Feed your ears

The Kenwood 6969ie three-way bass speakers are suggested for use with the Kenwood KAC-8401 amplifier.

There’s a big difference between base level specifications for truck cab sound systems and premium systems, says Tom Puza, chief engineer for audio systems at Delphi Corp. He should know. Delphi designs and provides lots of base systems for truck manufacturers.

Premium systems may have six, eight or as many as 12 speakers, plus an amplifier to adequately supply them. Because they are composed of high-quality components that are perfectly matched and ideally located, premium systems are difficult to improve upon.

While normally by no means deficient, the base system, typically with only four speakers, is designed with attention to cost. Much can be done to improve it without spending wildly or tearing valuable components out of the truck.

The audio heads (radio, CD player, satellite radio receiver, or tape deck) installed in trucks are usually of good quality, Puza says. For that reason, plus the fact that what really matters to your ears is the speaker output, a good starting point for upgrading a sound system is the speakers. Common improvements can focus on three factors: the speakers’ quality, location or type of covering.

What accounts for speaker quality? Something called “sensitivity” or “response.” Better speakers have a higher sensitivity number, so you’ll get more sound for the same amount of power. Sensitivity is often marked in decibels (dB) on the speaker box. Better speakers tend to have a better balance among bass, mid-range, and tweeter (higher) tones output, too.

There are many aftermarket speakers that will upgrade typical original equipment, says Steve Conner, Delphi’s manager of audio and acoustics. If you’re not changing the amp, choose a speaker of the same wattage rating but higher dB, assuming you can find all those specs. But, he says, “If your present speaker efficiency is not marked and it was installed by someone else, you may be shooting in the dark.” In that case, an expert at an audio dealer could listen to your system and suggest possible improvements.

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As for optimal locations, Delphi experts recommend that the primary speakers be up front, right and left. The addition of rear speakers creates the sensation of sound all around you.

Inadequacies attributed to speakers often originate in the covering, in which case they can be easily fixed. The cover “must not cover any part of the speaker cone, or you’ll lose and distort the sound because it will block certain parts of the sound spectrum,” Conner says. “Many rattles and buzzes get blamed on the speakers when they are actually trim- and mounting-related.”

He says there are grill cloths and other covers that are “acoustically transparent. If there’s a metal grille, you should be able to see through it easily so the sound will have a good chance to get through.” If you’re installing a new speaker, the safest approach is to choose a speaker case and grill designed for the particular speaker.

Another upgrade is adding an amplifier between the audio head and speakers. Puza says upgrade components are available at most audio shops.

The amp not only gives greater power and control over the sound signals, but it allows you to add speakers. A typical upgrade with an amp is to expand a four-speaker base system into an eight-speaker system, which can make quite a difference in a truck. “A vehicle has a lot of rumble and noise. This can be hard to overcome, and doing so takes a lot of power,” Conner says.

Furthermore, “A lot of trucks lack deep bass sound output,” he says. The goal is to “move more air, and a bass speaker with a bigger diameter than the original speakers will do the trick.” The simplest way to do this is to install a subwoofer box and amp combination unit. The original audio head will then drive the original four speakers, and the separate amp will drive the new low-frequency (subwoofer) speaker, getting only its signal from the original audio head.

One option to installing a powerful amp is to replace the audio head with one that provides more power and is of better quality, says Dave Campbell, a sales advisor for Crutchfield, a major retailer of vehicular sound systems.

Wiring becomes a major challenge if you want to replace the audio head because you need to identify the wires in the factory harness. Campbell says a good audio system installer can identify all the wires using electrical instruments, simplifying installation. He estimates that a radio that would be a clear step up from a base level truck system could cost as much as $800.

For the most cost-effective solution to a problem of low power, he says, “I would just add an amp, but would pay someone to do the job.” The goal is to create “enough quality sound to overcome all that ambient noise.” A four-channel amplifier, preferably with output of at least 50 watts per channel, costs $100 to $300.

Campbell says the best overall approach is a component system. This would include two sizes of speakers in a common box and a crossover. The crossover separates the tweeter sounds from the mid-range sounds.

The component system would include two such two-speaker units consisting of 6.5-inch mid-range drivers (producing frequencies in the range of the human voice), with separate tweeters. You’d add two 6-inch-by-9-inch bass speakers mounted in boxes. The component system might range from $150 to $300, while the speakers would likely cost $100 to $300.

One reason you need three types of speakers is that a given unit can handle only sounds within a certain range of frequencies. For example, feeding too much bass to tweeters can break them. Also, directing impulses to the proper speaker helps produce a more distinct sound.

Readily available components can turn your noisy cab, with its so-so sound system, into a state-of-the-art listening room. If you’re not up for a do-it-yourself project, an audio shop can perform the upgrade and have you back on the road in a matter of hours.

In a typical sound system upgrade, the first step is that the speaker wires from the original radio that run through the factory wiring harness will be disconnected at the speakers and capped off. The original radio will still provide the signal.

The installer will tap into eight spare outputs on the radio and run 20-gauge wires to the new amp. Wiring the supply to the new amp this way will effectively bypass the radio’s less powerful amplifier and supply just the signal that’s needed to the new amp.

The new amp must be mounted vertically, possibly on a wall, says Dave Campbell of Crutchfield, because it has a heat sink to remove heat generated by current flow. If the device’s fins sit vertically, natural air circulation cools it more effectively, extending its life. It will be grounded via a bolt.

Next, 16-gauge wire will be used to conduct impulses from the new amp to the speakers. Separate wires will run directly to the bass speakers. The wires for mid-range and tweeter sounds, however, will run to the two-way crossover network of the component system.

Frequencies over 3,500 Hz go to the tweeters, while those lower go to the mid-drivers. Additional 16-gauge wiring that’s part of the component system will shunt the electronic impulses over to the two two-speaker units that come with it.

Finally, the bass speakers in truck boxes will be mounted behind the seats. The component system speakers that include the tweeters will be mounted on the roof so the sound is actually aimed right at your ears when you drive. This puts you in what Campbell describes as a “sweet spot,” where the high-frequency sounds will be telegraphed right to your ears rather than being altered as they bounce off the cab interior.

Delphi Corp. experts say a capable do-it-yourselfer might be able to handle such a job. They recommend asking specialists where you’re buying about how difficult the job might be. Crutchfield offers tech support on its toll-free phone line.

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