Helix IK S10

Overall summary

In this sample and under these test conditions, the HELIX IK S10-DVC2 shows a very clear split between its mechanical suspension behavior and its inductance behavior. At 1 V, the distortion plot is mostly controlled above the lowest part of the sweep, but there is a narrow and abnormally high THD spike around the mid 20 Hz range that reaches about 15-16 percent. Above roughly 35 to 40 Hz, baseline THD drops and remains relatively normal through the rest of the frequency range. H2 distortion is the main contributor through the low-frequency spike, while H3 distortion shows a smaller local rise around the low 30 Hz range.

At 11 V, the distortion character changes from one narrow low-frequency baseline spike into a broader rise across the operating band. THD is highest near 20 Hz at about 16 percent, then settles around the 9 percent range through much of the 40 to 120 Hz band. H3 distortion is more elevated, and even becomes the highest contributor at the very bottom of the frequency range, which lines up with the early Le-based excursion limit shown in the LSI data. H2 distortion becomes the stronger component through much of the higher frequency range, which is consistent with the measured BL asymmetry shown in the LSI data. The high-level sweep does not show a single new narrow failure point in the main subwoofer range, but it does show that distortion rises broadly and drastically once the driver is pushed near its standardized free-air excursion limit.

The LSI results are the main story here. BL 70 percent lands at 7.12 mm one way, which is above the manufacturer’s 6 mm xmax claim. CMS 50 percent is not reached inside the 7.74 mm protection window. As a matter of fact, CMS did not really resolve, which is usually favorable (at least when you are pushing the driver to its other limits), and matches the test engineers supplied note that the suspension is not the limiting mechanism here. In practical terms, the suspension is mostly acting as a centering and control element through the measured window rather than becoming a hard progressive limit that is introducing distortion. The first and main limiting factor is inductance, with the 17 percent Le criterion occurring much earlier at 3.79 mm one way, which is most likely a contributor to the high H3 distortion seen at the lower frequencies.

For sealed use, the manufacturer’s 0.5 ft³ recommendation calculates to a Qtc of 1.00 on this sample. A 0.707 Qtc requires 2.2 ft³ based on the large signal cold parameters. That means the manufacturer’s recommended enclosure is usable for compact sealed installations, but it is a high-Q alignment that is peaky without much low end extension. To be fair, I do not think low end extension is the main goal with this subwoofer.

Manufacturer's suggested use case

Audiotec Fischer, parent company of Helix, positions the IK S10-DVC2 as a shallow 10 inch subwoofer for compact and shallow enclosure designs. The manufacturer lists a 2 x 2 ohm dual voice coil configuration, 300 watt RMS and 600 watt maximum power handling, 6 mm one way xmax, 87.0 dB sensitivity at 1 W / 1 m, 90.0 dB sensitivity at 2.83 V / 1 m, and an 84.5 mm mounting depth. Construction features include a stiff sandwich paper cone, rubber surround, 50.8 mm voice coil, protective grille, included gasket, included enclosure terminal, and a rear threaded M6 mounting point intended to secure the motor to the back of the enclosure and reduce enclosure vibration.

The manufacturer recommends the IK S10-DVC2 for sealed and vented compact enclosures. The published sealed recommendation is 14 L, about 0.5 ft³, with a listed -3 dB point of 46 Hz and recommended DSP settings. The published vented recommendation is 16 L, tuned to 37 Hz, with a listed -3 dB point of 39 Hz and its own recommended DSP settings. The stated use case is clearly compact, shallow subwoofer duty where installation depth and enclosure size are major constraints.

Our suggested use case

Based on the data, this sample is best used in compact sealed enclosures where shallow depth matters more than maximum low-frequency output. The manufacturer’s recommended 0.5 ft³ sealed enclosure produces a Qtc of 1.00 on this sample, which is a compact, higher-Q sealed alignment. A larger 2.2 ft³ enclosure is required for 0.707 Qtc, but that starts to work against the main reason someone would choose this driver, which is shallow packaging.

The BL and CMS results are favorable relative to the published 6 mm xmax claim, especially because CMS 50 percent is not reached inside the measured protection window. The practical limitation is Le(x), which reaches the 17 percent inductance criterion at only 3.79 mm one way. That does not mean the driver cannot be used beyond that point, but it does mean the cleanest part of its operating range is set by inductance behavior rather than mechanical suspension travel or BL loss. For users chasing more clean output, multiples would be a better path than trying to force a single driver to carry a high-output low-bass role.

To me, based on the data and my personal experience with this subwoofer, it is best used as a very simple addition to basic systems to add SOME sort of low end.

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: 11 V volts

Approximate electrical power at that limit at 20Hz: Approximately 35 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: The 11 V high-level TRF sweep used approximately 35 watts, about 11.7 percent of the 300 watt published RMS rating. This sample reached approximately 7.1 mm one way at 20 Hz in free air during that sweep, essentially matching the 7.12 mm BL 70 percent limit. Real power varies with frequency and impedance.

Claimed Xmax vs. measured at BL 70%: 7.12 mm one way, 118.7 percent of the manufacturer’s 6 mm claim.

Xmax @ 50% Cms: >7.74 mm one way, greater than 129.0 percent of the manufacturer’s 6 mm claim.

Xmax @ 17% Le: 3.79 mm one way, 63.2 percent of the manufacturer’s 6 mm claim.

Manufacturer suggested sealed enclosure size (and its resulting QTC): Claimed 0.5 ft³ nets a Qtc of 1.00.

Required sealed enclosure for 0.707 QTC: 2.2 ft³ nets a 0.707 Qtc.

Xmax @ 50% Cms: >7.74 mm one way, greater than 129.0 percent of the manufacturer’s 6 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: Nearfield mic positioned at 1/10th 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 V baseline and a high level set at 11 V per the under BL 70 rule derived from LSI for this unit. This sample in this test at this voltage level hit approximately 7.1 mm one way excursion at 20 Hz in free air, essentially at the 70 percent BL reference. Distortion is reported both as percent and by harmonic.

At 1 volt - baseline

The 1 V distortion curve has one main low-frequency spike rather than a broadly elevated distortion band, though the 30-45hz region isn't pretty either. THD rises to about 15-16 percent around the mid 20 Hz range, then falls in the mid 30 Hz range. Above roughly 40 Hz, THD remains relatively normal through most of the main subwoofer band. H2 distortion is the dominant contributor through the low-frequency spike, while H3 distortion shows a smaller local rise around the low 30 Hz range. The useful takeaway is that the very high baseline distortion issue is concentrated at the bottom half of a subwoofers intended frequency range rather than spread across the full 20 to 120 Hz region.

At high level voltage (11 V volts)

At 11 V, the distortion shape changes from a mostly isolated low-frequency baseline spike into a much broader and problematic high-level distortion rise. THD is again highest at the bottom of the sweep, around 16 percent near 20 Hz, but it does not collapse to the same lower level seen at 1 V once frequency rises.

Through much of the 40 to 120 Hz range, THD stays around the 9 percent region. H3 distortion is more involved at the lowest frequencies, which is consistent with the early Le-based limit in the LSI data. H2 distortion becomes the stronger component through much of the midbass, which is consistent with the measured BL asymmetry in the LSI data. The flat cone could also be a contributor, but it is difficult to say.

The high-level distortion result does not show a single new narrow failure point in the main passband, but it does show a broad and general rise in distortion as the driver is pushed near its standardized free-air stroke limit.

Delta - 1 volt distortion vs. high level distortion

The main change from 1 V to 11 V is that distortion becomes elevated on a broad frequency range at higher excursion. The 1 V sweep has one significant low-frequency spike, while the 11 V sweep carries elevated THD through the entire intended use frequency range. Harmonic balance also shifts with level, with H3 distortion becoming more important at the lowest frequencies and H2 distortion becoming the main component through much of the upper bass and lower midbass area. The LSI data supports that interpretation because Le(x) is the earliest standardized limit, while BL asymmetry is also present and can contribute to even-order content. This means the high-level sweep is not just the 1 V curve scaled upward, the driver’s nonlinear mechanisms become more visible as stroke increases. The drivers flat cone may also be a contributor to this rise in distortion across a wider frequency range, but it is difficult to say for sure with the data that we have.

What this means in practice

At usable levels, this sample should be treated as a compact shallow driver with minimal stroke due to an early inductance-based limit. The suspension is not the limiting factor in the measured range, which is favorable for avoiding the hard progressive-stiffness behavior that often shows up in most subwoofers. The tradeoff is that Le(x) becomes the practical clean stroke ceiling before BL or CMS. H3 distortion is most relevant at the lowest frequencies, while H2 distortion is more relevant through much of the midbass at higher drive.

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 7.12 mm one way. The BL curve is usable past the manufacturer’s 6 mm xmax claim, but it is not a flat plateau. It has a rounded, peak-centered shape and loses force as travel increases, with the coil-in side becoming the limiting side first. This supports the idea that the published 6 mm xmax claim is mechanically conservative by the project’s BL standard.

Bl(x) symmetry

The table reports the BL symmetry point at 0.91 mm at xprot, with BL asymmetry of -19.25 percent. That is enough asymmetry to matter, especially as the driver approaches the protection window. This can contribute to H2 distortion at higher drive levels, which matches the high-level TRF data where H2 distortion becomes the stronger component through much of the midbass. BL is not the earliest limit, but its asymmetry is still part of the distortion picture.

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 inside the 7.74 mm protection window. The LSI note says CMS only resolved to 92 percent and that the CMS data is likely not valid because of poor resolution, so the exact compliance shape should not be over-interpreted. The practical takeaway is still useful: the suspension did not become the limiting mechanism within the measured excursion window. That is usually favorable from a distortion and linearity perspective because it means the design is not relying on a rapidly stiffening suspension to protect the driver inside the normal test range, and said stiffening suspension is not adding its usual non-linearity to the system.

Cms(x) symmetry

The table reports stiffness asymmetry of 8.51 percent at xprot. That is not perfectly centered, but it is not the dominant limitation in this sample. Given that CMS 50 percent was not reached and the CMS result did not fully resolve, the suspension symmetry should be taken with a grain of salt. The stronger issue is Le(x), followed by BL asymmetry.

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 1.68 mH cold. The Le(x) curve changes heavily with position, sitting much higher on coil-in travel and falling substantially through coil-out travel. The 17 percent Le variance criterion occurs at 3.79 mm one way, making it the earliest of the three standardized limits on this sample. Based on the inductance behavior, it's pretty clear that there are no inductance management features in this motor design.

Current dependence

Le(i) rises with current over the plotted range, from roughly the low 1.6 mH region to the low 1.8 mH region. That current dependence is not as severe as the position dependence, but it is still not ruler-flat. In practice, Le(x) is the larger issue because it sets the earliest standardized displacement limit. This is consistent with the high-level TRF data showing H3 distortion becoming more important at the bottom of the sweep.

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 is 0.56 cold near center and 0.59 warm near center. The Qts(x) curve is lowest near center, then rises in both directions as excursion increases. The rise is stronger on the coil-in side, reaching about 1.0 near the inward end of the test window, while the coil-out side rises closer to the high 0.8 range. That means damping changes noticeably with stroke, and the change is not symmetrical, but its not terrible overall in comparison to other subwoofers we have tested.

LSI takeaway

The earliest standardized limit is the Le 17 percent criterion at 3.79 mm one way, making inductance position dependence the primary linearity limitation in this sample. BL 70 percent occurs at 7.12 mm one way, supporting the published 6 mm xmax claim, while CMS 50 percent was not occur within the 7.74 mm protection window. Because the CMS data only resolved to 92 percent, the suspension should be viewed as non-limiting within the measured range rather than fully characterized. BL asymmetry and the changing Qts(x) curve become secondary contributors as excursion increases, but the dominant practical limitation remains Le(x).

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.5 ft³ nets a Qtc of 1.00 on this sample.

Sealed volume required for 0.707 QTC on this sample: 2.2 ft³ nets a 0.707 Qtc on this sample.

Applicable for infinite baffle? Not recommended for this driver as there is not enough usable clean stroke.

T/S parameters