User manual JBL GT1241D

[. . . ] Warning: Playing loud music in an automobile can permanently damage your hearing as well as hinder your ability to hear traffic. We recommend listening at low levels while driving. JBL accepts no liability for hearing loss, bodily injury or property damage resulting from use or misuse of this product. Choosing an Enclosure GT Series subwoofers are optimized to perform best in small sealed, vented and prefabricated bandpass enclosures. [. . . ] Vented enclosures are also well suited to a variety of music types. Because vented enclosures require the volume of the enclosure and the size of the port to have a specific relationship with the characteristics of the woofer, the enclosure must be built exactly to the specifications provided. While there are some prefabricated vented boxes available, matching a prefabricated box to a particular woofer is difficult. If you wish to use a vented enclosure, we strongly recommend having your authorized JBL dealer build it, or verify that your design is correct if you wish to build it yourself. An optimum vented enclosure is always larger than the optimum sealed box for the same woofer, and will require more space inside the vehicle. Bandpass enclosures often provide the most output available from any amplifier-and-subwoofer combination at the expense of sonic accuracy. If sheer SPL (sound-pressure level) is what you desire most, choose a bandpass enclosure. Bandpass-enclosure design is very tricky; using a computer and enclosure-design software is necessary. If you are an experienced installer or have some woodworking experience, you may wish to build the enclosure described in the Specifications chart in this manual. Fortunately, there are many prefabricated bandpass boxes available, and they are all optimized to extract the most output possible from any woofer. Bandpass enclosures can be quite large and may require a lot of space inside your vehicle. 02 Connecting Your Subwoofer to Your Amplifier JBL GT Series subwoofers are available in three different configurations: single 4-ohm voice coil, single 8-ohm voice coil and dual 4-ohm voice coils. Depending on the amplifier you are using, you may use either single- or dual-voice-coil subwoofers in singles or multiples to maximize the power available from your amplifier. To achieve the maximum amplifier output possible, you should design a speaker system that provides the lowest impedance that your amplifier is rated to drive safely. When designing a subwoofer system, abide by the following rules: 1. [. . . ] The total system impedance of woofers in parallel = 1/(1/w1 + 1/w2 + 1/w3. . . ) where w is the nominal impedance of the woofer. The total system impedance of voice coils (or woofers) in series = w1 + w2 + w3. . . The diagrams below and at right show parallel and series speaker connections. [. . . ]