Years ago, an EQ booster was a standard part of any car audio enthusiast’s arsenal. Back before high-power amplifiers became available, an under-dash EQ booster served the dual purpose of adding a bit of extra power to a system and providing a crude means of adjusting the overall sound. But EQ boosters couldn’t produce any more power than an in-dash receiver and their signal processing capabilities were very limited compared to today’s high-tech equalizers, so they’ve fallen out of favor with most enthusiasts.
One school of thought that believes that if a car audio system is designed and installed properly, there’s no need for an equalizer or processor. After all, no amount of equalization can compensate for a system that’s poorly designed and installed. Instead, use of an equalizer or processor should be thought of as seasoning to a well-prepared meal and therefore used sparingly. An equalizer is designed to fine-tune a system and make small corrections, not compensate for problems caused by poor design or improper installation.
Divide and equalizer
By now, you’re probably wondering exactly what it is that an equalizer equalizes. Every sound you hear, including music, is part of the audible frequency range, which for humans is roughly from 20 Hz to 22,000 Hz. Below 20 Hz, you don’t so much hear sounds as feel them, which is why low bass has such as visceral, body-massaging quality. Above 22,000 Hz are sounds that only animals such as dogs can hear, which explains why those silent dog whistles work. Very few adults can actually hear sounds around 20,000 Hz anyway because high- frequency hearing quickly degrades with age.
A perfect car audio system would produce the entire frequency range with a flat, or even, response from 20 Hz to 22,000 Hz, with no deviation. But audio equipment and particularly speakers are far from perfect. Maybe that’s a good thing because a flat frequency response sounds ... well, flat. After all, who doesn’t want to crank the bass a bit every now and then even if it’s not balanced perfectly with the rest of the system?
A relatively flat frequency response — one with an equal amplitude or signal strength across the audible frequency spectrum — is the ideal, but it does not define a good-sounding car audio system. Instead, it’s an ideal to shoot for, and an equalizer, which allows tweaking or adjusting the frequency response of a system far beyond the simple tone controls for bass and treble found on a head unit, lets you get closer to that ideal.
Equalizers do this by boosting (increasing) or cutting (decreasing) the gain or amplitude of an audio signal within a band (range) of frequencies. Equalizers may have several frequency bands that are fixed or unalterable, or may allow adjusting the center frequency, which is the primary frequency at which the adjustment takes place.
The segment of the audio spectrum that a frequency band covers, say 50 to 100 Hz, is known as the bandwidth. Related to bandwidth is an equalizer’s Q factor, which defines the way in which the range of frequencies within a band of control are affected. A smaller Q means a wider range of frequencies are affected by an adjustment of the equalizer, whereas a larger Q means a narrower range of frequencies are affected.
One more tech term you should be familiar with is octave. Octave is a musical term that refers to an interval between one musical note and another that’s half or double its frequency. So if 100 to 200 Hz is one octave, 200 to 400 Hz is another, and 400 to 800 Hz is the next. The most sophisticated equalizers are known as one-third octave because their bands are spaced one-third of an octave apart, as opposed to basic EQs that spread control over several octaves and allow less precise adjustments.
Types of equalization
Beyond where they’re mounted (in-dash or in a trunk), car audio equalizers are generally classified in one of three types:
Graphic: These types of equalizers have a set of fixed frequency bands fj over which adjustment is allowed (see Figure 17-1). The term graphic 1 relates to the fact that you can see a graphic representation of what the I equalization curve or response is supposed to look like because the sliders or controls on a graphic EQ are set in a way that mimics the amount of boost or cut at each center frequency.
Figure 17-1:
A dis-continued Pioneer graphic equalizer.
Parametric: Parametric equalizers (see Figure 17-2) allow adjustment not only within a certain frequency range, as with a graphic EQ, but also permit varying the center frequency at which the adjustment takes place. Some also allow varying the Q factor of the affected frequencies.
Quasi-parametric: These equalizers allow adjustment of the center frequencies but do not offer adjustment of the Q factor of an equalizer (see Figure 17-3).
Types of equalizers
Equalizers are also categorized by where in the vehicle they are usually placed: the dashboard or the car’s trunk.
Figure 17-2:
An Audio- Control parametric equalizer.
Courtesy of AudioControl
Figure 17-3:
A Kicker quasi- parametric in-dash equalizer.
In-dash equalizers
For years, most in-dash equalizers (see Figure 17-1) were graphic EQs and were basically the descendents of EQ boosters. (In other words, no serious car audiophile would be caught dead with one.) But many modern in-dash EQs are of the parametric variety and offer added-value features (see Figure 17-3), such as subwoofer crossovers (which allow adjusting the amount and character of bass via the amplifier that’s driving the subwoofer) and auxiliary inputs (that allow adding another audio source, such as an iPod). The biggest advantage of in-dash EQs is that they allow making adjustments on the fly.
Trunk-mount equalizers
These equalizers have their roots in the pro sound world, mixing for concerts and in recording studios. They are typically much more sophisticated than in¬ dash equalizers and allow more precise control over a system. They are also usually more expensive. Trunk-mount equalizers (see Figure 17-2) are usually one-third octave equalizers and are of the set it and forget variety. To adjust them properly usually requires an excellent ear or a device called a real-time analyzer (RTA) that measures sound, or both.
Some aftermarket and even factory car audio head units also have simple graphic equalizers built in. Although they can be helpful in tweaking a system, they are limited in their function and scope.
Signal processors
Car audio signal processors come in a wide variety of prices and offer a broad range of features (see Figure 17-4). Some do only one or two things (such as boost bass or increase the line-level or unamplified signal from a head unit so that the overall system has less noise), whereas others do everything from equalization to time alignment, which is delaying the signal going to certain speakers so that the sound from all the speakers in a system arrives at a listeners’ ears simultaneously.
Other functions you’ll find on car audio signal processors include
Surround-sound processing for movies and music
Sound-field processing that adds effects to recreate the sound of a certain space, such as a cathedral, concert hall, stadium, or jazz club
Crossover that sends certain frequencies to certain speakers
Additional inputs for adding auxiliary audio sources such as an iPod or other portable music player
Circuitry that enhances the sound of compressed-audio formats such as MP3
Figure 17-4:
A Pioneer in-dash signal processor.
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