Drivers ListBMS Drivers18N862 8ohm

ManufactureBMS
Motor TypeOverhung
Driver Size18 "
Driver Weight23.2 lbs
Coil Diameter4 "
Coil MaterialCU
Coil Length1.9685 "
Gap Height0.47244 "
Manufacture's Xmax19 mm
Geometric Xmax19 mm
Aprox. Price$800 USD
Year2012

TS Parameters (Measured by Data-Bass.com)

Qts0.357
Qes0.383
Qms5.23
Fs29.1 Hz
Res5.5 Ω
Le 1khz1 mH
Sd0.1219 m2
Vas242.6 liters
Mms255.2 grams
Cms117 μm/N
BL25.89 Tm
BL2/Res121.9 N2/W
L/R Time Constant0.18 milliseconds
SplSens93.78 dB

Notes

BMS is a German pro audio manufacturer and the 18N862 is one of their top of the line 18" drivers. This is an expensive long stroke pro audio 18 subwoofer built on a proprietary 8 spoke cast aluminum frame with under spider venting, heat sinking, a cork front gasket and a neodymium magnet overhung motor. The motor has what appears to be a 3 or 3.5"x 0.5" thick neodymium ring magnet with a 1.5" inner hole through which the pole vents. The steel case is moderate size and has the previously mentioned large flared pole vent plus 12 smaller under gap vents. The coil is a long 4" diameter sandwiched copper wind. Additionally the motor contains triple aluminum demodulating rings to keep distortion very low and linearize inductance. Due to the big voice coil and extensive venting power handling is rated at 1500w program via AES protocol and the geometric xmax is a generous 19mm due to the long 50mm voice coil wind and a 12mm top plate height. The suspension consists of a large 3 roll coated accordian type cloth surround and what appears to be a double set of 8" diameter nomex progressive spiders. The cone is double treated carbon fiber impregnated paper that is very light weight. Indeed the moving mass on this driver is very low for a 4" coil long throw 18 at only 260 grams or so. The terminals and leads are a bit unusual and are a single set of heavy duty spring terminals which are mounted against what appears to be a piece of circuit board that the very heavy gauge leads are soldered to. Overall build quality is very good. Despite all of this hardware this is a very light driver that weighs in at just over 23lbs. rn

rnThis driver is a little odd in a few ways. Instead of the very stiff suspension and high FS that you would usually see with most pro drives this one has a very light moving assembly a good 100 to 150 grams lighter than most comparable units and a high compliance suspension that moves freely with little effort. This results in a lowish FS of about 25-29Hz instead of the usual 33-40Hz. Also the motor is plenty strong to control the assembly but compared to a lot of other pro super woofers the BL2/RE product is only about 120. The extremely light moving assembly, triple shorting rings in the motor and high compliance suspension help to keep the sensitivity up though. The linear xmax is quite a bit longer than all but a few other "pro" style drivers like the TC 5100 and the IPAL drivers. The xmech seems to be generous as well. But after asking BMS directly what the xmech and/or mechanical clearances of the driver were because they are not listed, I was told it was 22mm on two occasions. I even asked the tech representative if they were sure and this was not the Xsus rating or something. After all the driver has an actual geometric overhang of 19mm implying it can travel at least that far with ease. 3mm of mechanical clearance past that point would be plain old bad design and asking for broken drivers. Also considering the 12mm gap height with the 19mm overhang that implies that the motor is probably capable of making the coil travel at least 31mm in one direction before running completely out of force. Assuming that the suspension can stretch that far of course. Anyway despite BMS's assertion that the xmech is 22mm on this driver and the 860 version as well I clearly drove it well past that mark in free air testing with no ill effects. The motor appears to have plenty of rearward clearance as does the triple joint to top plate distance and the suspension did not seem to be stretched tight when driven to about 50mm peak to peak. All of that plus the design credentials of BMS point to the xmech being something more like 35mm or so. This seems far more realistic for this driver design. Excursion up to about 1.5" peak to peak is relatively quiet but the motor starts to make some air noise past there as well as the suspension developing notable noise. Useful excursion is rather large for a sound reinforcement style woofer.rn

rnParameter testing and impedance measurements show that the inductance is very well controlled which is not surprising due to the triple shorting rings in the neo motor. Combined with the light moving mass this gives the 18N862 a very nice top end which should be useful up till at least 500Hz. It would make a great woofer for a large three way. Additionally the very light weight of only 23 lbs is refreshing and a good 20 to 30 lbs lighter than other woofers with comparable power handling and displacement. I worry about the cone of this driver handling high power horn loading though as it is very lightweight and not as robust as many other drivers so I would hesitate to recommend it for high pressure high power cabs with potential uneven pressures acting on the cone. Less cone strength is the typical trade off for a lighter moving mass and better sensitivity. This should be a great bass reflex woofer or even sealed woofer though as it behaves as a blend between a typical long throw HiFi type sub woofer and a high power pro woofer.

BMS 18" 18N862 8ohm Systems