Car Audio Glossary
‘A’ is for Amperes
A measure of electric current. How much is enough? (We like to say that having too much amperage is like having too much money.) Your car’s stock alternator probably provides enough amperage to power a basic car audio system. But if you want to add multiple high power amplifiers, you might require some additional current, and the installation of a new alternator or stiffening capacitors (see this link section with answers to your questions for more on alternators and stiffening capacitors). Ampere is commonly abbreviated as “amp” (not to be confused with amplifiers), but sometimes it’s “I.” Electricity is like that.
An electronic circuit that directs which frequencies go to which speakers. For example, since subwoofers are designed to best reproduce only the lowest frequencies, a subwoofer crossover (a low-pass crossover) allows only the low frequencies to pass through to the subwoofer. Freed from the task of reproducing heavy bass, your other speakers will rejoice by performing better and playing louder. You need crossovers so that you don’t send unnecessary signals to a speaker (which could damage it).
‘dB’ is for Decibel
A measurement of power ratios and volume levels. All you really need to know is that to gain 3dB in volume (a moderate increase in playing volume), you must double your available power. There. That’s it.
‘DC’ is Direct Current
A type of circuit. In a DC circuit, the current always flows in one direction. In your car, you’re dealing with a 12volt DC system (twelve volts of direct current). Hence the term, ‘12volt Guys.” In a car, it’s important to keep track of which wires are attached to the ground (or “negative”) lead of the battery.
“Hz’ is for hertz
A measure of frequency. One hertz is equal to “one cycle” per second. A cycle of sound is the duration between similar portions of a sound wave (between two peaks, for instance). Frequency can describe both electrical circuits and sound waves, and sometimes both. For example, if an electrical signal in a speaker circuit is going through one thousand cycles per second (1000Hz, or 1kHz), the speaker will resonate at 1kHz, producing a 1kHz sound wave. Got all that?
A description of the illusion of being able to locate certain sounds as “coming from” certain places. If you have a system with good imaging, the sound should seem to come from different distinct instruments and voices, not from speakers. A singer would generally be in front of you (center stage), and the band would be arranged around them. See also “staging.”
A measure of resistance and impedance that tells you how much a device (like a speaker) will resist the flow of current in a circuit. If the same exact signal is sent into two speakers, one rated at 4 ohms of impedance, the other at 8 ohms of impedance, twice as much current will flow through the 4 ohm speaker as the 8 ohm speaker. All things being equal, the 8 ohm speaker requires twice as much power to achieve the same volume level, since power is proportional to current. (See “dB.”)
Can your impedance be too low? Yes it can. It all depends on how well your amplifier can handle the increase in current flow that comes with lower impedance. The more current, the hotter your amp will get. An overheating amp is trouble. A good amp will simply shut down when trying to generate too much current. A poor quality amp will burn. Makes sure your amp can handle the impedance of your speakers.
Measured in dB, is how loud a speaker plays with a given amount of power going into it. Conveniently, the usual measuring stick is 1 Watt at 1 meter. A higher sensitivity rating means that the speaker will play louder using the same power as a speaker with a lower rating. So, should you always buy the speaker with the higher sensitivity rating? Not necessarily, because you’ll usually end up trading off some other aspect of system performance like bass response or power handling. Sometimes a lower sensitivity rating gives a speaker a better (flatter) frequency response. How you announce your intention to spend your paycheck building a car audio system is your sensitivity rating.
Trust Your Ears, not the Specs
Specs can tell you how a speaker will sound, but they can’t tell you what a speaker sounds like. Trust your ears. And if you don’t know what to listen for, trust someone with listening experience, like the professional in the showroom.
Like “imaging,” is a description of your system’s ability to “fool you” into thinking that everything (including bass) is right in front of you. Like on a stage (hence the term “staging”), the singer should (in general) be in the center, and the band should be located to the left and right. Good staging (and good imaging) are not easy to achieve in a car audio situation. One of the hardest aspects of staging is getting the illusion that the bass is coming from the front of the car, even though the woofers are in the back. You may have to experiment with speaker locations, directions, and crossover roll-off points. Cheat the bass by overlapping the frequencies played by your mids and subs so that your semi-directional mids actually “pull” the bass to the front. To do this, use a high-pass crossover to roll off your midbass drivers as low as you can (without getting distortion). Then set your sub’s low-pass crossovers at a slightly higher frequency. (See More About Crossovers) This will mix the bass coming from the front and rear, giving the illusion that the bass comes from the front. Adding a center channel improves staging as well, but that’s next week’s lesson.
‘THD’ is Total Harmonic Distortion
Or how much a device distorts a signal. These figures are usually given as percentages. THD figures below approximately 0.1% are inaudible, but like bad karma distortion adds up.
‘V’ is for Volts
The measure of “electric potential.” Think of volts as the pressure and current as the flow of all those electrons. If you have high pressure and plenty of flowing electrons that means lots of work can be done. Another word for work is Power!
‘W’ stands for Watts
Another measurement of electrical power. One watt is equal to one volt times one amp of energy per second. Don’t be mislead by wattage specifications. All things being equal, a good, expensive 50W amplifier will outperform a cheap, marginal 75W amp. Here’s why: In order to play even 3 decibels louder, an amp must double its power output. The difference between 50 and 75W output is so small, maybe a dB or so, that you probably won’t even be able to tell. The human ear just doesn’t pick that up. To actually double the apparent volume, you’d have to have a 10dB increase in level. Basically, you’re better off with a more expensive, more efficient, better-built lower wattage amp than with that “200 Watt” amp you picked up for $39.95 at the flea market.
This article was last modified Dec 8, 2013