Enclosure Construction, Dual Coil Versus

ENCLOSURE

CONSTRUCTION

Please observe the following suggestions when building an enclosure for GTi

4. Fill the enclosure with damping

material (Dacron,® ﬁberglass insulation

or long-ﬁber wool) according to the

design you have chosen from the

DUAL COIL VERSUS

DIFFERENTIAL DRIVE®* Conventional dual-voice-coil woofers use a pair of voice coils “interwound” on

Figure 2. Conventional dual-voice-coil design

CONE

Series subwoofers.

1. Choose an enclosure design from the

Enclosure Design Sheet included with

your subwoofer.

2. Use at least 3/4" (19mm) MDF (medium

Enclosure Design Sheet. “0% ﬁll”

indicates that no damping material

should be used; “50% ﬁll” indicates

that all interior walls except the bafﬂe

should be lined with 1"-thick damping

the former and centered in the magnetic gap. The two coils may be connected in series or parallel in order to maximize an ampliﬁer’s output power. Both coils drive the cone forward and rearward. Xmax

BOTH COILS DRIVE CONE FORWARD AND REARWARD

SPIDER

OVERHANG DETERMINES

Xmax

TOP PLATE

density ﬁberboard) or marine birch

plywood to build the enclosure.

Enclosures for 12" and larger sub-

woofers and smaller woofers driven

by high-power ampliﬁers should be

constructed using 1" (25mm) material.

3. Join pieces of wood with glue and

screws; do not use nails. Once the box

has been tested, seal all joints inside

the box with silicone caulk.

material, and “100% ﬁll” indicates that

the box should be loosely stuffed with

damping material.

5. Use PVC or ABS plastic pipe for ports.

Keep in mind that the openings at

either end of the port must be at least

one port diameter away from any

obstruction.

6. Use the 10/24" machine screws and

T-nuts provided to mount the woofer

to the bafﬂe. See Figure 1.

Figure 1. Mounting the GTi woofer in its enclosure

(one-way-linear) is determined by the amount of voice coil exposed above and below the top plate. A conventional voice coil is made up of several layers of windings, each transferring heat to the winding next to it until the heat is ﬁnally dissipated by the outside layer through the top plate, magnet and backplate. This arrangement is inefﬁcient, and results in low thermal power handling. See Figure 2.

MAGNET

POLEPIECE / BACKPLATE

JBL GTi Series subwoofers employ Differential Drive, a technology developed by JBL Professional. Differential Drive employs two voice coils positioned at opposite ends of the former, each suspended in a separate magnetic gap. These two coils may be connected in series or parallel, like a conventional DVC woofer, to maximize an ampliﬁer’s output power. Both coils MUST be connected to the ampliﬁer in correct polarity! At low power, both voice coils drive the woofer’s cone, and any motor nonlinearities are cancelled by the out-of-phase coils and gaps. As

10/24"

SCREWS (PROVIDED)

power input increases so that one coil rides completely out of its gap, force is still applied to the cone by the other coil.

T-NUTS

(PROVIDED)

* U.S. patent no. 5,748,760 and other patents pending

MkII automotive, MkII W10GTi, MkII W15GTi, MkII W12GTi specifications

JBL, a leader in audio technology, has long been synonymous with high-performance sound systems. Among its stellar offerings are the MkII series subwoofers, including the W12GTi, W15GTi, and W10GTi. These subwoofers represent a fusion of superior engineering, innovative technology, and durable construction, making them ideal for automotive enthusiasts seeking to enhance their sound experience on the road.

The JBL MkII W12GTi boasts a 12-inch cone driver, designed for deep and powerful bass response. It's constructed with a patented dual voice coil to provide effective power handling while minimizing distortion. This subwoofer features JBL’s signature GTi technology, which includes a high-temperature voice coil to ensure longevity and performance under heavy usage. Its sleek design includes a rigid aluminum frame that helps reduce unwanted vibrations, enhancing sound clarity and precision.

Meanwhile, the MkII W15GTi, with its larger 15-inch driver, takes bass amplification to another level. The W15GTi is engineered for even deeper low-frequency output, making it perfect for genres that rely heavily on bass. It incorporates advanced cooling technology to dissipate heat effectively, allowing for extended playtime without compromising performance. Additionally, its robust construction ensures resilience to the demanding conditions of automotive use.

For those who prefer a more compact solution without compromising sound quality, the MkII W10GTi serves as an excellent choice. Featuring a 10-inch driver, this subwoofer is versatile and delivers impressive bass response even in smaller systems. The W10GTi utilizes a unique cone design to enhance sound dispersion, ensuring that every note is heard clearly. Its tight construction optimizes the management of air within the enclosure, further improving acoustic performance.

All three models in the MkII line share essential technologies, such as JBL’s patented Slipstream ports, which reduce port noise and enhance airflow, leading to cleaner bass output. Additionally, they feature adjustable frequency response, allowing users to customize their listening experience according to personal preferences and vehicle acoustics.

In summary, the JBL MkII W12GTi, W15GTi, and W10GTi subwoofers are exceptional products for automotive sound systems. Their advanced technologies, impressive power handling capabilities, and robust designs make them ideal choices for audiophiles and casual listeners alike, setting a new standard in mobile audio performance. Whether you’re looking for deep rumbling bass or a balanced audio output, JBL’s MkII series delivers unparalleled value and performance for the modern car audio enthusiast.