Trulli TD10S

Overall summary

In this sample and under these test conditions, the Trulli TD10S shows elevated distortion even at the 1 volt baseline. The 1 V distortion curve is peaky through the lowest part of the desired subwoofer passband, with high THD around 20 Hz, a strong peak near 28 Hz, and a smaller narrow rise near 60 Hz. Below approximately 25 Hz, H3 distortion is the stronger contributor, while H2 distortion becomes the main feature around the 25 to 30 Hz region. Above that range, the curve drops, but it does not become especially low through the main 30 to 120 Hz region. At the 6.5 volt high-level sweep, THD rises heavily at the bottom of the band, reaching about 15 percent at 20 Hz, about 5 percent near 30 Hz, and about 3 percent near 50 Hz.

The LSI data shows a measured BL 70 percent limit of 8.53 mm one way and a CMS 50 percent limit of 8.34 mm one way, both landing close to the manufacturer’s published 9 mm Xmax claim. BL symmetry is good, while CMS shows slight asymmetry toward the inward stroke. Le is low at rest and stable with current, and the 17 percent Le criterion is not reached before the protection ceiling. This means the elevated distortion seen in the TRF data is not mainly explained by an early Le limit or by the high-level sweep exceeding the large-signal displacement limits.

For sealed use, this sample calculates to Qtc 0.87 in the manufacturer’s 0.35 ft³ compact sealed recommendation and Qtc 0.62 in the manufacturer’s 1.0 ft³ ideal sealed recommendation. A 0.707 Qtc target lands at about 0.65 ft³ based on the large-signal cold parameters. The practical result is a very shallow 10 inch subwoofer that fits where many conventional subwoofers will not, but with limited clean low-frequency headroom from a single driver.

Manufacturer's suggested use case

Trulli positions the TD10S as an ultra-shallow 10 inch subwoofer using its patented ThinDriver perimeter-driven motor, a large 7 inch CCAW voice coil on a glass fiber former, a custom three-layer foam diaphragm, silicone rubber surround, and an N52 neodymium magnet array. Published specifications list a 2 ohm nominal impedance, 288 watt nominal power rating, 600 watt program/music rating, 1000 watt peak rating, 83 dB sensitivity at 1 W/1 m, 20 Hz to 400 Hz frequency range, 9 mm one way Xmax, 14 mm Xmech, and 2.18 inch mounting depth. Published sealed enclosure information includes compact sealed use around 0.35 ft³ and ideal sealed use around 1.0 ft³ on the website, while the cut sheet also lists sealed examples from 0.25 ft³ to 0.70 ft³.

Our suggested use case

Based on the data, this sample is best limited to sealed enclosures where shallow depth is the primary constraint. The 0.35 ft³ compact sealed recommendation produces a higher Qtc on this sample, while the 1.0 ft³ recommendation produces a lower Qtc, and a 0.707 Qtc target lands between them at about 0.65 ft³. This is not a strong single-driver choice for applications that need clean low-frequency output at 20 Hz. Infinite baffle is not recommended because the driver has limited one way linear stroke, modest cone area, low Qts, and would lose the mechanical support of the sealed air spring.

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: 6.5 volts volts

Approximate electrical power at that limit at 20Hz: Approximately 21 watts. Real power varies with frequency and impedance. volts

Rated power (published): 288 watts nominal

Power used to hit the standardized limits in free air, relative to their xmax rating free air: Approximately 35 watts at 20 Hz to reach the BL 70 percent limit of 8.53 mm one way in free air, about 12.2 percent of the 288 watt nominal rating. Real power varies with frequency and impedance.

Claimed Xmax vs. measured at BL 70%: 8.53 mm one way measured at BL 70 percent, 94.8 percent of the manufacturer’s 9 mm claim.

Xmax @ 50% Cms: 8.34 mm one way, 92.7 percent of the manufacturer’s 9 mm claim.

Xmax @ 17% Le: >8.76 mm one way. The Le 17 percent criterion was not reached before the protection ceiling on this sample.

Manufacturer suggested sealed enclosure size (and its resulting QTC): 0.35 ft³ sealed nets Qtc 0.87 on this sample.

Required sealed enclosure for 0.707 QTC: 0.65 ft³ nets Qtc 0.707 on this sample.

Xmax @ 50% Cms: 8.34 mm one way, 92.7 percent of the manufacturer’s 9 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 Klippel LSI used for large-signal parameters. The nearfield microphone was placed at 1/10 cone diameter plus 2 inches, on axis. Response was measured to 1 kHz and THD was measured to 500 Hz, both with 1/6 octave smoothing. One sweep was performed at 1 V for baseline, and the high-level sweep was performed at 6.5 volts, set just under the BL 70 percent limit from LSI. During the high-level sweep, this sample reached approximately 4.6 mm one way at 20 Hz in free air.

At 1 volt - baseline

The 1 V distortion curve is peaky below 40 Hz, with elevated THD at 20 Hz and a strong rise around 28 Hz. H3 distortion is strongest below approximately 25 Hz, while H2 distortion becomes the stronger contributor around the 25 to 30 Hz region. A smaller narrow rise appears near 60 Hz, after which the 30 to 120 Hz range remains lower than the bottom octave but not especially clean. The baseline result matters because the elevated distortion is already visible at very low drive, not only after the driver is pushed toward its stroke limits.

At high level voltage (6.5 volts volts)

At 6.5 volts, THD rises substantially at the bottom of the band and reaches about 15 percent at 20 Hz. H3 distortion is the dominant component below approximately 25 Hz, which is a negative result because the third harmonic remains strong in the lowest operating range. Around 25 to 30 Hz, H2 distortion becomes dominant, and THD is about 5 percent near 30 Hz. By roughly 50 Hz, THD is about 3 percent, with H2 distortion still carrying much of the distortion profile through the main 30 to 120 Hz band. The high-level result does not show a single isolated distortion feature that explains the result by itself. It is better described as broadly elevated distortion through the low bass, with the harmonic balance shifting from H3 distortion at the bottom to H2 distortion through much of the remaining subwoofer band.

Delta - 1 volt distortion vs. high level distortion

Compared with 1 V, the high-level sweep does not simply reveal a new isolated problem. The same general low-frequency roughness remains, but the curve lifts heavily at the bottom and the harmonic balance becomes more clearly split by frequency. H3 distortion stays dominant below approximately 25 Hz, while H2 distortion becomes dominant around 25 to 30 Hz and remains the main contributor through much of the main band. The smaller 1 V peak near 60 Hz does not become the main high-level feature, so the high-level behavior is not primarily defined by that narrow baseline rise.

What this means in practice

At the 6.5 volt high-level sweep, this sample measured about 15 percent THD at 20 Hz, about 5 percent near 30 Hz, and about 3 percent near 50 Hz. H3 distortion dominates the lowest part of the band, while H2 distortion becomes dominant through much of the remaining desired subwoofer passband. The high-level result shows limited clean low-frequency headroom from a single driver rather than a single narrow problem area.

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 8.53 mm one way. The BL curve stays near its upper range through the center of travel, then falls normally toward both ends of the measured stroke window. In absolute terms, the usable BL window is modest, which is expected for a driver this shallow.

Bl(x) symmetry

The test engineer note states “Good BL symmetry.” The table reports the BL symmetry point at -0.70 mm at xprot, with BL asymmetry of 14.20 percent. This is not the dominant issue in the measured data, especially compared with the distortion level appearing while the driver is still operating below the BL 70 percent limit.

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 occurs at 8.34 mm one way. The suspension reaches its standardized limit slightly before BL 70 percent, making CMS the first of the two displacement-based limits on this sample. The compliance behavior shows a usable window close to the published Xmax claim, but it is still modest in absolute stroke. This is one of the key mechanical constraints for low-frequency output from a single unit.

Cms(x) symmetry

The test engineer note states “Slight CMS asymmetry towards the inward stroke.” The table reports stiffness asymmetry of -28.39 percent at xprot. That inward bias is directionally consistent with H2 distortion becoming the stronger contributor around 25 to 30 Hz, but the TRF distortion appears before the driver is pushed past the CMS 50 percent boundary.

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 0.40 mH cold. Le(x) changes with position, but the 17 percent Le criterion is not reached before the 8.76 mm protection ceiling on this sample. Inductance is low in level compared with many subwoofers, and it does not set the practical clean one way limit here. Based on this behavior, Le is not the main explanation for the elevated high-level distortion in the 20 to 120 Hz range.

Current dependence

Le(i) is very stable with current over the plotted range.

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 0.37 cold near center and 0.38 warm near center, showing essentially no meaningful change in the center value with heating. The Qts(x) curve remains relatively symmetrical in both directions of travel. However, Qts increases substantially as excursion moves away from center in either direction, indicating a fairly significant change in damping behavior at higher stroke levels. While the symmetry of the curve suggests the effect is somewhat balanced between positive and negative excursion, the magnitude of the rise means damping is not especially stable at large excursions and can contribute to response and compression changes under higher drive conditions.

LSI takeaway

On this sample, CMS 50 percent is the first standardized displacement limit, at 8.34 mm one way. BL 70 percent lands close behind it, with good BL symmetry and no early BL-driven failure point in the high-level sweep. CMS shows a slight inward bias, which is consistent with the H2 distortion contribution around 25 to 30 Hz. Le is low at rest, does not cross the 17 percent criterion before the protection ceiling, and is stable with current. Qts rises with stroke, so damping changes as the driver moves toward the ends of its usable travel.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: 0.35 ft³ sealed nets Qtc 0.87 on this sample.

Sealed volume required for 0.707 QTC on this sample: Approximately 0.65 ft³ nets Qtc 0.707 on this sample.

Applicable for infinite baffle? Not recommended. This sample has limited one way linear stroke, modest cone area, low Qts, and would lose the mechanical excursion control provided by a sealed enclosure.

T/S parameters