Sound Improvements

The expectations of both drivers and passengers for electronic entertainment, communications and information have escalated since the introduction of the pioneering first practical auto radio, the Motorola branded AM car radio introduced in the 1930s by Galvin Manufacturing (who later changed their name to Motorola).

The latest cars, SUVs and trucks offer stock and premium entertainment packages beyond our wildest visions. DVD video with multiple fold fold-down LCD panel displays with fiber optic interconnection, navigation systems, Satellite/HD radio, mobile video and , THX surround sound.

Next generation electronic features and functionality will lend themselves to OEM equipped vehicles as designers struggle with size and weight reduction, long-term stability, environmental robustness, integration into larger assemblies and subsystems and the occasional request for cost down.

The Final Frontier

Interior space continues to get scarce and autosound aftermarket installers this year are confronted with a number of vehicles with none of the usual odd corners to install amplifiers, subwoofers and other electronic boxes. But while the OE interior engineers get to the scene first, the land grab is just as intense. While dashboard space is being eaten up by climate controls, air conditioning, air bags, navigation displays and so on, audio engineers are finding innovative technology in both audio electronics and speakers that provide significant space savings.

The Panasonic MXE CQ-C9800U CD receiver, 60W x 4 offers more real power in a space- and heat-saving package. By losing heat sinks, OEM’s can add better digital signal processors and bigger LCD monitors.

Until Panasonic introduced the first in-dash receiver utilizing highpower switching amplifiers this year (MXE CQ-C9800U CD receiver, 60Wx 4),, the commonmost head end units was were limited to fewer than 20 watts per channel (with Alpine’s V-Drive the former champion, at 26W x 4). Additional power and channels required amplifiers under the seat, built onto the speakers, or crammed into some other available space.

Higher power, in-dash head-end units have three significant implications for OEM designers. The Panasonic head unit offers more real power then many outboard amplifiers. A big impact is the space and heat savings. With the extra space created by getting rid of the heat sinks, OEMs can add better digital signal processors and bigger LCD monitors.

Switching amps allow for more channels in the head unit. Some OEMs are already looking at six channels for in-car-theater, but what about eight or 12 channels? With the horsepower in the DSP, active crossovers can be used to amplify each speaker driver separately while still fitting into a normal, single-DIN package.

The Panasonic uses the Tripath 60 W x 4-channel module, which features a built in DC-DC converter as well as Class T operation. “Class T” is Tripath’s name for their low distortion, full range sophisticated variation of Class D switching amplifier technology which is used by Panasonic and quite a few others, mostly in home theater and large screen TVs. Other vendors for switching amplifier ICs include Texas Instruments, and Apogee and ST.

Class AB amplifiers are by far the most common car amp design. Switching amplifiers (Class D) boast higher efficiency (some approaching 90 percent), produce less heat, and draw less current than traditional Class AB designs. Because they produce much less heat, Class D amplifiers can be housed in a much smaller chassis than a Class AB with the same power output.

For example, Tripath’s newest module is 4 x 100W and would be generating about 400W of heat if it were an AB amplifier. Adding the signal output power and the heat together, it’s pulling 800W from the battery. Changing to a switching amp, that same 800W from the battery can deliver 720W to the speakers, creating a 4 x 180W amplifier without pulling any more power, and only generating 80W of heat. Or in the case of the Tripath module, 400W of audio and about 40Wof heat.

As miniaturization and density increase, satellite radio, communication systems such as on-Star and equivalents, and the hands-free cellphones can be integrated into the head-end unit.

Signal Processing

With the newfound space in the head unit we now have more room for signal processing. The most basic signal processing is already in the head-end unit and can take the form of tone controls like bass and treble, and other functions to balance the sound from front to back or side to side. More sophisticated spatial signal processing is offered from SRS Labs like their Focus, which can bring the sound from your ankles (where the car door speakers are) to in front of you. THX, who originally developed standards for movie theaters and expanded to home theater, now has standards for autosound surround sound. Surround sound makes sense for cars as most vehicles already have speakers positioned in the front, sides and rear.

One of the most promising new signal processing techniques is MaxxBass. MaxxBass can provide a “virtual” subwoofer without the extra amp and subwoofer.

MaxxBass is an algorithm that utilizes the psychoacoustic “Phenomenon of the Missing Fundamental” to extended perceived bass frequency response by up to 1.5 octaves. In auto sound, MaxxBass enables door-mounted woofers that typically drop off below 80-100 Hz to sound like they can play down to 40-50Hz, giving consumers a subwoofer sound without the cost, size, power and weight previously required. This bass processing delivers more perceived bass while simultaneously reducing the likelihood of damaging speakers and amplifiers as woofer excursion requirements are reduced. Reduced displacement in woofers cone for a given apparent volume also translates to reduced woofer depth.

MaxxBass can be implemented with an ASIC supplied by Waves or it can be implemented in software in existing audio DSPs. Waves licensed the MaxxBass algorithm already to two Tier 1 OEM suppliers.

Speaker Developments

Where something more tangible than a “virtual” subwoofer is desired, a super-thin subwoofer is called for. Aurasound has an inverted magnet neodymium woofers, which is about 3ft.3-in. deep for an 8-in. diameter speaker, about half the depth of a conventional woofer. Another unusual bass product from Aurasound is their “bass shaker” which enables the bass to be felt in the seats. This is the same technology offered as an option in the Microsoft X-Box sound system.

The AuraSound NSF-8 is a shallow 8-in. subwoofer — only 2.4 in. thick. The slim profile is achieved by mounting the motor in front of the cone. The NSF8 uses a patented, inherently shielded NRT magnetic structure and an integrated heat sink to handle 150W RMS/600 peak W.

Neodymium magnets have dropped the weight by half of conventional ferrite car speakers and in the aftermarket have gained acceptance. As OEM designers fight for further weight savings, Neodymium woofers and tweeters will become the norm in OEM specs.

Flat panel speakers, after some delays, are showing up in OEM designs. NXT has licensed their technology for years, yet only this model year are viable flat panel NXT technology speakers reaching the showrooms. The speakers needed to overcome the challenges of surviving door slams and speed bumps, as well as meeting sound quality targets for more bass, efficiency and acoustic output levels. NXT’s latest implementation is the AFR (audio full range) which combines aspects of both conventional and NXT’s DML flexing diaphragm technology.

Paper speaker cones and the suspensions of the cone; the foam surrounds on the outer edge of the cone; and the spider attached underneath the cone, have always been the Achilles’ heal of the sound system. Wet strength of paper cones, the short life of polyester and polyether open cell foams for the surround, and the cottonimpregnated spider are an ongoing concern.

Car door speakers get splashed and rear deck speakers are exposed to UV. Specifications vary from vendor to vendor and characteristics vary over time. Now plastics from PPS non-cellulose pulps, newer stiff and lighter polypropylenes, and even aluminum are being introduced for cones while injection-molded Santoprene is being offered for the surround and spider. Overmolding the Santoprene — a TPV TPE thermoplastic rubber compound (used by automotive OEMs for gaskets and seals) — onto the cone enables unlimited operating life, high sensitivity, and stable operation.

Fiber optic control systems, used in a few premium vehicles for wiring harness weight reduction and installation simplicity, are now finding application in video distribution of the audio/video system from the head unit to the rear LCD display. Early field problems with terminations and the electronics interface have made the industry cautious in adopting fiber optics for OEM interface in video displays. While the trend is toward DVD mechanisms integrated into the fold-down display in the rear of the vehicle, interface with the front display (such as for the navigation system) may use Firewire or even a variant of Firewire over fiber optics.

Even the vehicle acoustics are benefiting from new materials technology to improve the listening environment. Monsanto has introduced a high noise immunity glass for car windows to keep road noise out, and was launched by Buick this model year. Materials Science introduced damped steel for the car industry for enhanced NVH. Two layers of steel are laminated with a thin plastic layer in-between. Rattles and buzzes are suppressed. Ford is aggressively featuring this technology in their new F150, as is Lexus.

Drivers and passengers expect new vehicles to offer more internal space with reduced external environment, with more features and functions, and a wider range of entertainment, communications and information, in lighter and better valued product offerings. These new materials and technologies are just the answer to those needs.