Loaded subwoofer enclosures come in Passive or Active styles. Passive enclosures, or boxes, require an additional amplifier to produce sound while Active enclosures have amplifiers built into them and are self contained all-in-one systems.
Subwoofer drivers, also know as subs, are specific only to the lowest frequencies of the sound spectrum, and are the largest drivers in any car stereo. They are generally found in sizes of 8″ – 12″ diameters. Subs move massive amounts of air creating large pressure waves. These large pressure waves give that bottom end punch you expect from your kick drum, the undeniable funk of a bass guitar and the earthshaking bump of a house beat.
The frequency range of a subwoofer generally covers the first 2 octaves of the sound spectrum, also known as the lows. Subwoofers require their own mounting structure called a sub box. Sub boxes are built to create negative pressure on the sub to help move their large diameter cones back and forth for accurate reproduction of low end frequencies. Custom subwoofer boxes are built to meet certain cubic air space specifications of sub drivers and are sometimes custom built to fit under seats or other hidden areas to maximize the use of space in the vehicle. JL Audio’s Stealthbox's are custom designed to fit many vehicles while minimizing the footprint needed to be installed in your car.
RMS vs. MAX power: The RMS rating of any speaker driver is the continuous power rating that the speaker is designed to withstand at a maximum continued volume rating. The RMS rating is the only number to go by when pairing your speakers with an amplifier. As an example a speaker with a 100Watt, or 100W for short, RMS rating and a 300-Watt Max rating is ultimately a 100 Watt speaker. The Max rating is the temporary spikes in voltage that the speaker can handle. A 100-Watt RMS / 300-Watt Max speaker is going to outperform a 100W RMS / 250W Max speaker at higher volumes, but may not be the more detailed reference speaker.
Ohms: The Ohm rating, or resistance rating, of a speaker is an essential part of a well balanced car stereo system. Many JBL factory speaker systems have 2ohm drivers. Most aftermarket speakers are 4ohm drivers. Replacing these types of factory speakers may require a wiring bypass of the factory amplifier.
Driver resistance ratings are essential when pairing subwoofer and speaker drivers with amplifiers. An amplifier that is 750W @ 2ohms might only generally be 500W or less @ 4ohms. When purchasing a subwoofer driver the correct pairing of a subwoofer’s RMS wattage and Ohm ratings with an amplifier’s output power rating is absolutely essential.
Frequency Response: Frequencies are measured in Hertz or Hz for short. The frequency response of speaker drivers will generally fall between 20Hz and 22kHz. At 20Hz the sound spectrum begins. Every time you double your frequency you move up one octave in scale. 20-Hertz to 40-Hertz covers the first Octave, 40Hz to 80Hz covers the next octave and so on. Subwoofer drivers are generally tuned to crossover at 80 Hertz. This can depend on the subwoofer type and the type of music you listen to.