Seas W18NX-001

*Photo courtesy of Madisound Speaker Store.

Up for test is a Seas W18NX-001.  This is another driver that will be party of Jerry Niebur’s Midwoofer Subjective Shootout next month.

As always, please see my Test Setup and Methods page regarding test criterion.

Let’s get to the data and analysis…


Theile-Small Parameters & Impedance

Electrical Parameters
Re 5.79 Ohm electrical voice coil resistance at DC
Krm 0.1518 Ohm WRIGHT inductance model
Erm 0.31 WRIGHT inductance model
Kxm 0.0087 Ohm WRIGHT inductance model
Exm 0.64 WRIGHT inductance model
Cmes 247 µF electrical capacitance representing moving mass
Lces 55.06 mH electrical inductance representing driver compliance
Res 56.6 Ohm resistance due to mechanical losses
fs 43.2 Hz driver resonance frequency
f ct 55.3 Hz driver resonance frequency in enclosure
Mechanical Parameters
(using test encl.)
Mms 15.657 g mechanical mass of driver diaphragm assembly including air load and voice coil
Mmd (Sd) 13.634 g mechanical mass of voice coil and diaphragm without air load
Rms 1.121 kg/s mechanical resistance of  total-driver losses
Cms 0.868 mm/N mechanical compliance of driver suspension
Kms 1.15 N/mm mechanical stiffness of driver suspension
Bl 7.966 N/A force factor (Bl product)
Loss factors
Qtp 0.399 total Q-factor considering all losses
Qms 3.789 mechanical Q-factor of driver in free air considering Rms only
Qes 0.388 electrical Q-factor of driver in free air considering Re only
Qts 0.352 total Q-factor considering Re and Rms only
Other Parameters
Vas 26.6853 l equivalent air volume of suspension
n0 0.533 % reference efficiency (2 pi-radiation using Re)
Lm 89.46 dB characteristic sound pressure level (SPL at 1m for 1W @ Re)
Lnom Zn missing dB nominal sensitivity (SPL at 1m for 1W @ Zn)
rmse Z 4.53 % root-mean-square fitting error of driver impedance Z(f)
Sd 147.41 cm² diaphragm area 


Klippel Large Signal Analysis

Fairly broad  Bl curve which shows a constant motor force with xmin/xmax (in/out).  Coil out offset at rest which trends toward the center of the magnetic gap at xmech with only a 0.30 inset.


Coil out offset which increases from 0.8mm at rest to 1.6mm at xmech.  As you’ll see below, this is what limits the linear excursion (10% THD) for this driver and as a result, Bl related excursion is not able to resolve.


The coil in offset makes it hard to tell from this plot, but it’s possible a shorting ring was used in this driver.


From this chart, it is easy to see that inductance isn’t a contributing factor in distortion for the low frequency evaluation of the motor.  Both Bl and Kms are contributing fairly evenly.


Displacement Limits thresholds can be changed in Processing property page
X Bl @ Bl min=82% >6.0 mm Displacement limit due to force factor variation
X C @ C min=75% 3 mm Displacement limit due to compliance variation
X L @ Z max=10 % >6.0 mm Displacement limit due to inductance variation
X d @ d2=10% 28.4 mm Displacement limit due to IM distortion (Doppler)
Asymmetry (IEC 62458)
Ak 82.83 % Stiffness asymmetry Ak(Xpeak)
Xsym -0.31 mm Symmetry point of Bl(x) at maximal excursion


As you can see from above, suspension was the limiting factor for linear excursion, limiting this driver to 3mm.  Not really what I would consider stellar by any means.


Frequency Response and Harmonic Distortion at 2.83v/1m

Good up until about 3khz in all measured axes.  A potential mode at 4khz (as indicated by the same peak in response in all axes).  Overall low distortion at this measurement distance/level to about 4khz where the THD breaks 1% (PHD level of -40dB).

3rd order distortion appears to be an issue at the 1-2khz range at this level.  But, as you see below, when pushed harder, 2nd order takes over and 3rd order remains relatively low.

High Output Harmonic Distortion

Very low 3rd order distortion from 100hz up to about 1khz where it increases slightly.  Very slightly.

2nd order distortion is the main culprit of distortion here and shows signs of concern centered about 900hz and 4khz.  On the low end, 2nd order still dominates, however, 3rd order starts rapidly increasing above 80hz.  At about 68hz, THD is above 3% and 3rd itself is above 3% at 60hz.

IMD Voice Sweep

Overall distortion results show an increase in distortion above 3khz.  So, like with FR, I wouldn’t necessarily recommend using this driver above that.  No matter, as polar response matching wouldn’t yield good results above this frequency anyway.

At its worst, this driver gives up about 0.70dB to compression at 4khz where the mode appears to be.  Overall there’s about 0.30dB lost to compression in the main passband up to about 3khz.



IMD (Bass Sweep)

Third harmonic takes over below 60hz.

At 90hz, compression results in a loss about 0.40dB.

One thought on “Seas W18NX-001

  1. Great review as always. I’m curious as to how similar / different the Lotus Reference would be to this driver.

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