NVX SQW104

Overall summary

In this sample and under these test conditions, the 1 V baseline distortion rises sharply below 40 Hz, then becomes much lower and less variable through most of the desired subwoofer passband. The 1 V sweep shows a third-order dominated peak of about 7 percent THD, a smaller uneven region around 30 to 38 Hz, and generally about 1 percent or less through most of 40 to 120 Hz. Below about 25 Hz, higher order distortion traces are significant, while from roughly 30 to 120 Hz, H2 distortion is generally the stronger of the H2 distortion and H3 distortion traces, with H3 distortion staying relatively low.

At 18 V, the distortion character changes substantially. The bottom of the range rises to about 22 percent THD on the bottom end, then the main issue becomes a very broad H2 distortion-dominant rise through roughly 35Hz and above. H3 distortion is high enough to be of concern at the lower frequencies, thought H2 distortion still dominates, and continues to be dominant through the main 50 to 120 Hz region. This is important because distortion increases dramatically as the subwoofer is driven to more realistic output levels. By the time it reaches the high-level sweep, distortion is elevated enough across much of the passband that it becomes difficult to clearly separate which specific motor, suspension, or inductance nonlinearity is responsible for each artifact.

The LSI data explains a lot of that behavior. BL 70 percent occurs at 13.14 mm one way, but the BL curve is peaky, offset toward coil-in, and asymmetrical. CMS 50 percent was not reached inside the protection window, which is favorable, but the compliance behavior is still visibly offset. The largest clean excursion concern is inductance, with Le 17 percent occurring at only 4.28 mm one way, well before BL or CMS become the standard limiting factors.

For sealed enclosures, the manuafcturer wildly overstates the sealed enclosure sizes that it can handle, and is best understood as a compact shallow-mount subwoofer that trades normal Qtc behavior for space savings. The manufacturer recommended 0.50 ft³ sealed enclosure produces a high QTC of 0.924 on this sample, while a 0.707 Qtc requires 1.75 ft³.

Manufacturer's suggested use case

NVX positions the SQW104 as a 10 inch SQ-Series shallow-mount dual 4 ohm subwoofer with a polypropylene cone, rubber surround, custom tooled die-cast aluminum basket, 1.5 inch high temperature copper voice coil, and a 74 oz ferrite motor structure. The published ratings are 600 watts RMS, 1200 watts peak, 16 mm Xmax, 83 dB sensitivity, 25 to 500 Hz frequency response, 33 Hz Fs, 3.23 inch top-mount depth, and a recommended 0.50 ft³ sealed enclosure or 0.60 ft³ ported enclosure. Sonic Electronix, their sister company e-commerce retailer, also lists it as CTA-2031 compliant and notes that a protective grille is included.

Our suggested use case

Based on the data from this sample, it is difficult to identify a particularly compelling use case. The shallow-mount form factor suggests applications where mounting depth is limited, but the enclosure requirements and measured behavior work against that advantage. The manufacturer-recommended 0.50 ft³ sealed enclosure produces a high-Qtc alignment that is likely to result in a peaky response that isnt very usable, while achieving a more conventional 0.707 Qtc requires approximately 1.75 ft³, which largely defeats the packaging benefit of a shallow driver. When that enclosure requirement is considered alongside the elevated high-level distortion and the very early Le-based clean-stroke limitation, this sample does not present a strong alignment between its design goals and its measured performance. The 0.50 ft³ sealed recommendation is usable as the somewhat compact target, but it is a higher-Qtc result at 0.924, not a normal Qtc sealed setup. If a 0.707 Qtc is the target, this sample needs about 1.75 ft³, which removes much of the packaging advantage.

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: 18 volts volts

Approximate electrical power at that limit at 20Hz: ~180 watts. Real power varies with frequency and impedance. volts

Rated power (published): 600 watts

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ~30.0 percent. Hits 13.1 mm in free air with ~180 watts of power.

Claimed Xmax vs. measured at BL 70%: 13.14 mm one way, only 82.1 percent of the manufacturer claim of 16 mm

Xmax @ 50% Cms: >14.86 mm one way, greater than 92.9 percent of the manufacturer claim of 16 mm

Xmax @ 17% Le: 4.28 mm one way, only 26.8 percent of the manufacturer claim of 16 mm

Manufacturer suggested sealed enclosure size (and its resulting QTC): Suggested 0.50 ft³ nets a Qtc of 0.924

Required sealed enclosure for 0.707 QTC: 1.75 ft³ nets a 0.707 Qtc.

Xmax @ 50% Cms: >14.86 mm one way, greater than 92.9 percent of the manufacturer claim of 16 mm

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 harmonic distortion. 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-oct smoothing. Two drive levels, 1 V baseline and a high level set at 18 V per the under BL 70 percent rule derived from LSI for this unit. This sample in this test on this voltage level hit about 13 mm at 20 Hz in free air, below the accepted standard of 70 percent of BL. Distortion reported both as percent and by harmonic.

At 1 volt - baseline

In this sample and under these test conditions, the 1 V baseline is peaky below 40 Hz, with about 6.7 percent THD at 20 Hz. Distortion falls quickly through the 30s and stays near or below about 1 percent from roughly 40 to 120 Hz. Below about 25 Hz, higher order distortion traces are significant, while from about 30 to 120 Hz, H2 distortion is generally stronger than H3 distortion. The response rises into the 45 to 55 Hz region and then gradually tapers through the desired subwoofer passband.

At high level voltage (18 volts volts)

At 18 V, the distortion rises drastically. THD is about 22 percent at the very bottom of the frequency range with high amounts of H2 and H3 distortion, and has a broad H2 distortion-dominant band from about 35Hz and beyond. In that broad region, THD reaches roughly 15 percent at the main peaks. Overall, this is just a very high distortion driver.

Delta - 1 volt distortion vs. high level distortion

Compared with 1 V, the 18 V sweep shows a broad increase in H2 distortion from about 30 to 120 Hz rather than a simple overall rise. H2 becomes the dominant distortion through most of the passband, while H3 remains secondary except at the lowest frequencies. This behavior is consistent with the measured BL and CMS asymmetry, and the early Le limit remains the main large-signal constraint.

What this means in practice

At 18 V, this sample can produce output, but not clean output across the desired subwoofer passband. The high-level sweep shows very high distortion across the entire usable frequency range for this subwoofer.

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 13.14 mm one way on this sample. The BL curve is peaky and offset toward coil-in rather than shaped like a flat centered plateau. The coil-in side rolls off more gradually, while the coil-out side loses force more quickly after center. That shape concentrates the highest force into a narrower and offset region, which matches the elevated H2 distortion behavior when combined with the measured asymmetry.

Bl(x) symmetry

LSI reports a BL symmetry point of -1.90 mm and 16.02 percent BL asymmetry at xprot. The curve is biased toward coil-in, with more force loss on the coil-out side. In this sample, that asymmetry is consistent with the H2 distortion-dominant high-level sweep. This is not a perfectly centered BL system under the test conditions.

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 protection window; the table lists >14.86 mm one way, and the LSI comment says CMS resolved to 57 percent. That is favorable relative to the BL and Le limits because the suspension is not the first large-signal limit. The compliance curve is broad through much of the center range, then rolls down at higher displacement. It is not a perfectly centered curve, but it does not collapse early inside the tested protection window.

Cms(x) symmetry

Kms symmetry reports 38.47 percent asymmetry at xprot, and the visual CMS behavior shows the suspension is not centered perfectly. The compliance peak is shifted toward coil-in, while the far coil-out side loses compliance at higher stroke. This can contribute even order distortion, but CMS is not the primary limit in this sample. The more important practical issue is that the suspension still allows more stroke than the inductance behavior supports cleanly.

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

Large-signal cold Le at rest is 1.58 mH. Le(x) changes strongly with position, rising toward coil-in and falling toward coil-out. The 17 percent Le variance criterion occurs at only 4.28 mm one way, which is much earlier than the BL 70 percent and CMS 50 percent limits. Based on the inductance behavior, there is no indication of inductance management measures on this driver, and this can be one of the reasons for the elevated distortion.

Current dependence

Le(i) rises from about 1.36 mH at negative current to about 1.90 mH at positive current, so current dependence is moderate to strong and adds another level-dependent variable 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

Large-signal cold Qts near center is 0.56, while large-signal warm Qts near center is 0.70. The Qts(x) curve is asymmetric; it dips on the coil-in side and rises strongly toward coil-out at higher stroke. That means damping changes with displacement in an asymmetric manner instead of staying stable. The shift is mainly a large-stroke behavior and may help explain why the high-level result changes character instead of simply scaling up from the 1 V baseline.

LSI takeaway

In this sample and under these test conditions, the earliest limiting mechanism is Le 17 percent at only 4.28 mm one way. The BL curve is peaky and offset, with 16.02 percent asymmetry at xprot, which is consistent with the dominant H2 distortion seen at high level. CMS 50 percent was not reached inside the protection window, but the compliance behavior is not perfectly centered and can still add even order distortion. Inductance changes strongly with position and moderately to strongly with current, which reduces the usable clean stroke before BL or CMS become the standard limit. Qts rises substantially toward coil-out, so damping changes at higher excursion rather than staying stable.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.50 ft³ sealed nets a Qtc of 0.924 on this sample.

Sealed volume required for 0.707 QTC on this sample: 1.75 ft³

Applicable for infinite baffle? Not recommended. The Le 17 percent limit is very early, and infinite baffle removes the sealed air spring that helps control low frequency excursion.

T/S parameters