Sundown Audio Zv5 12

Overall summary

In this sample and under these test conditions, the 1 V baseline distortion from 20 to 120 Hz is elevated below 40 Hz, with a primary peak of about 6 percent THD at 20 Hz and a smaller peak of about 2 percent THD around the upper 30’s. Through most of 20 to 30 Hz, H2 distortion is dominant, with H3 distortion rising close behind in the mid-20 Hz region as total distortion falls. From 40 to 80 Hz, baseline distortion is much lower and H2 distortion remains the dominant harmonic. Through roughly 50 to 120 Hz, total distortion stays under about 1% with a gradual rise approaching the upper end of the shown band.

The high level sweep at 45 V shows higher distortion across essentially the full 20 to 120 Hz band, and it keeps the same general character as the 1 V sweep rather than introducing a new problem frequency. The lowest octave remains the hardest region, but the bigger change at high level is harmonic balance as frequency rises, H3 distortion becomes a meaningful contributor and is the main issue in the upper bass region above about 50 Hz. Please note, this high level sweep did not reach the standardized BL 70 percent limit on this unit and reached only about 27.5 mm one way at 20 Hz in free air, so the high level distortion numbers shown here are likely lower than what many users will see when driving the driver closer to its full capability.

Klippel LSI on this unit shows great BL linearity and symmetry, with a very broad BL(x) shape and a BL symmetry point of -2.07 mm at the xprot limit. In contrast, the suspension behavior does not support the manufacturer’s “linear suspension” positioning, with CMS behavior over stroke being extremely non linear and the IEC stiffness asymmetry metric landing at 35.66%, which lines up with the dominant H2 distortion seen in the TRF sweeps. Inductance also varies strongly with position and crosses the 17 percent criterion much earlier than the BL or CMS limits, so clean stroke is inductance limited by the standardized criteria in this sample, and this aligns with H3 distortion remaining relatively strong as drive rises. Le(i) current dependence is relatively low in the LSI data, and Qts is shifted coil-in and rises quickly with stroke with no real flat region.

The manufacturer does not recommend sealed enclosures for this model, but since that is all we focus on here, a 0.707 Qtc target on this sample is reached in a very small ≈0.24 ft³ sealed enclosure using the large signal cold parameters. Larger than typical 0.707 Qtc sealed enclosures would be advised due to the air spring severely limiting xmax. This is a rare case where we recommend this as this is more of an SPL subwoofer as opposed to sound quality, but we figured it would be fun to test both. Any enclosure conclusions here are specific to this unit and the cold-state parameters used for the calculations.

Manufacturer's suggested use case

The manufacturer positions the Zv5 12 as an ultra-high excursion subwoofer intended for low-frequency output in ported enclosures. Sealed enclosures are listed as not recommended, while a 2.50 ft³ ported enclosure is listed with a recommended 32 Hz tuning and 40 sq in port area. RMS power handling is listed as 2000 watts, published sensitivity is 83.4 dB at 1 W/1 m, and Xmax is listed as 35 mm one way by 70% BL. The product description highlights a triple-stacked 234 mm motor, a 3 inch 4-layer flat-wire aluminum voice coil, and a Faraday ring for inductance control. In short, this thing is designed to move a lot of air and to generate a lot of volume.

Our suggested use case

In this sample and under these test conditions, sealed enclosures are technically workable when targeting a higher Qtc, but achieving 0.707 Qtc requires a very small enclosure volume of ≈0.24 ft³ based on the large signal cold parameters. The only thing is, the combination of parameters that allow for a super small sealed enclosure also make it inefficient in that small enclosure, and requires 10,800 watts to reach its ~37mm xmax. If a larger sealed enclosure is used, system Qtc will be well below 0.707 and the overall sealed response shape will change accordingly, but power requirements will become somewhat realistic. That said, this unit is Le-limited by the 17 percent criterion before BL or CMS, so using multiple drivers can reduce per-driver stroke and improve clean headroom. Infinite baffle is not recommended here because removing the sealed air spring reduces mechanical headroom, and this sample’s already extremely low Qts.
That said, it is still not exactly designed for what most are trying to do, so typical sealed enclosure use in a SQ system is probably not a great idea.

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 – Note that the amplifier used wasnt enough to push BL past its 70% limit, and was only able to hit 79% BL, but it was close. BL only reached 79%

High-level sweep limit for this sample: 45 volts

Approximate electrical power at that limit at 20Hz: 1350 watts at 1.5 ohms. Real power varies with frequency and impedance. volts

Rated power (published): 2000 watts is what I was able to find online.

Power used to hit the standardized limits in free air, relative to their xmax rating free air: ≈67.5% of the published 2000 watt rating (based on ≈1350 watts at the high-level sweep limit). Real power varies with frequency and impedance.

Claimed Xmax vs. measured at BL 70%: Estimated ≈37.00 mm one way for this unit based on the BL curve behavior past the measured 79% point (34.62mm), which is 105.7% of the manufacturers xmax 35mm claim.

Xmax @ 50% Cms: 34.36 mm one way at CMS 50%, which is 98.2% of the manufacturers 35 mm xmax claim.

Xmax @ 17% Le: 22.43 mm one way at Le 17%, which is only 64.1% of the manufacturers 35 mm claim. This is the practical clean one way limit for this sample by the standardized criteria.

Manufacturer suggested sealed enclosure size (and its resulting QTC): Sundown does not recommend sealed enclosures for these subwoofers. Using the cold large signal parameters from the LSI test, this subwoofer will have a 0.707 QTC in a 0.24 ft³ sealed enclosure. Super small sealed enclosure predictions are common with SPL-intended subwoofers due to extremely low QTS.

Required sealed enclosure for 0.707 QTC: 0.24 ft³ nets a 0.707 QTC.

Xmax @ 50% Cms: 34.36 mm one way at CMS 50%, which is 98.2% of the manufacturers 35 mm xmax 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: 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-oct smoothing. Two drive levels, 1 V baseline, and a high level set at 45 V per the under BL-70 rule derived from LSI for this unit (again, please note that this was the power limit of the amplifier module that we have for the Klippel. This did not push this subwoofer to its limits as much as it did with every other subwoofer in the test). This sample in this test on this voltage level hit 27.5 mm of excursion at 20hz in free air, below the accepted standard of 70% 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 THD curve is relatively rough below about 40 Hz, it is not just a single bump, it is a mix of a low-end rise plus a smaller upper-30 Hz peak. Even at this low drive level, H3 distortion runs unusually close to H2 distortion through much of the 20s, which is a flag that odd-order distortion is already a meaningful contributor, not something that only shows up when pushed hard. Through the midbass region the total distortion stays low, but the harmonic balance still leans toward H3 distortion more than is typical for a subwoofer that is being described as “very low distortion.” Net result at 1 V is that the overall shape looks more like a driver with meaningful odd-order behavior baked in, rather than a clean baseline that only degrades at high output.

At high level voltage (45 volts)

In this sample and under these test conditions, the 45 V sweep keeps the same general character as the 1 V sweep, it is not a “new problem appears at high level” situation. The main change is that the whole curve lifts, and the lowest octave remains the hardest region, but the bigger story is harmonic balance, H3 distortion stays relatively strong and becomes the main contributor above about 50 Hz. That matters because it means the upper bass region is not only getting louder distortion-wise, it is also skewing toward odd-order distortion as drive rises, which is usually more objectionable than a similar amount of even-order distortion. In other words, the graph is not just saying “more THD,” it is saying “more THD with more of it coming from H3 distortion,” especially as you move up in frequency.

Delta - 1 volt distortion vs. high level distortion

Compared with 1 V, the 45 V sweep shows the expected broad increase in distortion, but it does so without any obvious narrow, level-invariant spike that would point to a fixed resonance artifact dominating the result. The useful takeaway is that the distortion increase looks primarily level-driven rather than being dominated by a single discrete problem frequency. At the same time, the way H3 distortion grows relative to the baseline indicates that odd-order distortion is a core limitation as the driver is pushed, especially in the upper bass portion of the plotted passband.

What this means in practice

At high level, this driver’s distortion does not just increase, it shifts toward relatively higher H3 distortion contribution as frequency rises, and that is the main concern with this sample’s behavior. The standardized clean stroke ceiling is set by inductance variation rather than BL or CMS, which lines up with H3 distortion remaining a meaningful piece of the distortion story as drive increases. If more clean headroom is needed at similar output targets, using multiple drivers can reduce per-driver stroke and reduce inductance-driven nonlinearity.

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

Note, the amplifier we have for the Klippel LSI module wasn’t powerful enough to get this behemoth of a subwoofer to fully reach its BL 70% limit. BL 70 percent is estimated to be about 37 mm one way for this unit based on the BL(x) curve shape, since the measurement only reached 79% BL at 34.62 mm within xprot. The BL(x) curve is very broad and wide and features a gradual rolloff toward both excursion extremes over the measured window. This indicates a relatively wide central region of higher force factor rather than a narrow shelf. This is a very good BL curve.

Bl(x) symmetry

At xprot (protection limit), the BL symmetry point is -2.07 mm, indicating an inward bias at high stroke, and the IEC BL asymmetry metric is 7.96%. BL asymmetry possibly relates with even-order H2 distortion and matches the TRF observation that H2 distortion is dominant across most of 20 to 120 Hz. This sample’s BL(x) behavior is not perfectly centered at high stroke in the LSI symmetry summary, but overall is pretty symmetrical relatively speaking.

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 34.36 mm one way, which is near the end of the available xprot window and is favorable in the sense that compliance does not compress early in the measured range. That said, CMS over stroke is extremely non linear, which is surprising because the manufacturer markets the “Mega” suspension that is featured on this subwoofer is extremely linear. Note about this: a third party who associates heavily with the brand (is featured all over the Sundown website) supplied us with a conflicting CMS/KMS graph for this subwoofer, but they didn’t realize that the graph that they had showed did not resolve with any confidence (this is a very in depth subject on the Klippel that we do not really cover, but we can if enough people are interested). I’m not saying that the company is using poor measurements to incorrectly assume that their suspension is very linear, but I don’t have anything else to work with to figure out where they might be coming up with this claim/description.

Cms(x) symmetry

The suspension asymmetry metric is not good, landing at 35.66%, and the stiffness symmetry plot shows the symmetry point shifting with stroke rather than remaining centered. Suspension asymmetry correlates with even-order H2 distortion, which is consistent with the dominant H2 distortion seen in both TRF sweeps. A specific mm symmetry-point value for CMS is not provided in the LSI summary table.

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 0.74 mH (cold). Le(x) shows a high position dependence, with inductance dropping on the coil-in side and rising through the mid stroke on the coil-out side. The 17 percent Le variance criterion is crossed at only 22.43 mm one way excusion, which is earlier than the CMS and BL criteria and sets the practical clean one way limit for this sample by the standardized limits by a pretty wide margin.

Current dependence

Le(i) current dependence is low in the measured current range, with only a small change in inductance as current swings positive and negative. Not bad, not great.

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

At rest, Qts is 0.24 cold and 0.28 warm in this unit. The Qts(x) curve features no real range where it is flat/linear, and is shifted towards coil in. This relatively poor QTS curve is most likely caused by a combination of things related to the suspension. First, the suspension being very stiff becomes more of a contributing factor to QTS than normal, and second, combining that with the poor CMS curve, we have our explanation for the non-linear QTS(x) curve.

LSI takeaway

In this sample and under these test conditions, the practical clean stroke ceiling is set by the 17 percent Le variance criterion at only 22.43 mm of one way excursion. BL linearity looks very favorable in the measured window with a broad BL(x) shape, and the estimated BL 70 percent point is about 37 mm one way, but near the stroke limits the BL symmetry point shifts to -2.07 mm and is not perfectly centered. CMS 50 percent does not occur until near the end of the xprot window at 34.36 mm one way, but the suspension behavior over stroke is extremely non linear and the suspensions asymmetry metric of 35.66% is not good, which lines up with the dominant H2 distortion seen in the TRF sweeps. Inductance shows high position dependence on this unit, while Le(i) current dependence is relatively low, and this combination helps explain why H3 distortion is a meaningful contributor as drive rises. Qts is 0.24 cold and 0.28 warm at center, but Qts(x) is shifted coil-in and shows no flat region, which is consistent with the suspension behavior on this sample.

Enclosure alignment calculations

Manufacturer sealed enclosured recommendations and the resulting QTC: Sealed enclosures are not recommended by the manufacturer.

Sealed volume required for 0.707 QTC on this sample: 0.24 ft³ sealed results in 0.707 QTC on this sample (large signal cold parameters).

Applicable for infinite baffle? Not recommended for infinite baffle in this sample due to the low Qts (0.24), which would result in a very low Qtc without a sealed air spring.

T/S parameters