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How Car Speakers Work

Simply, speakers are air pistons that move back (on the negative cycle of an electrical signal) and forth (on the positive cycle) creating different degrees of air pressure. These movements translate into different frequencies that translate into Mozart or Metallica at your eardrum.

To do this, an amplifier produces electrical impulses that alternate from positive to negative voltages and create an electromagnet when they reach the "voice coil" (a spool of wire) inside the speaker. This electromagnet will then either be repelled or attracted by the fixed magnet at the bottom of every speaker. The voice coil is attached to the speaker cone, and it moves the speaker cone back and forth as it's attracted or repelled. The surround (a rubbery circle that joins top of the cone and speaker's metal basket) and the spider (a circle of corrugated material that joins bottom of cone to the speaker's magnet) make the cone return to its original position. All this moving around makes "sound."

Speaking of Speakers

Coaxial speakers (or "three-ways") are two (or more) speakers built into the same frame.

Advantages
They can be inexpensive and are usually easy to install, often fitting into factory speaker locations without cutting or major modification to the car. Because coaxial woofers and tweeters are housed in one frame, you're assured good imaging.
Disadvantages
They lack the positioning flexibility of separate components, and with many models you can't aim the tweeter toward your listening position. Better speakers have two-way crossovers that filter bass out of the tweeter and treble out of the woofer so that each part of the system is playing the frequency range it can do best. Most coaxials come with simple crossovers that only filter the bass out of the tweeter but allow the woofer to run unfiltered (full-range) and that's a bad thing. Polk's db Series coaxials are unusual in that they have two-way crossovers for better sound.

Separates, or components, are sets of separate woofers and tweeters with an external crossover.

Advantages
More placement/system flexibility, and a better crossover. Best sound quality.
Disadvantages
Placement flexibility means you'll be drilling holes in your car to put separates in custom locations. You may be able to mount the woofer in the place vacated by your factory speaker, but you'll still need to make a separate hole for the tweeter. (The most common place to install tweeters is in the top front corner of the door panel.)

Subwoofers add the lower frequencies to a whole system. We could have a whole section on subwoofers alone. In fact, here comes one now:

Subwoofer Knowledge (or, The Sub is Greater than the Parts)

Some things are just true. The sun rises and sets. Christmas comes every year. Subwoofers need power. They need more power than anything else in your system. This is simply because they are bigger, and need more power to move their cones farther than other types of speakers. If you have an amp supplying 50W to each of your four front and rear speakers, you can bet on needing at least 100W for your sub(s). And you need to use a low-pass crossover to block the high frequencies from getting to your subwoofer and messing up the mix.

Low frequency signals reproduced by subwoofers are "non-directional." That is, it's most difficult for humans to tell where lower frequencies are coming from. So you can (theoretically) put a subwoofer anywhere without worrying about a loss of sound quality due to poor aiming and direction.

To make bass response more effective, subwoofers must be housed in a subwoofer enclosure. That would be a box. With a subwoofer in it. Because of this, subwoofers are most often placed in a car's trunk. A subwoofer enclosure can be simple ("sealed"), or complex (bandpass, that's pretty complex). Each kind of enclosure has its own characteristics, and the "one size fits all" rule of stretch denim and baseball caps does not apply here.

Ask us (go ahead, ask us), and we'll say that bigger is better. But-honestly-a good quality, well-enclosed 8" will outperform a cheap 12" sub any day. Big, cheap subs have slower responses and can sometimes be "boomy," while smaller subs tend toward a tighter sound. A bigger sub also needs a bigger box in which to enclose it. And if you fill up your trunk with a giant sub box, how are you going to haul the bodies (not to mention golf clubs!)? If you're going to go "big," don't skimp. Do it right. Check out our "Enclos-R-ama" for the basics of sub enclosures.

This article was last modified Aug 28, 2014

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