JBL 4645C Single 18" (460mm) Subwoofer System

The JBL 4645C is a high quality subwoofer system, featuring an advanced technology 460 mm (18"), low-frequency transducer mounted in a direct radiator, bass-reflex enclosure for smooth response to the lowest audible frequencies. The 4645C is ideal for low-frequency augmentation of either analog or digital soundtracks in motion picture theaters and for general sound reinforcement applications.

The 2242H transducer utilizes the patented Vented Gap Cooling (VGC) process, which pumps air through the magnetic gap and directly over and around the voice coil, providing immediate heat transfer and a reduction in operating temperature. This increases power handling while reducing power compression. The 2242H utilizes a rugged 101 mm (4") diameter voice coil and incorporates a large motor structure with a pole piece that extends both above and below the top plate to improve gap flux symmetry and increase thermal conductivity. This magnet structure and the use of a voice coil with one-third more exposed area than in former designs, provides the 2242H with very effective heat sinking, enabling the system to carry an 800 watt continuous AES pink noise power rating.

The magnet structure and compliance allow for long peak-to-peak excursions without damage to the speaker. The pole piece incorporates a shorted copper ring while functioning as a shorted secondary turn, with the voice coil acting as the primary winding. The benefits are a reduction of third harmonic distortion from magnetic flux modulation and a reduced inductive component of the voice coil impedance, for improved transient response. Symmetrical Field Geometry (SFG) minimizes second harmonic distortion.

The enclosure is constructed of dense stock and is extensively braced on all panels. It has a net internal volume of 225 liters (8 cu. ft.) and is tuned to 25 Hz with a very large port to minimize port compression and to reduce distortion due to turbulent air flow.