If you desire to increase the loudness of your existing subwoofers, there are many low- as well as higher-cost options available to you. It is extremely important to have a quality amplifier that will make full use of your existing subwoofer system's power capabilities. Having the proper size and type of subwoofer enclosure will also play an important factor when it comes to squeezing out every bit of potential your subwoofers have. It is also important that the connections to your amplifier are properly done while using a wiring kit recommended by the manufacturer to ensure peak performance.
Check the wiring configuration as it relates to the subwoofer connections to your amplifier. If your amplifier is “bridgeable,” wire the speaker leads together in parallel (the negative speaker wires twisted together, as well as the positive speaker leads twisted or connected together). "Bridging the amplifier" simply means combining both the left and right channels together to form a more powerful monaural channel; check with your amplifier’s documentation to find out which speaker terminals to use for bridging (certain brands may call for you to utilize the left channel positive terminal and the right channel negative, while others may require the use of the left negative and right positive).
Consult your amplifier’s manual with regard to adjusting the gain, frequency crossover and bass boost controls. Initially, you should set your gain and bass boost controls to the minimum setting, turn the volume up on your stereo before the point of audible distortion from your high-range speakers and then gradually increase the gain control/bass boost settings before audible distortion occurs from the subwoofers.
Check to make sure you are using the appropriate size and type of enclosure for your subwoofers. The specification sheet that came with your subwoofers will provide you with the recommended type and size of enclosure that will enable you to get the most out of your system. If you already have the recommended type and size of enclosure for your subwoofers, try facing the subwoofers at a different angle by turning the enclosure around either facing away or toward the listening position in the vehicle (this may help direct/reflect the low frequencies toward you by making better use of the natural acoustics of the vehicle).
