Drivers ListSundown Audio DriversZV4 18d2

ManufactureSundown Audio
Motor TypeOverhung
Driver Size18 "
Driver Weight70 lbs
Coil Diameter3 "
Coil MaterialAL
Coil Length2.441 "
Gap Height1.1811 "
Manufacture's Xmax35 mm
Geometric Xmax16 mm

TS Parameters (Measured by

Fs24.9 Hz
Res3.4 Ω
Le 1khz4 mH
Sd0.115 m2
Vas180.8 liters
Mms417.6 grams
Cms98 μm/N
BL22.26 Tm
BL2/Res145.8 N2/W
L/R Time Constant1.18 milliseconds
SplSens89.78 dB


This 18” from Sundown is a hefty 65-70lb driver with an xmax rating of 35mm and a xmech rating of 50mm one way. It carries a street price of about $650.The driver utilizes a huge surround which was a recently tooled piece by Sundown in order to offer increased linearity of the suspension at extreme excursions on their higher end drivers. The surround is 51mm wide and extends a bit over 40mm above the frame. It is said to support 100mm peak to peak excursions without issue and to maintain a very linear compliance curve through the first 60 to 70mm of peak to peak stroke. Since the surround is so big it does eat into the cone area a bit and based on measurements leaves this 18” driver with an SD of about 1140cm using the typical half surround method and about 1050cm using the 1/3rd surround method used here at Data-Bass. The surround is glued as normal but is also double stitched to the cone to help prevent separation when the driver is being worked hard. The huge surround also makes putting a grille over this driver or utilizing it inside of a horn enclosure somewhat challenging because the surround already protrudes 40mm above the frame which is greatly increased when the cone is pushed to 50mm of outward stroke. This driver is primarily targeted at the mobile audio market so most users likely would not implement a grille over the driver to begin with though. The rest of the suspension system consists of a pair of large 10” diameter spiders with a set of heavy gauge leads sewn into them. The suspension components used allow tons of stroke without danger of stretching tight or quickly tightening the compliance.

The frame used for this driver is the common 6 spoke pattern which has been painted gloss black and has a large aluminum spacer ring applied which allow it to fit the extra wide 10” spiders and also provide a bit of extra mechanical clearance for large coil incursions. It comes with the usual wrap around rubber gasket too. The terminals used are a heavy duty set of spring terminals that allow very heavy gauge wire to be inserted. The driver cone is a very steeply raked heavy paper pulp cone which is weatherized on the front and is topped off with a small dust-cap adorned with the Sundown logo. At the bottom of the frame where it attaches to the motor is a 10mm aluminum spacer ring with large vent holes that allows heat to escape from the top of the gap and also provides further mechanical clearance on the in stroke of the driver.

 The dual voice coil used for the ZV4 is a 3” nominal diameter, aluminum flat wind with an 8 layer thickness and a wind of about 62mm height. The former is also aluminum. There is both a dual 1 ohm and dual 2 ohm version available. The motor is a about 8.75” in diameter and uses a triple stack of 25mm thick magnets. The top plate is very thick at about 30mm high while the back plate is about 20mm thick with a 10mm deep bump out for clearing the voice coil during large incursions. The motor has a T-pole vent that is chamfered and about 25mm in width. There are also 6 large vent underneath of the gap to also vent hot air out of the motor. Other features of this motor are an extended pole piece with an aluminum pole cap and also an inner magnet shorting ring, also of aluminum, that are used to help linearize inductance effects with stroke and help keep inductance related distortion down. The motor is capped off with a rubber magnet boot for protecting the magnets which has the Sundown logo on it. Running the small signal driver parameters showed that it has an RE of about 3.4 ohms with the voice coils wired in series and an FS of 25Hz after a bit of break in. The MMS came in at around 418 grams but it is likely a bit higher in reality. The BL came in at 22.261 which while not extreme is enough for this driver to perform well in sealed enclosure and vented enclosures that will barely fit the driver and or vents required. The 1kHz inductance for this driver was almost 4mH exactly. Judging from this and the complex impedance values and the shape of the impedance curve above 100Hz it indicates that this driver will still exhibit some inductance effects despite the shorting rings in the motor. This is not surprising with a driver with this much voice coil and steel in the motor.

Running a 20Hz sine wave through the driver while it was clamped to the test bench revealed that it is very quiet and linear through the first 2” of peak to peak excursion. At about 3”  of peak to peak excursion it is  moving a lot of air through the vents and the motor and is starting to make a lot of air noise and some mechanical clatter. The driver was pushed right up to the point where the cone was very close to touching the spider landing and leads where they transition into the spiders which looked to be about 3.5” peak to peak or 45mm one way. At this point the driver was very loud making lots of mechanical and air noise. All extremely long stroke drivers exhibit these noises in free air as it is simply too much mechanical action and air movement to not make some noise and the actual bass from the driver is cancelled out. Once the driver is put into an enclosure, which allows the output to not be cancelled out by the back-wave and also buries the motor inside the box, these noises typically become moot until the driver is really over driven. This driver appears to have an xmech of about 50mm where the cone will contact the spider landing or leads. The smaller driver sizes have a newly tooled frame which has greater clearances so the xmech on those is actually a bit higher. The 18” basket was not available yet at this time.

Overall this driver appears to be suited to dishing out boat loads of deep bass more than head cracking upper bass and as such really seems to lend itself to a sealed enclosure where the extra excursion capability can allow it to be pushed a bit harder than most other drivers without fear of bottoming it. It can also work in other types of enclosures just fine but getting large enough vents on it could be problematic and it has so much excursion potential that it will take a huge amplifier to get everything out of it in a reflex enclosure above the vent tune with tunings at 25Hz or higher. Either way it is capable of doing some damage and has the linearity to also sound good if employed right.


Sundown Audio 18" ZV4 18d2 Systems