October 5, 2005

Designing a Bose car audio system
By Jim Kerr

I love music. It could be the mesmerising rhythms of Santana, the gentle strains of Vivaldi, the soulful songs of Etta James or the driving bass of a little Black Sabbath. Different music for different moods, and like many of you, each album brings back many memories to me of past events, both good and bad. Cars and music have always had a strong association for me because many of my favourite selections were first heard while driving. That is why I appreciate a quality audio system in a vehicle. But a quality system doesn't happen by chance.

2006 Infiniti M. Click image to enlarge

Recently, I had the opportunity to enjoy some fine music with John Dion, Marketing Manager Automotive Systems Division of Bose Corporation while sitting in a new Infiniti M35 sedan. Bose is well known as a manufacturer of quality audio systems and speakers for both home and automobiles. Designing a quality system for automobiles presents several challenges and Dion was able to explain how Bose meets those challenges.

Designing a quality audio system starts many months before the vehicle is ever built. In the case of the Infiniti M, Bose sound engineers were involved from the start, almost three years before the first production vehicle. Infiniti made the design task easier by allowing Bose to place the 14 speakers used in the car in the best location for sound quality. Infiniti actually designed parts of the car around the sound system!

2006 Infiniti M. Click image to enlarge

According to Dion, one of the goals Bose has for any sound system is to reproduce music so it has the most natural sound, like it is a live performance. To accomplish this, Dion says more than 1000 acoustic measurements were analysed from inside the vehicle. Everything, from passenger seating positions to the materials used on seats were evaluated to optimize speaker position. Two tweeters were mounted in the A-pillars, a mid-range speaker in the centre dash, two "personal" speakers in each front seat beside the headrests, one speaker in each door, and two mid range and one subwoofer mounted on the rear window shelf.

Bose has developed their ideal curve for frequency response over the years and uses a custom computer program to balance both the speaker volume and frequency output. The Infiniti M uses a DVD 5.1 "Studio" Surround Sound system. The "Studio" moniker is part marketing, but represents the personal sound provided with the seat-mounted speakers one might hear in a studio. The 5.1 describes five channels of sound with frequency response from 3 Hz to 20 KHz and a sixth channel, typically through a subwoofer that reproduces frequencies from 3 Hz to 120 Hz.

2006 Infiniti M. Click image to enlarge

A car's interior environment is not static however. Windows may be rolled down causing wind noise. Rough roads may transmit noise to the interior. Exterior sounds are always a factor. Bose uses their AudioPilot noise compensation technology to counteract interfering noise. There is noise cancellation technology on the market that eliminates unwanted noises by producing a sound wave 180 degrees out of phase with the original sound. Honda uses this on their Odyssey to cancel engine noise under some operating conditions. Bose also makes headphones for pilots that cancel noises so voices can be heard clearer.

AudioPilot doesn't cancel noise however - it compensates by increasing speaker volumes in only the specific frequencies of the unwanted noise, so the music remains clear and clean. In the Infiniti M, a microphone mounted under the steering column captures the unwanted sounds so the system can compensate.

5.1 Surround Sound is popular in movie theatres and is becoming more popular in high-end home systems, but car systems are a little slow to catch up. The 2004 Acura TL had the first OEM automotive system. Even though the DVD audio sound is astoundingly better, part of the slow acceptance as I see it, is few people want to buy a DVD audio because it won't play in a regular CD player. The audio disc manufacturers have just started producing discs that have CD format on one side and DVD audio on the other side, so this stumbling block may soon be a thing of the past.

Finally, Infiniti understands that owners already have a selection of CD's, so the Bose sound system uses signal processing circuitry to separate sounds and frequencies into multiple channels to enhance the CD sound too.

There are other great sounding quality audio systems used in automobiles as original equipment, such as Mark Levinson, Harmon Kardon and Panasonic. Integrating the sound system design as part of the overall vehicle design has enabled Bose and Infiniti to offer one of the best automotive sound systems I have heard yet. It's like being front centre in the concert hall.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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