Systems ListJTR SpeakersCaptivator 2400-ULF

ManufactureJTR Speakers
System typeVented
Driver Size18 "
Number of drivers1
External volume10.94 ft3
Dimentions (Width Height Depth)41 " 20.5 " 22.5 "
Weight165 lbs
Native Tuning Frequency10 Hz
Power2400 W


Here we are beginning test season for 2018 with another JTR Speakers subwoofer. This time the subject is the Captivator 2400-ULF. Following the success of the powerful and HUGE Captivator 4000-ULF, which was Data-Bass tested a while back, it is a logical progression to saw the dual driver 4000 in half and make a smaller, lighter and less expensive little brother for the Captivator subwoofer lineup. That is exactly what we have in the Captivator 2400-ULF. 

This particular subwoofer is available in 2 different cabinet configurations. One is very deep but narrow and short. The other is the version tested, which is tall but narrow and less deep. The 2400-ULF cabinet is constructed of high grade baltic birch ply like the rest of the JTR speaker line and comes with the same lightly textured, durable black finish as the other JTR subs as standard. Other custom finishes can be provided for an up-charge. The cabinet is internally braced, lined with damping material and features a thin profile, front mounted, slot port and driver. The outer dimensions are 41x20.5x22.5 which works out to almost exactly half of the size of the 4000-ULF. The vent tuning likewise is said to be at the same frequency as the 4000-ULF, which is an unusually low 10Hz.  

The 2400-ULF houses a single heavy duty 18" driver built on the cast aluminum TI style frame, with a large half roll surround and very large diameter spider for linearity at high excursion. The voice coil is a 3" diameter. The cone is a heavy pressed paper body with a carbon fiber dust cap. The power handling on the driver is obviously quite high judging by the amplifier pairing and the performance during testing. Xmax is quoted as 33mm one way with xmech coming in around 40mm. It appears to be the same driver as used in the big brother 4000-ULF subwoofer. The amplifier is sourced from Speakerpower and is the 2400 watt rated version of the Torpedo series with DSP and limiting that has been tailored to the JTR application. The overall weight of the subwoofer is 165lbs and it carries a cost of $2599 plus shipping direct from JTR. 

During testing and use the 2400-ULF was exemplary. It has a large amount of headroom, a smooth yet flexible response shape and low amounts of deep bass distortion. Additionally the 2400-ULF seems to be pretty much bulletproof. It never really gets into too bad of shape no matter how hard it is driven. The amplifier seems to give out a bit before the driver can make any truly offensive noises. The cabinet is very inert as well and exhibited no rattles or buzzing issues. You might find yourself hitting the amp limiter, but may not notice, because the sub doesn't let out any obvious, out of place, overdrive noises like some others. Some vent noise artifacts were about the worst noise it will make, but this is only when driving it very hard down below 14Hz . This is unlikely to occur very often. Pretty much every vented sub will make some air noise when driven hard near the vent tuning, but the extra low tuning on this sub means that most content will be well above the vent tune and content that truly tests the sub near the tuning should be pretty rare. 

The Cap 2400-ULF offers real, effective 10Hz extension from a vented sub design and one that is a finished turn-key design with a warranty and support to boot. This type of extension and headroom combination is very rare and used to only be available to DIYers willing to roll the dice and fabricate their own solution. Most commercial commercial options are tuned nearly an entire octave higher and for good reason. It is not as easy as tuning any old driver and cabinet to the lowest frequency possible. Keeping the cabinet size, vent area, vent length and pipe resonance reasonable is a juggling act. Additionally by tuning lower, higher frequency efficiency and output are traded off. It takes a lot of raw air displacement to produce good headroom over the entire operational bandwidth and on down to the very lowest frequencies, which require more from the driver or drivers. It is not an easy set of compromises to balance. These and many other points are why this type of design are extremely rare. Hats off to Jeff for getting it right on his Captivator ULF subwoofers. 

As expected the 2400-ULF performs almost exactly like a half of the 4000-ULF. Another comparison worth looking at is the Captivator 1400.