Detroit's latest thing with souping up is in the hi-fi system. Acoustics joins aerodynamics in getting the designer's ear

If you still think of automotive hi-fi as an AM radio with an extension speaker mounted on the deck behind the rear seat, listen again. Today's rolling sound systems, with their four-channel FM, tape and compact-disc players, and computer-equalized speakers, can easily rival some of the best home component systems.

They can also be just as costly and complex. But while some of the biggest names in automotive hi-fi are the same names you might find on home systems, the carmakers themselves have begun providing some of the best units now available.

One example is Chrysler's new Infinity system. Until recently, car stereos used whatever speakers could be squeezed into the available space, whether in a door panel or on the rear deck. The Infinity system combines Chrysler's best radio/cassette player with a set of six speakers custom-designed by Infinity Systems Inc., a company known for its high-end home audio speakers.

The result is a system that comes as close as one can imagine to sitting in front of a living room sound system, all the time speeding along at 55 miles an hour.

``Automakers have come to the conclusion that a person who has good sound at home also wants the same experience in his automobile,'' says Neville Pack, Chrysler's chief of corporate products.

Indeed, the Big Three carmakers are engaged in a sort of Sound Wars, with each forming an alliance with a major audio equipment manufacturer.

Ford, for example, has teamed up with the well-known speaker manufacturer JBL.

General Motors' top models offer buyers Delco radios matched with speakers from Bose.

That the carmakers are even offering these high-end sound systems is a big turnaround from just five years ago, when an audiophile would usually have to turn to the aftermarket, to manufacturers such as Pioneer, Sony, or Concord.

As good as some of these aftermarket systems are, however, there is usually a problem achieving ``perfect'' sound.

As Mr. Pack notes, ``When it comes to sound, a two-door is not the same as a four-door or a station wagon. Even the type of upholstery can affect sound quality.''

Thus, the speakers on even the best aftermarket system have to be, almost by definition, a sound compromise. On the other hand, top-end original-equipment systems are, when properly designed, tailored to the specific automobile.

The Delco/Bose system, for example, differs from conventional car stereos because of its built-in equalization. Microprocessors divide the sound signals into individual frequency bands and boost or cut the signal in each band to compensate for the acoustic quirks one finds inside a car.

``It's truly an engineer's dream,'' says Amar G. Bose, the Bose company's founder. ``We know where the listeners will be sitting and the exact acoustics of the listening environment.''

These custom-engineered sound systems are not offered on every one of the Big Three car lines. And they carry a hefty premium, usually about $1,000, several times as much as basic AM/FM systems.

(The Big Three aren't the only ones custom-designing sound systems for their cars, incidentally. Porsche has engineered a new six-channel system for its 911 Turbo models which will carry a price tag of about $8,000.)

Despite the advantages of custom-tuned speaker systems like the Delco/Bose, they are not for eveyone.

``We don't plan to offer the Bose speakers on many of our car lines,'' says Michael Losh, general manager of GM's Pontiac Division.

Mr. Losh says that many of his customers prefer to have greater control over their sound systems by ordering auto hi-fis equipped with graphic equalizers - effectively high-tech tone controls - which are not available on the Delco/Bose line.

Meanwhile, no one is counting out the new top-end systems provided by the carmakers, or the audio systems available from outside suppliers.

Indeed, some of the latest technological innovations tend to make their debut on aftermarket units. More than a score of manufacturers already market auto sound systems with compact-disc players, something Detroit has just begun to offer.

In fact, Sony offers one trunk-mounted unit, retailing for about $1,000, which can be loaded with up to 10 CDs. The unit is then remotely controlled from the driver's seat.

At $1,260, the Nakamichi system features the same sort of cassette tape drive mechanism and electronic options previously found only on the best home units.

Despite such hefty premiums, top-end stereos are selling very, very well, whether they are built in or added as an aftermarket option.

While Chrysler is planning to install Infinity systems in 12 percent of its LeBaron GTs, New Yorker, and Lancer models, Pack says the figure could run quite a bit higher. In 1985 alone, GM sold 120,000 Delco/Bose units. Ford expected to equip 15 percent of its '86 Continentals with its JBL sound system, but wound up installing them in 30 percent.

``Our original estimates were quite conservative,'' notes Thomas Wagner, general manager of Ford's Lincoln/Mercury Division.

Unfortunately, the boom in high-quality car stereos does have a big drawback: The systems have become a prime target for thieves.

``I would say it's a terrible problem,'' comments Aaron Lowe, a spokesman for the Vehicle Security Association, ``particularly in areas like Los Angeles, where drivers spend a lot of time in their cars and tend to have expensive radios.''

Mr. Lowe says there are no specific figures detailing the increase in the theft of car audio systems, but he notes that overall car theft rose by 7 percent in 1985 and is expected to post a similar increase when the 1986 figures are tallied. According to some reports, the theft of radios and other property from parked cars is rising equally fast.

To deal with the problem, some manufacturers have begun selling removable radios and tape players, which can be pulled out of the dash and hidden under a seat or in the trunk when a driver is away.

Aftermarket suppliers such as Nakamichi and carmakers such as BMW have also started using antitheft programming, so that the radio will not play once removed from its dashboard mount.

To make it work again, the reactivation code has to be entered within a certain number of tries; otherwise, the unit simply goes dead. Despite these features, Lowe says he is not optimistic: ``As long as people get good car stereos, the theft problem is going to continue.''