Illusion Audio C10XL

Overall summary

In this sample and under these test conditions, the 1 volt baseline shows low broadband distortion in the upper-bass range, but a quickly rising and peaky distortion profile at 40hz and under. Even order H2 distortion is the main contributor in the lowest octave, with a major spike centered around 28Hz, and a major H3 peak in distortion at about 20Hz. At the near limit sweep of 25 volts, distortion increases broadly rather than in sharp peaks; H3 distortion remains dominant at the extreme low end while H2 distortion takes over above 25Hz. Distortion at higher drive is relatively well behaved, but a bit elevated on the low end. Overall, pretty good for a 10” from what we have seen in this test.

The large signal data show a BL 70 percent one way limit of 17.04 mm with varying symmetry across stroke, a CMS 50 percent point not reached within the ±17.31 mm window with good symmetry, and an inductance variance limit of 17% at 12.66 mm. Le(x) varies moderately with position while Le(i) is comparatively stable with current. This combination of varying inductance and BL asymmetry aligns with the measured pattern of low band H3 distortion and a growing H2 distortion component as drive increases.

For sealed enclosure use, the published 0.75 ft³ recommendation computes on this sample to about 0.8 Qtc, which is acceptable for most car audio installations. Reaching approximately 0.707 Qtc requires a slightly larger volume of 1.18 ft³. Practical clean one way stroke is set first by the Le variance over stroke based limit rather than BL or CMS, so planning around that ceiling or using multiples is the straightforward way to raise clean headroom.

Overall, for a 10” subwoofer, this isn’t a terrible performer so long as you don’t ask much of it out of the lowest frequencies.

Manufacturer's suggested use case

The manufacturer doesn’t provide much information, most likely because it has been discontinued for some time now. Highlights include a woven carbon fiber laminated cellulose cone, a cast aluminum basket, and a dual 2 + 2 ohm voice coil system, and the intention of sealed enclosure use. The spec sheet lists 500 watt nominal power, a recommended 0.75 ft³ sealed enclosure with 50 percent fill, 18 mm one way xmax, and 86 dB sensitivity at 2.83 V/1 m.

Our suggested use case

Based on this sample in these test conditions, small-medium sized sealed enclosures are the straightforward path. The manufacturer’s 0.75 ft³ size yields about 0.8 Qtc here, which is a usable end result in automotive applications and is compact and easy to fit. A larger sealed volume lowers Qtc to the ideal 0.707 and increases low frequency sensitivity, but this obviously does not change the inductance based clean stroke ceiling. If very low frequency content will be played at higher levels, consider multiple drivers to remain within the clean region defined by the Le limit. This would also be a decent front-subwoofer filling in between a larger rear sub and front midbass drivers if you can accommodate its depth.

Testing and linearity limits vs. what is advertised

What it took to reach our high-level sweep limit, and how that compares to the published specs.

High-level sweep rule: Set just under the BL 70 percent point from LSI

High-level sweep limit for this sample: 25 volts

Approximate electrical power at that limit at 20Hz: ~150 watts. Real power varies with frequency and impedance. volts

Rated power (published): 500 watts

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ≈30 percent. Hits 17 mm 70 percent BL xmax in free air with 150 watts of power.

Claimed Xmax vs. measured at BL 70%: 17.04 mm, ≈94.7 percent of the manufacturer claim of 18 mm.

Xmax @ 50% Cms: > 17.31 mm, at least 96.2 percent of the manufacturer claim of 18 mm within the evaluation window.

Xmax @ 17% Le: 12.66 mm, ≈70.3 percent of the manufacturer claim of 18 mm.

Manufacturer suggested sealed enclosure size (and its resulting QTC): 0.75 ft³ sealed which nets a Qtc of ≈ 0.8 on this sample.

Required sealed enclosure for 0.707 QTC: 1.18 ft³

Xmax @ 50% Cms: > 17.31 mm, at least 96.2 percent of the manufacturer claim of 18 mm within the evaluation window.

Overall performance snapshot

This is our subjective interpretation of the objective data. How we derive these scores can be found on the home page of the testing section.

Distortion & frequency response - TRF measurements

Method recap: Nearfield mic positioned at one tenth the cone diameter plus 2 inches, on axis. Response measured to 1 kHz and THD to 500 Hz. 1/6 octave smoothing. Two drive levels, 1 volt baseline and a high level at 25 volts set under the BL 70 percent rule for this unit. In this sample at that drive level the unit reached about 17 mm at 20 Hz in free air. Distortion is reported both as percent and by harmonic.

At 1 volt - baseline

Distortion trends upward into the lowest octave with H2 distortion mostly dominant around 20 to 30 Hz, with a 28hz H2 peak hitting nearly 6%, and also a 20hz peak of H3 distortion exceeding the 10% window of the graph. Above roughly 40 Hz broadband THD falls to low er, more acceptable levels and remains relatively smooth.

At high level voltage (25 volts)

Distortion rises broadly as excursion increases. H2 distortion remains the main contributor across the board, while H3 distortion becomes more pronounced in the 25Hz and lower area. The increase presents as a relatively gradual and linear rise as frequency drops rather than sharp spikes, consistent with the LSI behavior exhibited on this driver.

Delta - 1 volt distortion vs. high level distortion

From baseline to high level, magnitude increases most in the 20 to 40 Hz band, with the distortion response turning smooth and broad, and is dominated mostly by even order components across the entire intended frequency range, except with H3 distortion becoming dominant below 25Hz. Operation was set just under the BL 70 percent point and below the CMS 50 percent point; the earlier 17 percent Le based limit most likely explains the rise in odd order content as level increases into the mid band.

What this means in practice

Expect clean output above the lowest frequencies at moderate levels, with distortion rising as content extends toward 20 to 30 Hz, and as excursion increases. The inductance based limit at 12.66 mm one way is the practical ceiling before the BL or CMS thresholds on this sample, so very low frequency material at high level will enter higher distortion quickly. Using multiple of these subwoofers is the best way to remain in the clean operating region if you also want to achieve realistic levels of output and with accurate, low distortion reproduction.

Motor & suspension linearity - LSI measurements

Method recap: Klippel LSI large-signal identification for this unit, cold and used for enclosure computations. Standard thresholds in this project are BL 70 percent, CMS 50 percent, and a 17 percent inductance variance criterion. Commentary below ties the large-signal behavior to the acoustic results.

Bl(x)

Bl(x) shows how much motor force a speaker produces as the voice coil moves, B is magnetic field strength and L is the wire length in that field. A high, wide, symmetrical BL curve means linear control and low distortion, a steep or uneven drop means earlier output limits and rising distortion, which is why BL(x) is often the most telling single Klippel LSI indicator of real performance.

Bl(x) window and shape

BL 70 percent is 15.52 mm one way. The BL curve shows a reasonably broad shelf with an off-center peak, sustaining motor force over most of the stroke. The shape is not as flat nor symmetrical as it should be.

Bl(x) symmetry

The BL symmetry point is ≈ −1.63 mm at full excursion, but is approximately 4mm off center at low excursion and is showing a moderate inward bias. This is consistent with the increased H2 distortion observed across the entire bandwidth.

Cms(x)

Cms(x) is suspension compliance versus displacement, the inverse of stiffness. When the curve is broad and symmetrical, motion is linear and distortion stays low. Early roll off or offset indicates progressive stiffening or mis-centering, which adds mechanical distortion and caps clean excursion.

Cms(x) window and shape

CMS 50 percent is not reached within the ±16.07 mm window, which is favorable for suspension headroom. The suspension maintains usable compliance across the tested range.

Cms(x) symmetry

Suspension asymmetry is somewhat extreme, and is approximately 2.5mm off center at full excursion, but as far off center as 9mm at low excursion. This also aligns with even order distortion levels present in the TRF data.

Inductance - Le(x) and Le(i)

Le(x) and Le(i) measure how a subwoofer’s voice coil inductance changes with position and current. These curves show how stable the motor’s magnetic field is under real movement and drive conditions. When inductance varies heavily, it causes distortion, uneven response, and a loss of upper-band clarity, which is why Le(x) and Le(i) are critical for evaluating how clean and consistent a motor’s behavior really is.

Level and shape

Le at rest is 2.24 mH. The 17 percent Le variance threshold occurs at 6.75 mm one way excursion, earlier than BL or CMS, making inductance the earliest practical clean limit. Le(x) variation is moderate to strong and aligns with the H3 distortion behavior at the bottom.

Current dependence

Le(i) shows moderate current dependence.

Qts(x)

Qts(x) is the driver’s total damping versus excursion, combining electrical and mechanical losses. Stable, symmetrical Qts(x) means consistent control, while large variation or asymmetry signals uneven damping that can shift response, raise distortion, and cause compression.

Qts stability

Qts at center is 0.57 cold, rising with both stroke and temperature. QTS across stroke is very asymmetrical due to the asymmetries listed above. Control decreases outward, aligning with the rise in distortion at higher excursion.

LSI takeaway

On this sample the earliest limit is inductance, with the 17 percent Le variance limit reached at 6.75 mm one way excursion, so Le sets the practical clean stroke ceiling. Both BL and CMS show large low-excursion asymmetries, which align with the strong H2 distortion across the band. The BL curve is off centered with a non-flat peak, and CMS is heavily shifted, especially at small stroke, so even-order distortion is expected to stay high as level rises. Inductance varies strongly with position and shows early departure from linearity, which matches the dominant H3 distortion below about 25 Hz. Qts rises with stroke and is also very asymmetric, indicating weakening control at higher drive, which helps explain the broad distortion growth at real-world playback levels.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.8 ft³ sealed nets a Qtc of 0.79 on this sample.

Sealed volume required for 0.707 QTC on this sample: 1.49 ft³.

Applicable for infinite baffle? Conditionally workable; with Qts ≈0.57 and 1.49 ft³ required for 0.707 Qtc, it can function in infinite baffle if output expectations are kept in check, but the driver is clearly optimized for average sized sealed use.

T/S parameters