In reality, this is very similar to a sealed enclosure, except that the enclosure is extremely large and doesn’t affect the frequency response of the speaker. This type of design doesn’t work with SUVs or hatchbacks since they don’t have a trunk to capture the sound from the back of the subwoofer cone. The sound coming from the rear is trapped in the trunk. Your installer will either cut a hole in the rear deck of your sedan or mount a subwoofer on a board behind the rear seat so that you hear only the music coming from the front of the speaker. That’s exactly what happens in an infinite baffle subwoofer installation. The simplest solution is to create a wall or baffle that keeps these sound sources separate.
We need to separate those two sound sources from each other for us to hear bass information. Understanding that the sound coming off the back of the subwoofer (or speaker) cone cancels the sound coming from the front is the first step in comprehending why a subwoofer needs an enclosure. Signals that are equal in amplitude and frequency, but opposite in polarity, will cancel each other out. When they are added together, they cancel each other out, and you get the green line. In the graph below, you can see two sine waves, one in yellow and another with opposite polarity in blue. As the cone moves forward, the pressurized air in front of the cone is canceled by the rarefied air behind the cone, and vice versa. If you were to take a subwoofer out of its carton, connect it to an amplifier and play music, it wouldn’t make any bass. In all cases, the enclosure has two specific purposes that are crucial to ensuring that your subwoofer sounds excellent. Many enthusiasts have debated the benefits and drawbacks of acoustic suspension (sealed), bass-reflex (vented), bandpass and infinite baffle designs in hopes of choosing the best solution for their application and expectations. Most of us have heard of many types of car audio subwoofer enclosures.