Illusion Audio Carbon C10

Overall summary

In this sample and under these test conditions, the Illusion Audio Carbon C10 behaves like a shallow 10 inch subwoofer that is best understood as a compact sealed-enclosure driver, not a high-excursion free-air driver. The 1 volt baseline distortion curve is jagged, with elevated relative THD in the 20 to 40 Hz region and several smaller peaks through the lower midbass. Below ≈25 Hz, higher-order distortion components, particularly H4 and H5, appear more prominent than either H2 or H3, while from ≈30 to 120 Hz, H2 distortion is generally more visible, with H3 distortion coming close in several spots. At 8.5 volts, the distortion shape becomes less broadly jagged through much of the 30 to 90 Hz range, but the low 20 Hz region and the area near 100 Hz remain the most obvious relative distortion features. As with my suspicions about the Illusion Audio C12, it is possible that some of the elevated and jagged distortion behavior seen at the 1 volt level is related to the front-facing motor topology and how it operates at very low drive levels. This cannot be confirmed from the available measurements alone, but the similarity in distortion character between the two models, and my personal experience with the drivers in real world use cases, suggests the motor arrangement may be contributing to the low-level distortion irregularities.

The LSI data explains part of the distortion behavior. The BL curve is the limiting mechanism, with the 70 percent BL point occurring before the CMS 50 percent and Le 17 percent limits. BL is also substantially asymmetrical, with a sharp drop on the outward stroke, and that kind of even-order motor asymmetry is consistent with the H2 distortion contribution seen in the TRF data. The suspension side is much better behaved, with CMS staying beyond the 50 percent limit in the measured window and showing very good symmetry. Le(x) varies with position, but the Le 17 percent criterion is not reached inside the protection window, and Le(i) is stable.

For sealed use, the enclosure data is straightforward. The manufacturer’s 0.75 ft³ sealed recommendation nets a Qtc of 0.717 on this sample, while 0.78 ft³ nets a 0.707 Qtc. That is a very small difference in practical box size, so the published sealed recommendation is close to the measured 0.707 target.

Manufacturer's suggested use case

The manufacturer positions the Carbon C10 as a shallow-mount 10 inch subwoofer intended for installations where mounting depth is limited and enclosure volume needs to remain relatively compact. The published 75.6 mm mounting depth, moderate 0.75 ft³ sealed enclosure recommendation, and emphasis on a sealed alignment suggest a design aimed at space-constrained vehicle applications such as under-floor installations, shallow side-panel enclosures, compact trunk systems, and other locations where a conventional deep-mount subwoofer may not fit. Published specifications include a woven carbon fiber cone, rubber surround, cast aluminum basket, 51 mm voice coil, 300 watts nominal power handling, 600 watts maximum power handling, 10 mm Xmax, and a recommended 0.75 ft³ sealed enclosure with 50 percent fill using Black Hole Stuff.

Our suggested use case

Based on the data, this sample lines up with what the manufacturers goal seemingly was, and makes the most sense in compact sealed enclosures where shallow mounting depth matters and where the enclosure provides mechanical support at low frequencies. The manufacturer’s 0.75 ft³ recommendation is very close to the measured 0.707 Qtc target, so there is no major enclosure-size conflict for normal sealed use. Infinite baffle is not recommended because this sample’s Qts and BL-limited clean stroke do not leave much margin once the sealed air spring is removed.

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: 8.5 volts volts

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

Rated power (published): 300 watts

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ≈6.7 percent of the rated power was used for the high level free-air TRF sweep. At that level, this sample reached 6.8 mm one way at 20 Hz in free air, below the 8.72 mm BL 70 percent point.

Claimed Xmax vs. measured at BL 70%: 8.72 mm one way at BL 70 percent, 87.2 percent of the manufacturer’s 10 mm claim.

Xmax @ 50% Cms: >10.09 mm one way, greater than 100.9 percent of the manufacturer’s 10 mm claim.

Xmax @ 17% Le: >10.09 mm one way, greater than 100.9 percent of the manufacturer’s 10 mm claim.

Manufacturer suggested sealed enclosure size (and its resulting QTC): Claimed 0.75 ft³ nets a Qtc of 0.717.

Required sealed enclosure for 0.707 QTC: 0.78 ft³ nets a 0.707 Qtc.

Xmax @ 50% Cms: >10.09 mm one way, greater than 100.9 percent of the manufacturer’s 10 mm claim.

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: Klippel TRF was used for response and harmonics, with the nearfield mic positioned at 1/10th the cone diameter plus 2 inches, on axis. Response was measured to 1 kHz, THD was measured to 500 Hz, and 1/6 octave smoothing was used. Two drive levels were used: 1 volt baseline and 8.5 volts high level, with the high level sweep set under the BL 70 percent rule from LSI for this sample. This sample reached 6.8 mm one way excursion at 20 Hz in free air during the high level sweep.

At 1 volt - baseline

The 1 volt distortion curve is jagged, especially from 20 to roughly 70 Hz. THD is about 4 percent at 20 Hz, with multiple peaks in the 25 to 40 Hz region and another smaller narrow peak around 100 to 110 Hz. Below ≈25 Hz, the higher-order harmonics are more prominent, with H4 and H5 standing out more clearly than the H2/H3 relationship alone would suggest. From ≈30 to 120 Hz, no single harmonic consistently dominates. H2, H3, H4, and H5 all track relatively close to one another, with various narrow peaks appearing in different harmonics across the band. The overall harmonic balance is irregular and changes frequently with frequency rather than being driven primarily by one distortion order. There is also an unusual amount of H4 and H5 harmonic content present compared with many conventional subwoofer designs. While these measurements alone cannot determine the exact cause, my hypothesis is that the front-mounted motor structure may make motor-related operational noise and higher-order distortion products more acoustically apparent because the motor is not positioned behind the cone in the same way as a traditional rear-motor design.

At high level voltage (8.5 volts volts)

At 8.5 volts, the relative distortion plot changes shape instead of simply scaling upward from the 1 volt curve. THD is still elevated near 20 Hz, at about 4.5 percent, but much of the 30 to 90 Hz range sits lower than the 1 volt percentage plot. The most obvious higher-frequency feature inside the desired subwoofer passband is the narrow rise around 100 to 110 Hz, where THD again reaches roughly 4.5 percent. Below ≈40 Hz, H3 distortion is the dominant H2/H3 contributor. From ≈40 to 120 Hz, H2 and H3 distortion are generally the same, but an H3 distortion peak pops up around the 100 Hz mark.

Delta - 1 volt distortion vs. high level distortion

Compared with 1 volt, the high level sweep does not show a broad percentage increase through the whole 20 to 120 Hz band. Much of the 30 to 90 Hz range is lower in relative percentage at 8.5 volts, while the low 20 Hz region and the narrow 100 to 110 Hz feature remain the standout areas. This does not mean the driver is producing less absolute distortion energy at the higher level, because the distortion percentage is relative to a much higher fundamental output. The lower-level jaggedness may include low-level operational noise, or other non-harmonic behavior that is more visible at 1 volt. This cannot be confirmed from these measurements alone, but are my suspicions based on my first hand experience with these drivers.

What this means in practice

At the high level sweep, the cleanest measured region is roughly 30 to 90 Hz, while the low 20 Hz range and the narrow 100 to 110 Hz region are the highest relative distortion areas inside the desired subwoofer passband. H3 distortion dominates below ≈25 Hz, while H2 distortion is generally stronger through most of the 30 to 120 Hz band. The practical clean stroke ceiling in this sample is set by BL, while CMS and Le do not cross their project limits within the measured window. One additional observation is that the unusually jagged and somewhat abnormal-looking low-level distortion behavior, which is very similar to what was observed on the larger Carbon C12, suggests there may be some operational noise, motor noise, air noise, or a combination of non-harmonic artifacts contributing to the measurement. The TRF data alone cannot definitively identify the source, but based on both the measured behavior and personal experience with these two drivers, operational or mechanical noise appears to be a plausible explanation for some of the irregular low-level distortion features.

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 occurs at 8.72 mm one way. The BL curve is not a wide, flat plateau; it stays higher on the coil-in side and drops more sharply on the coil-out side. That outward drop is what sets the measured BL-based clean stroke limit for this sample. This behavior is consistent with the test engineer note that BL asymmetry is substantial and drops sharply on the outward stroke.

Bl(x) symmetry

The BL symmetry point is -1.74 mm at xprot, with 33.59 percent BL asymmetry. That is a substantial offset in motor force when looking at it based on percentage over the evaluated stroke. Since BL asymmetry maps to even-order distortion, this is consistent with the visible H2 distortion contribution in the TRF results. This is the main large signal weakness in this sample.

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 was not reached within the 10.09 mm one way protection window. The LSI report lists the CMS limit as >10.09 mm one way, which is favorable relative to the published 10 mm Xmax claim. The supplied CMS curve shows compliance gradually reducing toward both ends of travel rather than collapsing early. The suspension is not the first standardized limit for this sample.

Cms(x) symmetry

CMS symmetry is very good, with stiffness asymmetry listed at 3.04 percent. The attached CMS curve is also visually well centered across the measured range. That means the suspension is not adding the same kind of major directional imbalance that is seen in BL. Any even-order distortion contribution from CMS is likely secondary to the BL asymmetry in this sample.

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 0.83 mH in the large signal cold state. Le(x) changes with position, falling more on the coil-in side than on the coil-out side, but the 17 percent Le criterion is not reached within the 10.09 mm one way protection window. The reported Le limit is >10.09 mm one way. Based on the inductance behavior, there is some positional variation, but Le is not the practical clean stroke limiter for this sample. My assumption based on the measurement and its big brother, the Illusion C12, is that there is no inductance management features such as a shorting ring, in the motor design, BUT the smaller voice coil on the 10" is allowing for better inductance performance over the 12" version.

Current dependence

Le(i) is stable across the measured current range, with very little visible 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

Near center, Qts is 0.37 large signal cold, 0.39 large signal warm, and 0.41 small signal. Qts(x) rises with excursion, but is much more heavily biased toward the coil-out side. This asymmetry follows the direction where BL falls more sharply, so damping becomes less consistent as the driver moves farther outward. This can contribute to changing control and compression behavior near the upper end of the usable stroke.

LSI takeaway

For this sample, BL is the first standardized limiting mechanism, with BL 70 percent at 8.72 mm one way. The BL curve is offset and falls sharply on the outward stroke. CMS remains beyond the 10.09 mm protection window and is very symmetrical, so the suspension is not the primary large signal limitation. Le(x) shows positional variation, but Le(i) is stable and the Le 17 percent limit is not reached inside the measured window. Qts rises more on the outward stroke, which points to less consistent damping as the driver approaches higher excursion. Interestingly, these large-signal motor limitations do not appear to translate into the TRF data as strongly as might be expected. Despite the motor being the weakest aspect of the driver from a linearity standpoint, harmonic distortion remains relatively low overall, particularly at normal drive levels. Interesting...

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.75 ft³ nets a Qtc of 0.717 on this sample.

Sealed volume required for 0.707 QTC on this sample: 0.78 ft³

Applicable for infinite baffle? Not recommended.

T/S parameters