Much unlike the mids and highs, subwoofers are made specifically to lower registers of sound. The lowest sound that a human being can hear is topped at 20 Hz. And, of course, there are many bass notes that are well above 40 Hz, so, you should not just look for a subwoofer that can play the lowest note and then just end it there.
This usually becomes more pertinent when you look at the mid-lows. The mid speakers are typically focused on playing vocals and other melodic frequencies of music. And because of this, some of the higher lows that are played in music can muddy a mid speaker’s sound. And that is why a subwoofer with a frequency range that is above 200 Hz can really improve the total sound quality of your audio system and it can be an important factor, this depends on the genre of music that you listen to on a regular basis.
Subwoofers typically come in a wide variety of sizes that are judged based on the diameter of their cone. Although modern inventions let smaller and smaller speakers cones to make comparable audio quality, volumes, and frequency ranges, there is still no way to get over the fact that the larger speakers are typically able to make a wider range of frequencies at a louder volume.
When it comes to subwoofers, the most common speaker sizes out there are 10 inches and 12 inches in diameter.
The impedance of a speaker is just a measure of its resistance to an electrical current. This resistance experienced is measured in ohms and mostly determines just how easily it can translate from a head unit or an amplifier into sound. A lower impedance usually will create a better quality of sound.
This happens so because the digital signal experiences less distortion through a less resisted set up.