Xcelsus XXS12

Overall summary

In this sample and under these test conditions, usable clean stroke is capped early by inductance, not by BL or CMS. The 17 percent Le criterion occurs at ≈ 7.45 mm one way, while BL-70 sits wider at ≈ 12.20 mm and CMS-50 is beyond the protected window.

Baseline distortion at 1 V reads as elevated in the lowest octave and does not collapse to very low values higher in band. At the standardized 10 V high-level sweep, distortion scales broadly across 20 to 120 Hz rather than appearing as a narrow defect, with even-order terms favored by motor/suspension asymmetry and rising odd-order toward 20 to 30 Hz consistent with Le(x,i).
Large-signal data explains the shape: BL has a usable shelf but is biased toward coil-out, CMS symmetry looks good within the resolved window, and inductance variance with position and current is the practical ceiling.

Best fit is infinite baffle given the very high Qts and the inability to reach a ~0.707 sealed alignment on this sample. Sealed alignments are impractical here because Qts is already so high. Plan on modest excursion targets.

Manufacturer's suggested use case

The manufacturer lists sealed alignments. A dealer cites 500 W RMS. There is no published Xmax. On this sample, their stated sealed direction computes to ≈ 0.95 Qtc by claim, which lands at ≈ 1.535 Qtc using our measured parameters. Treat that as very under-damped on this unit and expect a pronounced shape in the low end.

Our suggested use case

Infinite baffle is somewhat viable and with a Qts ≈ 0.98 cold at rest on this sample, it is the only alignment that makes sense. Target conservative levels since inductance variance caps clean stroke around ≈ 7.45 mm one way excursion and BL/CMS asymmetry may be a contributing factor to distortion. If more output is required, add cone area rather than drive one unit hard.

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: 10 volts

Approximate electrical power at that limit at 20Hz: ~50 watts. Real power varies with frequency and impedance. volts

Rated power (published): 500 W RMS (dealer mentioned; nothing on manufacturer page).

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ≈ 10 percent of the 500 W rating.

Claimed Xmax vs. measured at BL 70%: no published claim vs 12.20 mm measured.

Xmax @ 50% CMS: > 13.19 mm one way within protection window.

Xmax @ 17% Le: Practical clean one-way limit is 7.45 mm from Le variation. Percent of claim is not applicable as there is no manufacturer specified xmax.

Manufacturer suggested sealed enclosure size (and its resulting QTC): The manufacturer cites a recommendation of 0.95 cubic feet of airspace. This sample computes to a 1.535 QTC in this airspace.

Required sealed enclosure for 0.707 QTC: A QTC of ~0.707 is not possible due to the already very high Qts of 0.98.

Xmax @ 50% CMS: > 13.19 mm one way within protection 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: Method Recap: Nearfield microphone positioned at 1/10th the cone diameter plus 2 inches, on-axis. Response measured to 1 kHz and THD to 500 Hz, both with 1/6-octave smoothing. One sweep at 1 V baseline, one sweep at a high level set just under the BL-70 point. Coils were D4 in parallel to 2 Ω. Near-limit sweep was 10 V, about 50 W in free air, logging ≈ 9.4 mm one way at 20 Hz.

At 1 volt - baseline

Distortion is elevated in the lowest octave and remains visible well above 40 Hz. There is a peak in distortion at 20 Hz a bit over four percent, dominated by H3 distortion, and a second peak at 28 Hz around five percent, primarily H2 distortion.

At high level voltage (10 volts)

Distortion is high across 20 to 120 Hz, reaching 14 percent at 20 Hz. H3 dominates from 20 to 30 Hz, consistent with Le(x) and Le(i) modulation at higher current. H2 remains elevated at around 5-7 percent through much of the band, best explained by BL(x) asymmetry that favors coil-out and reduces clean headroom on coil-in. Because the sweep remained inside BL 70 percent and CMS 50 percent, the broad elevation is not a hard-stroke artifact; it reflects inductance effects and BL asymmetry rather than a lack of linear stroke.

Delta - 1 volt distortion vs. high level distortion

From 1 V to 10 V the localized 28 Hz H2 peak spreads into wide H2, most likely because the BL(x) bias shifts the operating point off-center with level, so force vs displacement is asymmetric over the whole stroke. Odd-order still grows below ~30 Hz, most likely from high Le(x) and Le(i) variance, but the notable change vs baseline is the broad rise in H2 driven by BL asymmetry.

What this means in practice

Expect audible distortion even at modest drive. H3 from 20 to 30 Hz tracks with inductance modulation at higher current, and the passband-wide H2 rise hints at coming from BL(x) asymmetry that favors coil-out and cuts clean headroom on coil-in. Increasing voltage mainly raises distortion rather than unlocking cleaner output because the sweep stayed inside BL 70 percent and CMS 50 percent.

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 reaches 12.20 mm one way. The shelf is smooth but tilted rather than flat, so force declines steadily across the travel with no sharp knee inside the window.

Bl(x) symmetry

Symmetry point is offset ≈ 2.74 mm toward coil-out, which can explain the high H2 distortion across the board. It also reduces clean headroom on coil-in stroke.

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 not reached within protection; > 13.19 mm one way. No sharp knee in the observed window.

Cms(x) symmetry

Reported as excellent within the resolved window; nothing here counters the coil-out BL bias. CMS only resolved to ≈ 70 percent on 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 ≈ 0.67 mH (large-signal cold). The 17 percent variance limit occurs at ≈ 7.45 mm one way, earlier than BL-70 or CMS-50 and therefore the practical clean-stroke ceiling. This could explain the elevated H3 distortion at lower frequencies.

Current dependence

Inductance modulation with current is present; together with Le(x) possibly explains increased H3 distortion toward 20 to 30 Hz at higher drive.

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 rest is extremely high on this sample (≈ 0.98 cold and over 1 when warm). The trend under stroke and temperature remains high and biased by the BL tilt and Le gradient rather than by CMS, aligning with the sealed alignment impracticality and the IB lean. Regardless, this driver is still too underdamped for most applications where accuracy is valued, even in free air.

LSI takeaway

Inductance variance is the first limiter on this sample, with the 17 percent threshold at ≈ 7.45 mm one way setting the practical clean-stroke ceiling. BL provides a wider window but is tilted and offset ≈ 2.74 mm toward coil-out, which raises H2 distortion and cuts clean headroom on coil-in. CMS does not constrain within the observed window, so the elevated distortion seen at 10 V is not from a hard mechanical stop. Very high Qts keeps damping low, which lets the BL bias and inductance effects show clearly in TRF. In practice, keep excursion modest and use more cone area or multiples if you need additional output, with infinite baffle as the most sensible alignment for this unit.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.95 ft³ claimed; on this sample that alignment computes to a Qtc of 1.535.

Sealed volume required for 0.707 QTC on this sample: Not possible because QTS is already very high on this unit (0.98).

Applicable for infinite baffle? Viable, and it is the only thing that makes sense with a QTS so high. But at the same time, not a great idea due to low xmax.

T/S parameters