Drivers ListRockford Fosgate DriversT3S2-19

ManufactureRockford Fosgate
Motor TypeOverhung
Driver Size18 "
Driver Weight70 lbs
Coil Diameter5 "
Coil MaterialAL
Coil Length3.15 "
Gap Height0.472 "
Manufacture's Xmax34 mm
Geometric Xmax34 mm
MSRP$2499 USD
Year2015

TS Parameters (Measured by Data-Bass.com)

Qts0.256
Qes0.305
Qms1.6
Fs23.5 Hz
Res1.7 Ω
Le 1khz1.1 mH
Sd0.1472 m2
Vas133 liters
Mms1043.3 grams
Cms44 μm/N
BL29.28 Tm
BL2/Res504.3 N2/W
L/R Time Constant0.65 milliseconds
SplSens89.36 dB

Notes

This is Rockford Fosgate’s top of the T3 or “Power” line, the largest and most powerful bass driver they have ever made, by far…They call it a “superwoofer”. You’ll get no argument with that here. With a suggested retail of $2499 it had better be. It is called a 19” driver and based on cone area it is. However the surround is very wide and so is the flange on the frame so the actual total frame diameter is a full 21”. A cutout to recess this driver needs to be about 21.125” for a nice snug fit. This driver has a much different design from most and as such looks a bit unconventional. It was shown complete at CES and with an internal cutaway also. As soon as the shots of the cutaway driver were seen it was clear what was going on with the motor and overall driver design and the search for one to test began.

The T3 19” driver design is very heavy on engineering and performance verification and appears to use very little, if anything, that is not tooled specifically for this platform. The size is not standard as previously mentioned. The diameter of the frame and cone area place it somewhere in between a typical 18 and 21 driver size. Something like a 19” as they call it is about right. The build starts with a proprietary, very heavy duty cast aluminum frame, which is actually 2 pieces that bolt together. It has 6 very thick spokes and two gigantic spider landings which are spaced nearly 2.5” apart. The spider landing placement is far below the surround as well so this driver should have better than normal lateral stability, which will be needed as we will discuss later. As mentioned the mounting flange is much wider than normal at about 21” total diameter but a cutout for the driver is about 17.6”. This gives a lot of area for the driver to seal. The 8 bolt mounting pattern is around 20” diameter and the driver ships with 2 sets of very nice allen head wood screws. The screw holes will accept large screws or bolts as 1/4x20 bolts will easily fit with some room to spare. There is a gasket built into the mounting flange close to the spokes. The outer rim of the mounting flange is very thick and is machined and polished which gives a bit of flash to the side profile. The flange actually extends quite a bit under the surround and has a chamfer on the edge on the inside. The cone on this driver is a large 3 layer sandwich composed of glass fiber/ Aramid honeycomb/ glass fiber. It also has a substantial amount of “rake” towards the top spider and the back side includes a reinforcement neck where the former meets the cone. The dust cap is a large aluminum cap with a polished trim ring and the Rockford Fosgate logo. The cone is very stiff and strong. A couple of these drivers did exhibit a few areas on the front of the cone where the “weave” was not perfect but they were minor detail spots. The aluminum dust cap seems to be quite thick and sturdy but like most thin metals it will dent if something is dropped on it or it is pushed on too hard. This was found out the hard way unfortunately when a large area of the dust cap was unintentionally pushed in on one of the drivers. Luckily a bit of Gorilla tape pressed onto the dent and slowly pulled out popped the dent right out and that driver cannot be visually distinguished from a few of its brothers afterwards. One driver out of the 9 that are on hand did have a dust cap which was slightly turned and did not line up well with the mounting holes like the others. This in no way affects the performance but it is an annoying quality oversight on a driver as expensive as this one.

The suspension design on this driver consists of a very large, very tall and wide surround which clearly has the clearances for big excursions. The surround system and profile is something that RF has developed and calls VAST in their literature. The surround material is an injection molded foam which does feel more like rubber than foam. It is quite thick and very stiff. There is also a mechanical clamping system on the surround but figuring out how that works or where it attaches has been elusive. It may be up under the surround inside of the frame. The surround protrudes very high above the frame. In fact it is nearly 2.5” from the top of the surround to the bottom of the mounting flange. On a few of the drivers received there are a few small imperfections on the surrounds where the injection molding can be seen as a slight variation on the surround color in one area, which is likely where material cooled a bit differently than the rest during the material injection. This also doesn’t affect the performance but on a driver this expensive purchasers may find any imperfection to be an issue. The rest of the suspension is the pair of spaced, single layer (very thick) Nomex spiders which were said to be specifically built for this driver. They are a progressive design, a full 12” in diameter and are incredibly stiff but like the surround they clearly will allow extreme amounts of movement. The leads are sewn into the top spider and have a ton of slack and feature a rubber jacket. The leads are very supple and flexible. Much more so than normal. There is a single set of terminals which are integrated into the frame with what appears to be a bolt on sub assembly. They are a pair of color coded, spring loaded terminals, which are deeply recessed and will accept huge 4ga wire. The bare minimum should probably be 10ga or equivalent. 12ga can become loose. During free air testing with quite a bit of power, this happened and caused an arcing effect with a blue spark shooting out of the negative terminal, which burnt up a bit of the speaker wire where there was little contact area with the terminal. Luckily both the driver and amplifier took it in stride. Double runs of 10ga or equivalent to about a 7ga single cable is what will be used on these after that experience. Interestingly the leads are run on both sides of the former but there is only one set of terminals on the driver. I suspect that this is where the second set of terminals would have gone but they were removed from the design due to the coil arrangement. Still doesn’t make sense to have a dummy set of leads going nowhere. It is entirely possible that something is being missed on my part but I suspect it is something where it was easier to just leave this in after the design was changed.

The motor design on this driver is a bit different. It appears to be a giant version of a Differential Drive motor (JBL terminology though there are at least 2 more previous patent holders with variations.) Basically stated there are two separate gaps with two voice coils each operating in their own gap. The coils can be wound in opposing polarity, as they are in this driver, which helps improve linearity and also dramatically reduces the inductance. The dual gaps also generate a lot of motor force on the coil. With a typical single gap motor the only gap in the circuit is by the top plate where a typical coil sits and the bottom plate is solid and just carries the flux as part of the magnetic circuit. In this type of design the bottom plate also has a gap in the circuit and another coil is placed in that gap. Of course you end up with a much longer former and deeper driver as a tradeoff. However in this type of system the coils can be made to magnetically brake the excursion or incursion of the moving assembly once the “opposing” coil reaches the other coils gap or flux since its direction is reversed. In that case, if enough clearances are provided elsewhere in the driver moving parts, the driver becomes basically impossible to mechanically bottom. The T3 19 uses this type of system. In the case of the T3 19 the design utilizes a large diameter top and bottom plate, each around 12mm thick, forming the two gaps in the circuit. These are spaced around 100mm apart. The magnets are arrayed in 6 columns evenly spaced between the two plates. The magnet column assemblies are likely 2 chunks of neodymium of unknown grade one at the top plate and one at the bottom, both with a center hole, and a steel cylinder with threads or a center hole between them. There is said to be 115oz of neodymium magnet used in this driver. Around these components is likely to be an aluminum tube to hold everything in alignment. These are then aligned and bolted to the top and bottom plates through the center of the column assemblies. The pole piece is likely to be a single large chunk of steel, perhaps shaped, perhaps with shorting rings, that is suspended evenly by the 2 gaps to complete the circuit. An aluminum frame structure which the gap plates and top assembly and frame bolt to, holds all of these components centered and immobile. The motor frame has 6 spokes which are ribbed like a heat sink and which feature vertical slits which travel all of the way up into what would normally be the pole piece area and presumably bolt to the steel core forming the motor pole at some point. It may also act like a Faraday ring in the motor as well depending on the inner geometry and proximity to the coils. This whole motor assembly bolts to the top assembly and frame with 12 bolts. It appears to be a simple removal which is planned at some future point, but the typical sizes of tools do not seem to fit. The voice coils for this driver are in a word mammoth. They are a 5” nominal diameter and are single layer aluminum edge winds using the largest gauge wire I’ve personally seen on a voice coil. Additionally the winding height is about 80mm or 3.15” for each coil with about a 12mm gap separating them. This is a huge amount of coil mass. The coils are coated with a dark gray coating that has been becoming more popular with drivers having extreme power handling. The former the coils are wound on is a 5” diameter aluminum piece which also seems to be a bit thicker than normal. The former is very long since it has to attach way up at the cone and the bottom of the second coil. That about wraps up the design of the driver. Everything is oversized and seems to be made for durability. What you end up with is a 70lb neodymium based driver which would probably be pushing 180lbs if built using ferrite magnets. It looks unconventional to say the least and a byproduct of the large clearances, spaced spiders and double gaps is a driver that is roughly 18” tall from the back of the frame to the top of the surround. The mounting depth is listed at 15.64”.

The T3S2-19 driver was broken in for a bit in free air with a 25Hz sine wave which should be near the impedance maximum of the driver which would keep the power low. Afterwards the parameters were pulled. This quickly became interesting. Usually the drivers are clamped to the test stand by the motor but in this case the motor frame tapers steeply the entire way and made this impossible much like with the Aurasound NS18. The test stand is not setup to clamp by the frame either since the frame is much weaker and easier to warp than the motor typically and also a much larger diameter. Initial measurements of this driver and the Aura NS18 which was being done at the same time both showed issues in the impedance curve capture indicating vibration induced noise and variation. The T3 was much worse than the NS18 since the moving mass is much greater. The compromise was sitting the driver on sand bags and then stacking a number of other sand bags and a 50lb weight on top of the driver frame. There is still some noise and general fuzziness in the impedance captures but the close match to the RF factory specs confirmed that it was good enough to get the job done. Re, Sensitivity, 1kHz Le and the measured SD were all extremely close to the factory specs. The effective SD for this driver is 1472cm which slots it right between a typical 21 and 18” drivers cone area. The Fs came in a bit lower than factory at 23.5Hz versus 27Hz. Long term break in will likely drop that a bit more. The suspension stiffness measured a rock hard 44um which again is close to the spec calculated using the factory parameters. The only other driver that has been measured with a stiffer suspension than this is the B&C 21IPAL. Interestingly these drivers also have the two strongest motors of anything tested thus far. At least part of the reason for the super stiff suspension becomes clear when we look at the moving mass of the T3 19. 1000g! It’s not really surprising that with a triple layer sandwich cone, heavy surround, incredibly long aluminum former, a pair of gigantic 5” voice coils and two 12” diameter spiders the moving mass is substantial but the T3 19 has by far the heaviest moving assembly that has been encountered yet. This is actually very close to the RF spec once it is derived. The suspension needs to be very stiff to combat sag and alignment issues with a former that long and so much weight. The other wow factor that jumps out of the parameters is the normalized motor force based on the BL and resistance of the coil. It is just over 500 which is exceptional. A normal “strong” motor for an 18” driver would be in the 200-250 range. This helps combat the heavy moving mass and keep the efficiency relatively high. This is also very close to the RF factory specs that can be backed out of their listed parameters. The Qts and Qes are slightly different but that is mostly due to the slightly different suspension stiffness and lower Fs more than anything. The static 1khz inductance comes in slightly higher at 1.1mh but an L/R time constant of 0.65ms places this among the lower inductance bass drivers despite the huge aluminum voice coils. After roughly measuring a few things on the driver the one way xmax rating appears to be based on the simple coil overhang which is right at 34mm. combined with the top plate thickness and some other rough measurements done it appears that the driver will start running out of motor force and magnetically braking in the other gap field at about 45mm one way give or take a mm or two. Just to be clear this does not sound good when it happens. It sounds like very sharp and nasty clipping which in a way it is just that. However instead of something smashing into another part or tearing as you would have on a more standard bass driver in this case it mostly just makes a very nasty sound, though you do not want to drive it that hard very often. The mechanical limit on excursion seems to be about 54mm or so based on a very rough measurement and seems to be limited at the triple joint of the bottom spider on the former and the top of the motor. The clearance at the cone to spider landing and former to back of the aluminum motor frame both were a bit greater. However it does not appear that the moving assembly can be driven to that point anyway. The T3 driver was surprisingly quiet in operation until driven to large excursions. Due to the moving mass of this driver and the excursion it is capable of which approaches 3.5” peak to peak, it shakes whatever it is mounted to more forcefully than a lighter weight driver. Be careful when using it in smaller, lighter enclosures or in vehicles. Dual opposed makes a lot of sense for cancelling this effect although it could be put to use when intentionally coupled to a riser or seating. RF rates the power handling of this driver as 3000 watts rms and 6000 watts peak. Power handling ratings are notoriously inflated and over emphasized but this drivers power handling is surely above the norm. The sheer amount of material mass in the dual 5” winds and the amount of aluminum directly near the pole piece and the 6 cooling channels in it should help as would the heavy gauge aluminum former which also has vents above the top gap. The motor itself is very open with most of the coil surface directly exposed to the air and air movement over it in operation. Rockford Fosgate is also conforming to the CEA-2031 standard for rating power handling in mobile electronics speakers. This standard is different from the old AES ratings used by the professional sound community but it IS a standard and does have guidelines so it is a step forward for the car audio brands if it starts to become widely adopted. Rockford Fosgate and at least 3 other of the major car audio brands are now using it so that is encouraging. Rockford Fosgate also uses Klippel systems for the development and measurement of their drivers now. The T3 19 is Klippel verified and it shows in the engineering and performance of the driver. Measurements of this driver show that it offers huge amounts of displacement, smooth frequency response up past 150Hz, very low distortion even when being driven hard and the ability to cope with very large amounts of power as expected. The normalized motor force of 500 means that this driver could be used in very small boxes that will barely contain it. The efficiency is decent but it is squelched quite a bit by the 1000g moving mass. Interestingly without equalization this driver sounds like a pro audio woofer in typical enclosures. The RF T3-19 is an exotic statement driver and as such is very expensive but the result is a very high performance bass driver indeed.

Rockford Fosgate 18" T3S2-19 Systems