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The latest trends in Car Sound Car sound has come out of the dark ages during the last few years & a staggering range of new gear is now available to the enthusiast. It just depends on your budget. Pt.1 by JULIAN EDGAR Car sound systems have undergone a revolution in the last few years. The use of high quality compact discs has meant that amplifiers, speakers and other in-car components have become vastly more sophisticated to take full advantage of the digital sound source. Some manufacturers, such as Ford and Mazda, are now fitting subwoofers and powerful amplifiers in their topline cars. And in the aftermarket area, enthusiasts are squeezing in 15-inch sub-woofers, active crossovers and as many as three dual-channel amplifiers in their search for the ultimate sound. Competitions pitting enthusiast’s car sound systems against each other are 6  Silicon Chip being held around Australia. In short, the old manual pushbutton radio powering two dual-cone speakers screwed into the door trims has been left a long way behind. Front-end systems While the formerly ubiquitous AM/ FM radio-cassette unit has remained popular, CD players now dominate premium systems. CD changers which feature provision for six, 10 or even 12 CDs, are mounted in the boot, under a seat or in the glovebox, and allow the playing of up to 12 hours of music. A controller is normally integrated into the dash-mounted radio-cassette head-piece or the changer can use a separate remote control. The performance and ease of use of multi-CD systems has made it impossible for cassette players to compete. The Philips DC082 changer, for example, features a response of 5Hz - 20kHz ±1dB, total harmonic distortion (THD) of 0.03% at 1kHz, and a signal-to-noise ratio of 95dB. The Alpine 5952Z has even better specifications, with a THD of only .0008% (1kHz). CD players incorporated into a dash-mounted unit are also available, most capable of playing only one CD at a time. Howev­ er, Alpine’s dashmount­ed CD player will accept three CDs which are loaded into a magazine before being inserted into the unit. Of course cassette-based systems are still available. The Alpine 7620E, for example, has a claimed frequency response of 20Hz - 20kHz with metal tape, although no deviation figure is attached. Signal to noise ratio is up to 75dB with Dolby C and wow and flutter is just 0.06%. Most of these top-line units have an inbuilt amplifier, although the Alpine unit mentioned above is designed to be used with a separate amplifier and so has only line-level RCA outputs. Kenwood’s “cassette receiver” includes a 25W x 4-channel amplifi­er, while the Philips DC521 unit has a 12W x 4-channel amplifier. Signal processing It’s immediately following the signal source that some of the more recent innovations in car sound technology can be seen. Chief among the units positioned in the path between the signal source and the amplifier are equalisers and digital signal pro­ cessors (DSPs). Included in the range of sophisticated parametric equalis­ ers now available is the EQQ unit from Audio Control. This features full equalisation controls for both the front and rear speakers. All four channels can be individually equalised by seven bands of control and the unit also provides half-octave bass equalisation at 31.5Hz, 45Hz, 63Hz, 90Hz, 125Hz and 180Hz. Also included in the package are individual level adjustments for each stereo input and an 18dB/octave subsonic filter. DSP units can be used to provide surround sound, parametric graphic equalisation, listening position selection, and distinct­ ly different music environments. The equalisation system employed by the Pioneer unit, for example, allows one-third octave equali­sation and the unit can move the apparent focus of the music around the inside of the car by using audio delay techniques. The acoustics of five listening environments ranging from a studio to a stadium can also be re­ created and the effect is quite uncanny. Another interesting item is the Audio Control Epicenter, a device for those who like gut-wrenching bass. This unit searches for low frequency harmonic artifacts in the recording and then digitally restores the underlying fundamental which may have been lost through poor recording techniques. A control knob allows the effect to be tailored to your taste. A 36dB/octave subsonic filter is includ­ ed in the device. The unit produces extreme bass but it sounds quite different to the normal effects of bass boost, being much more natural. Amplifiers The boot was the only place in this car with sufficient room & ventilation for this Coustic 45W RMS x 4-channel amplifier. The amplifier is mounted on a hinged carpeted panel which can be swung out to give access to the car’s jack which is located in a recess behind it. This photo was taken during the installation process, with the wiring later tidied away. This end view of the Coustic amplifier clearly shows the RCA sockets for the left & right line-level inputs. A third set of RCS sockets provide a single mixed output with variable output level. Also located on this end panel are the variable high & low pass filter controls, the “peak” indicator LEDs, & the bass & treble boost switches. The “parallel” switch allows the input to the front channel to be internally fed to the back channel as well. CD changers, such as this Kenwood unit, can be mounted in the boot as shown here or under a seat inside the car. They provide good sound quality specifications, with some units ac­cepting up to 12 discs to provide 12 hours of music. Using (or having available) high January 1995  7 These Jaycar Super Tweeters can be mounted on the door sail panels (the triangular part of the door behind the wing mirrors). This location gives good stereo imaging. The rear deck of this demonstration car uses a new moulded fibre­glass parcel shelf. The mid-bass, midrange and treble drivers are located here. On one side, the speaker grilles are all in place while on the other side the grilles have been removed to show the individual loudspeakers. sound pressure levels (SPLs) is now the norm, with some systems capable of generating SPLs of over 125dB(A). Even those people who don’t want to suffer hearing damage specify high-power amplifiers to overcome road and wind noise and to achieve reasonable output levels from small, inefficient speakers. Multi-channel amplifiers are generally used, with some amplifiers featuring three stereo pairs. A 6-channel amplifier, for example, could be used in the following way: two channels driving front mid-bass speakers and tweeters, two channels driv­ing rear 2-way split or coaxial systems (typically 6 x 9-inch or 6-inch), and two channels driving twin subwoofers. A typical car amplifier of this sort is the Coustic AMP-660. It features a power output of 50W RMS x 6, with a maximum THD of 0.09%, a frequency response of 10Hz - 50kHz, and an A-weighted signal-to-noise ratio of better than 95dB. Maximum input current is a staggering 70A! For this system, you would be wise to significantly upgrade your car’s battery and alternator or use a separate battery and alternator to power the amplifier. The cost of quality amplifiers can be quite low, with a 4 x 45W amplifier boasting specifications similar to that quoted above retailing for around $500. A sophisticated equaliser has been fitted to the glovebox lid of this car. It might look impressive but glovebox utility is sub­stantially reduced! 8  Silicon Chip The trend in car amplifiers is towards multiple speakers in each channel being driven by a single high-current amplifier. Car speakers typically have an impedance of four ohms and so a series/parallel wiring arrangement can be used to allow a large number of speakers to be driven. In fact, many modern amplifiers are capable of working into speaker loads as low as two ohms. There are obviously problems in fading the levels from front to rear if the speakers on the left or right are driven from just one amplifier channel, though. Loudspeakers When it comes to loudspeakers, all top-line car audio systems use a mixture of tweeters, midrange drivers and woofers. The tweeters can be mounted on the A-pillars, within the dashboard, on the sails (the triangular areas on the doors where the mirrors mount), or even in the dashboard air vents. The directional nature of high audio frequencies means that tweeter positioning is critical in obtaining good staging effects. The front doors can obviously be used for speaker en­closures and this space is frequently used for midrange speak­ ers. This can involve fitting new inner door trims and these can be constructed of medium density fibreboard (MDF), or more re­cently be moulded from fibreglass. Once made, the new panel is covered in velour or cloth so that it matches the rest of the car’s interior. If the car is a traditional “threebox” sedan, the rear deck is generally used to mount 6 x 9-inch, 7 x 10-inch, 6-inch or 8-inch speakers. These can be coaxial types or two- or three-way designs, or can use separate drivers for the bass, midrange and treble. Of A standard dashboard speaker location (under the grille) can be used to house a midrange speaker or tweeter if you decide to upgrade to a high-quality system. The original loudspeaker that was used in this location is discarded. All is not what it seems here. While the top-of-the-line Kenwood KDC-9100 CD receiver is obvious, what isn’t so clear is the function of the cigarette lighter. It controls a hidden Epicenter bass accentuator. Pulling on the knob switches the device on, while rotating it controls the amount of bass. these, the three-way 6 x 9-inch loudspeakers are the most commonly used in this location. Cars that don’t have a suitable separate boot volume present greater problems when it comes to rear speaker placement. Common in hatchbacks is the replacement of the luggage cover with a strongly-braced MDF substitute, with the speakers mounted on that. Station wagons and other cars in which there is no other option sometimes use tube-mounted woofers, with the carpeted tube placed laterally or longitudinally within the cabin. SC This Earthquake 12-inch subwoofer is typical of some of the speakers now being squeezed into cars. It has a power handling capability of 300W RMS. This door has had a new fibreglass inner panel made to incorpo­rate new loudspeakers. They are located behind the grille cloth in the lower lefthand corner of the door. With the grille panel on, the door looks like this . . . . . . and with the grille panel removed, it looks like this. In this particular case, a 6-inch (150mm) mid-bass driver has been fitted, along with a separate tweeter to provide good quality sound. January 1995  9