM8): The jumper setting adjusts the crossover to compensate for the XUSM8's typically higher sensitivity and different impedance curve. This prevents the midrange from overwhelming the tweeter and ensures that the acoustic integration between drivers remains optimal. The filter characteristics are adjusted to account for the XUSM8's earlier onset of beaming and different off-axis response.

Installation Note: The jumper settings are located inside the XUSX68's enclosure and are set during initial installation. You don't need to adjust them during normal use—they're a one-time configuration based on which Ultra SQL midrange driver you're using in your system. Clear jumper position markings on the circuit board ensure correct configuration.

Why Not Use Separate Crossovers?

Some manufacturers offer separate crossover models for different driver sizes, requiring you to purchase a different crossover if you change drivers. Xcelsus's approach with the XUSX68 provides flexibility for system builders who might start with 6.5" components and later upgrade to 8" drivers, or who might use different driver sizes in different vehicle installations. This flexibility is particularly valuable for professional installers who maintain inventory for multiple vehicle applications.

Adjustable Tweeter Level: Optimizing for Installation Acoustics

Beyond the jumper settings and phase shift switch, the XUSX68 includes adjustable tweeter level attenuation—a critical feature for optimizing system balance in real-world automotive environments where installation acoustics significantly affect perceived tonal balance.

Why Tweeter Level Adjustment Is Necessary

In an ideal installation, the midrange and tweeter would have matched sensitivities, be mounted at equal distances from the listening position, and operate in identical acoustic environments. In automotive reality, none of these conditions exist. Tweeters are typically mounted closer to the listener's ears than midrange drivers (which are usually in doors or kick panels), and they often fire more directly on-axis. These factors make the tweeter acoustically louder than the midrange, creating an excessively bright tonal balance that fatigues listeners and creates an unnatural, harsh presentation.

Rather than trying to fix this with equalization (which affects all frequencies reproduced by the tweeter, not just the overall level), the XUSX68 includes built-in tweeter attenuation that allows you to reduce the tweeter's output level to match the midrange. This is accomplished through resistive padding networks that reduce the voltage delivered to the tweeter without introducing reactive components that would alter phase response.

Attenuation Settings and Optimization

The XUSX68 provides multiple tweeter attenuation levels, typically ranging from 0dB (no attenuation) through -3dB, -6dB, and possibly -9dB settings. These levels are selected through internal jumpers that configure resistive padding networks. The optimal setting depends on your specific installation geometry, driver mounting locations, and personal tonal preferences.

Starting Point: Begin with moderate attenuation (-3dB to -6dB) as a starting point, as most installations benefit from some tweeter attenuation due to the tweeter's typically closer mounting distance. Listen to familiar reference tracks with good high-frequency content—cymbals, hi-hats, female vocals, acoustic guitar—and evaluate whether the high frequencies sound natural and integrated with the midrange or excessively bright and forward.

Optimization Process: Increase attenuation if the high frequencies sound harsh, sibilant, or fatiguing—if you find yourself wanting to turn down the volume on bright recordings. Decrease attenuation if the high frequencies sound dull, recessed, or lacking in air and detail—if cymbals sound muted or vocals lack presence. The optimal setting is where high-frequency content sounds natural and effortless, neither demanding attention nor disappearing into the background.

Consider Your Amplifier: If you're using a multichannel amplifier with independent level controls for midrange and tweeter channels, you might achieve similar results through amplifier gain matching rather than crossover attenuation. However, the XUSX68's built-in attenuation provides a convenient optimization method and allows you to use your amplifier's gain controls for other purposes (such as overall system level matching or subwoofer integration).

Passive vs. Active: Why Choose Passive Crossovers

The XUSX68 is a passive crossover network, meaning it operates without electrical power and is inserted between the amplifier and the drivers. In an era where active crossovers (electronic crossovers that divide frequencies before amplification) have become increasingly popular, particularly in high-end installations, the choice of passive crossover design deserves explanation. Xcelsus designed the XUSX68 for enthusiasts who understand that passive crossovers offer specific advantages in certain applications.

Simplicity and Reliability

Passive crossovers contain no active electronics—no operational amplifiers, no power supplies, no digital signal processors. They're purely passive components (capacitors, inductors, resistors) that will function identically for decades without drift, degradation, or failure. There's no firmware to become obsolete, no electronics to fail, no power supplies to create noise. Install the XUSX68 correctly, and it will perform identically twenty years from now as it does today.

This reliability is particularly valuable in automotive applications where temperature extremes, vibration, and electrical noise create challenging operating conditions. Active electronics can fail or degrade over time; passive components rated for automotive environments (as the XUSX68's components are) essentially last forever. For enthusiasts who view their audio systems as long-term investments rather than disposable electronics, this permanence has genuine value.

Simplicity of Installation

Passive crossover installations require no additional power wiring, no signal routing complexity, no concerns about ground loops or electrical noise. Connect your amplifier's outputs to the XUSX68's inputs, connect the XUSX68's outputs to your drivers, configure the jumpers for your driver size, set the tweeter level, and you're done. There's no learning curve for complex DSP software, no need to understand digital signal processing theory, no opportunities to misconfigure parameters that degrade sound quality.

This simplicity appeals to enthusiasts who want to focus on the music rather than becoming audio engineers. Not everyone wants to spend hours learning crossover theory and experimenting with filter slopes, phase adjustments, and time alignment. The XUSX68 embodies decades of Xcelsus's engineering experience in a package that works correctly with appropriate configuration of clearly documented settings.

Pure Signal Path

Passive crossovers process the audio signal purely through reactive components (capacitors and inductors) that store and release energy without generating distortion. There are no analog-to-digital conversions, no digital-to-analog conversions, no operational amplifiers in the signal path. While modern active crossovers can achieve very low distortion specifications, they still introduce some level of electronic processing artifacts—however minimal—into the signal path.

For purist enthusiasts who believe that the best signal processing is no signal processing, passive crossovers represent the most direct path between amplifier and driver. The XUSX68's high-quality MXP capacitors and copper air-core inductors introduce minimal signal degradation—arguably less than the multiple conversion stages in even high-quality active crossovers.

When Active Crossovers Make Sense

To be clear, active crossovers offer genuine advantages in certain applications. They allow for precise filter slope control, individual channel equalization, time alignment compensation, and the ability to use lower-powered amplifiers more efficiently. In professional sound quality competition where every tenth of a decibel matters in measured performance, active systems with DSP processing often dominate.

However, for enthusiasts building Ultra SQL systems for personal enjoyment rather than competition, the XUSX68 passive crossover offers an elegant solution that combines engineering sophistication with practical simplicity. It's designed to work correctly with minimal complexity, allowing you to focus on enjoying music rather than endlessly tweaking parameters.

Technical Specifications

Installation and Integration Guidelines

Optimal Crossover Placement

The XUSX68 should be mounted in a location that minimizes speaker wire runs while protecting the crossover from moisture, extreme temperatures, and physical damage. Passive crossovers can be mounted near the drivers (to minimize wire runs between crossover and drivers) or near the amplifier (to minimize wire runs between amplifier and crossover)—the choice depends on your specific installation constraints.

Near-Driver Mounting: Mounting the XUSX68 near the drivers (typically inside the door cavity near the midrange) minimizes the wire lengths between crossover and drivers, which reduces high-frequency losses in the tweeter circuit and minimizes electromagnetic interference pickup. However, door cavities can expose the crossover to moisture from window mechanisms and temperature extremes, so ensure proper environmental protection if choosing this location.

Near-Amplifier Mounting: Mounting the XUSX68 near the amplifier (typically in the trunk or under a seat) protects the crossover from environmental stresses and makes it easier to adjust jumper settings during system tuning. However, this requires longer wire runs between crossover and drivers, which can introduce some high-frequency losses. Use high-quality speaker wire (14AWG or larger) to minimize these losses.

Environmental Protection: Regardless of mounting location, protect the XUSX68 from direct moisture exposure. While the crossover's components are robust, sustained moisture exposure can corrode connections and degrade solder joints. Consider mounting the crossover in a sealed enclosure or using protective coatings on terminals if environmental protection is a concern.

Wiring Configuration

Amplifier to Crossover: Connect your amplifier's output terminals to the XUSX68's input terminals. If you're using a multichannel amplifier, you might choose to run the midrange and tweeter from separate amplifier channels (bridging the crossover's input for each driver) or to run both drivers from a single stereo channel. Running separate channels provides more power delivery capability and allows for amplifier-level gain matching; running a single channel simplifies wiring.

Crossover to Drivers: Connect the XUSX68's low-pass outputs to the midrange driver (XUSM6 or XUSM8) and the high-pass outputs to the tweeter (XUST30W). Maintain correct polarity throughout—positive amplifier terminal to positive crossover input, positive crossover output to positive driver terminal. Reversed polarity will create acoustic cancellation issues, particularly in the crossover region.

Wire Gauge Recommendations: Use 14AWG or larger wire for midrange connections (which carry more current) and 16AWG or larger wire for tweeter connections. High-quality copper wire with proper insulation prevents signal losses and ensures reliable connections.

Initial Configuration

Step 1 - Set Driver Size Jumpers: Before connecting the XUSX68, open the enclosure and configure the internal jumpers for either 6.5" (XUSM6) or 8" (XUSM8) drivers according to which midrange you're using. Refer to the jumper position markings on the circuit board—these are clearly labeled and documented in the original Xcelsus documentation (which Audio Intensity can provide with your purchase).

Step 2 - Set Initial Tweeter Level: Start with moderate tweeter attenuation (-3dB or -6dB) as an initial setting. You'll optimize this later during system tuning, but starting with some attenuation prevents excessively bright initial performance while you're still familiarizing yourself with the system's character.

Step 3 - Set Phase Shift Switch: Begin with the phase shift switch in the standard position (0°). After the system is fully broken in and you've become familiar with its tonal character, you'll experiment with the inverted position to determine which provides better acoustic coherence in your specific installation.

System Tuning and Optimization

Break-In Period: Allow 20-40 hours of moderate-level playback before making final tuning decisions. The Ultra SQL drivers' suspensions and voice coil formers will loosen slightly during initial use, subtly affecting frequency response and sensitivity. Make preliminary tuning adjustments, but reserve final optimization until after break-in is complete.

Tweeter Level Optimization: After break-in, revisit the tweeter level setting. Play familiar reference tracks with good high-frequency content and evaluate whether the high frequencies sound natural and well-integrated. Adjust the attenuation up or down by one step, listen for several tracks, and determine whether the change improved or degraded the presentation. The optimal setting is where high frequencies sound effortless and natural rather than recessed or aggressive.

Phase Shift Optimization: Once you've optimized tweeter level, experiment with the phase shift switch. Play tracks with strong center-focused vocal content and clear instrument positioning. Compare the standard and inverted settings, listening for improvements in imaging precision, vocal focus, and overall coherence. The optimal setting is the one where the soundstage sounds more three-dimensional and instruments have clearer spatial definition.

Document Your Settings: Once you've optimized the XUSX68's configuration, document your jumper positions, tweeter level, and phase shift setting. If you later need to remove the crossover for vehicle maintenance or system modifications, you'll be able to restore the optimized configuration quickly.

Building the Complete Ultra SQL System

The XUSX68 crossover was specifically engineered to partner with Xcelsus Ultra SQL series components—the XUSM6 (6.5" midrange), XUSM8 (8" midrange), and XUST30W (30mm waveguide tweeter). While the crossover can technically function with other drivers, its electrical characteristics, crossover frequency, and adjustable settings were optimized based on the measured performance of these specific Ultra SQL components. Building a complete Ultra SQL system ensures that every component was designed to work together as an integrated whole.

Ultra SQL Component Synergy

XUSM6 / XUSM8 Midrange Drivers: These midrange drivers were designed with frequency responses that extend smoothly through the 2800Hz crossover point without anomalies or resonances. Their impedance curves, sensitivity specifications, and power handling capabilities match the XUSX68's electrical design, ensuring optimal power distribution and tonal balance. The jumper settings in the XUSX68 specifically compensate for the differences between these two drivers, allowing you to choose driver size based on your installation constraints without compromising system performance.

XUST30W Waveguide Tweeter: This 30mm tweeter incorporates a waveguide (horn loading) that controls directivity and increases sensitivity. The XUSX68's 2800Hz crossover point was selected to match the XUST30W's optimal operating range, ensuring that the tweeter isn't asked to reproduce frequencies below its safe excursion limits. The waveguide design provides controlled dispersion that matches the midrange's off-axis response in the crossover region, creating seamless acoustic integration. The XUSX68's adjustable tweeter level accounts for the XUST30W's higher sensitivity (typical of waveguide tweeters) relative to the midrange drivers.

System Design Philosophy

The Ultra SQL series represents Xcelsus's vision of what a no-compromise Sound Quality League system should be: components engineered to work together as an integrated whole, with each element optimized for its role in the system rather than designed as a standalone product that must work with any partner component. This integrated approach allows for optimizations that aren't possible when mixing components from different manufacturers or different product lines.

The XUSX68's Phase Shift Technology, driver size jumpers, and adjustable tweeter level all reflect this integrated design philosophy. These features were developed based on the specific acoustic characteristics of the Ultra SQL drivers, allowing the system to achieve acoustic performance that would be difficult to match by combining components from different manufacturers—even if those components were individually excellent.

NOS Availability and System Building

Because the Ultra SQL series has been discontinued, building a complete system requires sourcing NOS components from specialized dealers like Audio Intensity. We maintain relationships with distributors and retailers in the domestic market specifically to source discontinued Xcelsus components for enthusiasts building or completing Ultra SQL systems. If you're planning a complete Ultra SQL installation and need to source XUSM6/XUSM8 midranges or XUST30W tweeters to partner with this XUSX68 crossover, contact Audio Intensity—we can often locate NOS components that aren't available through conventional retail channels.

Why Audio Intensity for NOS Xcelsus Components

Discontinued Product Expertise

Audio Intensity specializes in sourcing premium car audio components from discontinued product lines—components that are no longer available through conventional retail channels but that represent engineering and performance standards that are increasingly rare in today's market. The Xcelsus Ultra SQL series exemplifies this philosophy: these components represent engineering decisions that prioritized performance over cost, and they were discontinued not because they were flawed but because the market for uncompromising high-end components is limited.

We maintain relationships with distributors, retailers, and private collectors in the domestic market specifically to source NOS Xcelsus components. When we acquire NOS products, we verify authenticity, inspect condition, and document provenance so you can purchase with confidence. We don't simply resell products—we provide the expertise and verification that make purchasing discontinued components a reliable experience rather than a gamble.

Technical Support and Documentation

Because the XUSX68 is discontinued, manufacturer technical support from Xcelsus is no longer available. Audio Intensity fills this gap by providing technical support, installation guidance, and optimization recommendations for Xcelsus components. We maintain archives of original Xcelsus documentation, installation manuals, and technical specifications that may no longer be available on the manufacturer's website.

If you have questions about jumper configuration, optimal tweeter level settings for your installation, or how to integrate the XUSX68 into a system with specific amplifier or driver configurations, we're available to provide guidance. We view customer relationships as long-term partnerships rather than one-time transactions—when you purchase from Audio Intensity, you're gaining access to our accumulated expertise in premium car audio installation and system optimization.

Authentication and Quality Assurance

The market for discontinued premium components unfortunately includes counterfeit products and misrepresented condition. Audio Intensity's verification process ensures you're receiving genuine Xcelsus products in accurately described condition. We inspect serial numbers, verify component markings, examine solder joints and circuit board quality, and confirm that all specifications match original Xcelsus documentation.

For NOS components, we verify that factory seals remain intact, that packaging is original (not aftermarket replacements), and that no evidence of installation or use exists. This verification process protects you from the risk of purchasing components that were actually used, returned, or refurbished but misrepresented as new.

Our Warranty and Commitment

While manufacturer warranty is no longer available for discontinued Xcelsus products, Audio Intensity provides our own warranty coverage for NOS components. If you receive a XUSX68 crossover that exhibits manufacturing defects or component failure—extraordinarily rare with passive crossover networks, but theoretically possible—we'll work with you to ensure a satisfactory resolution. This might include replacement (if we have additional inventory), repair (if the issue is repairable), or refund depending on the specific circumstances.

Beyond formal warranty coverage, we're committed to ensuring your satisfaction with your purchase and your success in building or upgrading your audio system. If you encounter installation challenges, tuning questions, or integration issues, reach out—we're here to help you achieve the system performance you're pursuing.