You're walking down the street and you begin to hear a low rumbling that gets louder and louder until it almost feels like the sidewalk is going to break to pieces! Are you in an earthquake? Is an airplane about to smash into your little section of the sidewalk? Are aliens about to suck you up into their invisible spaceship?

As exciting as that would be the sad answer is no, its just your neighbor Jimmy. He 's on his way home from the car audio installation shop and he just a got a big fat subwoofer speaker.

Now you've probably heard this term before but maybe you're not sure about what subwoofers actually are and how in the world they can pump out terrifyingly loud and low sounds. If this is the case then let me explain.

What is a Subwoofer Speaker?

A subwoofer is a loudspeaker just like any other with one main distinction. They are built and optimized for low frequency sounds. Typically they are dedicated to producing frequencies anywhere from 15Hz to 100Hz IE frequencies that will make you feel like you're exploding.

Sound is produced when a pattern or pressure is sent through a medium like air or water. Any time you make a sound or noise you're creating a pattern of pressure that is sent out through the medium you're in, usually air. Clap your hands and you're creating a short pressure pattern thats distributed throughout the space around you.

Hz stands for “Hertz”. You've probably heard the term mega or giga “hertz” for computers before. Maybe yours has a CPU that runs at 2 gigahertz. Anyway just trying to build some mental connections to the word :) Hertz can be defined simply as cycles per second. The higher the pitch of the sound you hear or make the higher the frequency. Have you ever heard a Tuba play a really really low note? You can usually hear  a beating pattern in it. That's the pressure pattern at work. Its much harder to the pattern for higher pitched because the pressure pattern is so compact and close together.

So when a subwoofer plays a note that has a frequency of 25 Hz that means the pressure pattern is repeating itself 25 times per second. Now that may seem like a lot but when compared to other higher frequencies its really nothing at all. Some of the highest audible frequencies are in the 15,000 to 20,000 Hz range.

So to bring us back to subwoofer speakers, subwoofers again are dedicated to producing those low frequencies with clarity and precision. There are some speakers that are called full-range speakers but these are less popular simply because they lose sound quality in the more extreme ranges. You could call these speakers “jacks of all frequencies, masters of none”. They are good for small spaces but if you want true clarity and precision then you need to diversify your speakers sets. Subwoofers are the manifestation of someone creating a speaker to master the bass frequencies.

In conjunction with the actual subwoofer speakers are amplifiers that are specialized for subwoofers. Amps as they're usually called do just that, they take the wattage coming into them, amplify it and then send it on to the loudspeaker. Subwoofer amps are also built with specific components that filter out frequencies that aren't supposed to be there. They limit the frequency range to meet the specifications of the actual speaker to preserve fidelity and improve sound quality by minimizing distortion that can be caused by a speaker over stepping its bounds and limits.

Another great thing about subwoofer is that they have no directional needs. Other, higher range speakers need to be carefully placed, being directed at the listening position to achieve the best listening experience possible. However subwoofer have a lot more freedom of movement and placement because their low frequencies don't need to be directed in any one direction get great quality. This is why you can hear Jimmy from miles away and think the universe is imploding.

Next time you hear that ominous rumbling instead of going for the bomb shelter take a look down the street first. Most likely its just Jimmy coming home from work :)