The subject of this month's review, the new JL18W3 18" subwoofer, is certainly no exception. Like all of JL's products, the W3 series is rather feature laden. The 18" W3 subwoofer is built on a heavy custom stamped metal frame with substantial rear excursion distance (47 mm) for the spider provided by both the frame's construction and by a vented spider standoff. The cone assembly consists of a stiff mineral filled polypropylene cone with a 6.5" hard poly convex dustcap (silk-screened with the JL logo), foam surround and cloth type spider. The cone has a unique flat edge for attaching the surround and also adds stiffness to the outside diameter of the cone. The surround is fairly large, about 1.25" wide and 0.75" high, and is intended to accommodate the long excursion capability of the voice coil. The foam used in JLs surrounds is referred to as "double-density" which the company maintains provides superior lateral stability compared to rubber and Santoprene type surrounds. Providing the rest of the compliance is a large 8" diameter flat progressive roll spider ("progressive" refers to the spiders ability to decrease its compliance as excursion increases). The mounting platform for the spider is vented, adding to the airflow across the forward area of the voice coil.
One of the most interesting technical features, besides some neat tricks in the motor system, is JLs patented VRC, a clever mounting platform that provides an improved mechanical joint for the critical glue bond between the cone, spider and voice coil, as mentioned earlier. If your woofer comes apart here, you're out of business. Not only does this high temperature plastic collar provide increased surface area for an improved mechanical joint (as well as strengthening this area so it doesn't lose its shape on long hard excursions), but it also provides vent tunnels that force air across the voice coil for additional cooling. The 18W3 (and the 15" version, the 15W3) uses a modified version of this system called VRC+. This combines the VRC system plus JLs own patented type of peripheral venting. The pole piece on the 18W3 is not only vented down the center, but also has a series of 12 lateral vents positioned just above the vent area. Located in this manner causes the vents to push copious amounts of air into the area of the voice coil that gets the hottest, the top area that rides outside the gap. Taken all together, this driver has four systems designed to increase air flow across the voice coil for increased thermal stability: a vented spider platform; the venting in the VRC; the center pole venting; and the lateral pole venting. This is a very well-conceived thermal system.
Powering all of this is an equally well-conceived motor system. JL Audio employs about as sophisticated engineering technology as any of the companies in the subwoofer business. This means they employ not only F.E.A. (Finite Element Analysis) CAD software for magnetic, thermal and mechanical design of woofers, but also have developed over a period of time simulation software written internally. All of this comes into play with the design of the motor structure, which for the JL 18W3 includes using dual-stacked magnets, each 122 mm in diameter and 22 mm in height. A brightly polished forged T-yoke and 11mm front plate conduct the magnetic field and focus it into the gap area. The pole structure part of the T-yoke includes the 12 lateral vents and an 11/16" diameter center vent that are an integral part of the VRC+ system. This structure includes a 9/16" height bumpout ("Powerbump" in JL speak) to accommodate long rearward excursions. With a substantial BL of 20.3 TM (measured with the two coils in series), the motor structure drives a 2.5" diameter 4-layer dual-winding voice coil wound on a Kapton former. Each winding is 1.67 ohms, or 3.35 ohms when connected in series (as I did when I measured the parameters of the JL 18W3).
T/S parameters were measured using the LinearX LMS analyzer and the new LMS4 Windows software (a big improvement over the original DOS version) and LEAP CAD software. Impedance was made using a LinearX VIBox (current source method), which means that the analyzer was connected directly to an amplifier driving the woofer. Rather than creating a single impedance curve, the procedure produces separate voltage and current curves at a 1V drive level that are divided (V/I=Z), using the LMS post processing menu. Once the free-air and test box impedance curves were created, the two curves were transferred to the LEAP program to calculate the T/S parameters. The resulting parameters and computer box simulation data are given in the Data Chart with the LEAP sealed/vented box simulation graph shown in Figure 1.
The measured parameters shown in the Data Chart were used to produce two different box simulations, a 3 cubic ft. sealed box with no fill material and a 4.75 cubic ft. vented box tuned to 26 Hz. Both box sizes are recommended by JL in their literature, but many other combinations are possible. With a Qts in the vicinity of 0.4, this driver could be made to work in almost any style box, but I tend to think that the best and most compact would be the 3 cubic ft. sealed box, which produces an F3 of 43 Hz with a moderately damped box "Q" (Qtc) of about 0.78. This was with no fill material.
If you fill the box with 50% R-19 type fiberglass, the Qtc drops to 0.72. While the lower Qtc also means more excursion, this really isn't a problem for the JL 18W3. The maximum linear operating level was 118.8 dB where the driver reached its maximum linear excursion limit of Xmax + 15% (14.7 mm), but was reaching a voice coil temperature that indicates that this woofer is more likely to be thermally limited than excursion limited. However, given the extent of the cooling system in this monster woofer, I definitely wouldn't want my ears, or yours, in the car when you finally heated it up sufficiently to fail. This is a very powerful device and should be treated with respect.
The vented box is larger and of course plays lower in frequency with an F3 of 29.6 Hz. It also takes more power to push it to its excursion limits. At 68V the simulation predicts 122.1 dB. As can be seen in the LEAP graph, damping changes appreciably at these voltage levels (LEAP uses non-linear models of BL and compliance plus dynamic changes in voice coil temperature to simulate this with a good degree of accuracy), but that's normal. This also explains why the smaller sealed box is probably more musical at almost any level as the changes in dynamic damping aren't as radical as it is with a vented design. Either way, your ears will be distorting before the JL 18W3.
Considering the outstanding performance and reputation for reliability that comes from JL Audio plus the enhanced thermal cooling capability, this new JL 18W3 woofer should be a hit with anyone who's got the space to use it. How does it sound with music? I think Mikey likes it. --V.D.
Listening
This no-nonsense woofer has a look that says "strictly business." The design is all about function without flash. What you are paying for here is top-notch performance. Connections are handled with a pair of 0.187" faston terminals on each side of the basket, one set for each of the 2-ohm voice coils. I took advantage of these connectors and soldered the incoming wires for the lowest resistance, which you can't do with spring-loaded terminals. A tall gasket on top of the basket allows for inverted mounting, or even isobaric loading (two woofers in a push-pull configuration) without worrying about the surrounds colliding.
I used a sealed cabinet with a volume of 3.82 cubic ft., just under the manufacturer's recommended maximum size of 4 cubic ft.. This yielded a Qts of 0.762 according to LMS. The enclosure was built of 3/4" plywood with braces across the center to prevent the panels from resonating. No damping material was added.
I connected the two voice coils to the stereo outputs of an amp that produces 500 watts per channel into a 2-ohm load. The speaker is rated for 400 watts continuous power, leaving me with a decent amount of headroom for transients. I measured the maximum SPL output of this single driver at 125.8 dB, SPL, in the minivan. I set the crossover point to 100 Hz for the listening tests.
The first thing that came to mind when I began to listen was the word "smooth." No matter the type of music I played or the volume level, the woofer seemed to stand there with its arms crossed saying, "When are you going to give me a challenge?" It has excellent linearity, with no discernable difference between very low and very high volumes. On the title track of Radiohead's "Kid A" disc, there is a synthesized kick drum sound that has a very fast attack and decay which is great for checking for overhang. This speaker was more than fast enough to handle it with ease.
If you want accuracy and detail in combination with the ability to generate massive SPL, I doubt you will find a better choice than this. You will need a large box volume to take full advantage of the capability this 18 provides, but it's well worth it.