Drivers List18Sound Drivers21LW1400

Motor TypeOverhung
Driver Size21 "
Driver Weight42.4 lbs
Coil Diameter4 "
Coil MaterialCU
Manufacture's Xmax9.5 mm

TS Parameters (Measured by

Fs20.3 Hz
Res5 Ω
Le 1khz2.56 mH
Sd0.1662 m2
Vas705.3 liters
Mms334.5 grams
Cms183 μm/N
BL36.54 Tm
BL2/Res267 N2/W
L/R Time Constant0.51 milliseconds
SplSens97.53 dB


This Italian made 21” woofer is 18 Sound’s most cost effective unit of that size and has some strong performance characteristics. It is built on a large proprietary cast aluminum frame with an open design with plenty of spider venting. The motor is a large double stacked ferrite magnet driven design with an OD of slightly over 8.5”. The back plate is generously bumped to clear the 4” diameter copper voice coil during high excursion and also features a large, roughly 2” diameter, pole vent with a screen to prevent debris from entering the gap. The voice coil uses an inside outside wind which is becoming increasingly popular with high end pro-sound woofers. 18Sound calls this ISV (Interleaved Sandwich Voicecoil).

The motor is also listed as having two demodulating rings to control inductance but there is no mention of whether they are aluminum or copper. The cone is listed as a pressed paper pulp impregnated with carbon fiber having a number of reinforcement ribs. The suspension consists of dual spiders of about 8” diameter and a large 3 roll accordion type surround. The high compliance of the suspension on this driver indicated that it was well broken in and was surprising since most pro woofers typically have rather stiff suspensions. This resulted in an unusually low FS of about 20.5Hz compared with 18Sounds spec of 28Hz. The moving mass of this woofer is very low for a long throw 21” driver at a little over 300grams and this coupled with the very high amount of BL from the motor resulted in a very low Q and a lot of efficiency --even greater than 18Sound specifications list. The only drawback with low mms is that it usually means a very light cone and in the case of this 21” it seems reasonably durable but compared with heavier cones found on car audio drivers it is notably more fragile. Protection of the cone is recommended.

The LE results and impedance curve indicate that this driver has well controlled inductance due to the double shorting rings no doubt and has cleanly extended upper bass response. At less than 43 lbs this driver doesn’t weigh much more than some smaller drivers with neodymium based motors. The SD is listed at 1662cm but a measurement using 1/3rd of the surround put it right at 1600cm which is only a 4% difference. 18sound lists this drivers linear mathematical xmax as only 9.5mm and Xmech at 52mm peak to peak. This is one of the few drivers that overachieves in this regard and performs in a manner that indicates that useful excursion is somewhat more generous than that spec would indicate. During free air testing 1” peak to peak excursions were notably quiet and noise free. At about 1.5” peak to peak the suspension starts to complain and at 1.75” peak to peak testing was limited due to getting close to the Xmech spec and the fact that the driver was complaining loudly at that point. Still given that this driver is only listed at 9.5mm xmax and that is remains linear enough to be useful at about 17 or 18mm almost double the rating is impressive. Many drivers with claims of substantially more xmax and with more total stroke do not operate nearly as quietly. At high excursion there is a lot air movement in the motor pole vent and from under the frame but it did not offer a lot of noise.

As usual this pro style driver will not best the super long xmax drivers for under 30Hz bass output but it has strengths that make a lot more sense if that reproduction is of less concern. With the street price on this driver it appears to be a solid option for a variety of high output situations.

18Sound 21" 21LW1400 Systems