Producing music with the immediacy of a live performance takes the meticulous efforts of an engineer and the appreciation of a music fan. So it helps that at Bose's Automotive Systems Division, the design-quality engineering department is comprised of engineers and technicians, who are also music aficionados and musicians. Using the company's components, the 33-member team tailors automotive sound systems to each vehicle model. Starting with the 1983 Cadillac Seville—which housed the auto industry's first custom-designed, factory-installed sound system—Bose engineers have specialized in heightening car drivers and passengers' listening experience by producing top-of-the-line sound quality.

To make sure that each new Bose audio amplifier and speaker performs under all possible vehicle conditions, the design-quality engineers conduct a comprehensive design-verification process before production. Components undergo electrical, climatic, and reliability tests, among others. What's more, based on their specialty, engineers use a number of test parameters on automotive amplifiers and speakers; for example, electrical engineers test for frequency response and output power, while mechanical engineers evaluate shock and vibration. At the end of the test process, only the most dependable amplifiers and speakers make it to production.

According to team manager and jazz fan Dave Leis, 95% of the design-validation tests are conducted in-house, while the rest is outsourced. First, the design-quality engineers, along with design engineers, examine a prototype to determine if it justifies a preproduction build. If they find that the product's new capabilities are worth the risk, they approve the assembly of a preproduction lot of up to 100 pieces. They then divide the 100-piece sample lot into groups for testing. Usually, 44 units are earmarked for design-validation testing, while 56 pieces are distributed to Bose design engineers, Bose audio-system engineers and the customer.

The typical 44-piece lot endures a lot of testing—with each suite of tests conducted in a separate lab, such as the reliability, dynamic, climatic, electrical and EMC (electromagnetic compatibility) lab. In the reliability test lab, for example, speakers are made to play high levels of a random-noise profile for many hours. In the dynamic lab, meanwhile, speakers and amplifiers are shaken and shock-tested at ambient and extreme temperatures. Moreover, in the climatic lab, speakers and amplifiers undergo several hundred hours of temperature, humidity and ultraviolet light tests, with some of the conditions they endure in the tests harsher than what they would experience in a vehicle. In the electrical lab, meanwhile, the equipment must show that it can work properly through many electrical conditions, such as voltage drops, polarity reversals, surges and shorts. Finally, in the EMC lab, amplifiers are tested for emissions and immunity. They must prove that they can handle a vehicle's severe electrical environment as well as not trigger the failure of other electronic vehicle subsystems.

Before and after going into each of these test labs, speakers and amplifiers have their parametric measurements taken. These numbers serve as the baseline from which engineers can evaluate a component's performance before and after a test. Finally, after all design-qualification tests have been performed, design-quality engineers look at the test results and confer with design engineers about any risks the tests expose. Engineers must decide whether they need to make changes to the product or if they can give the go-ahead for production. Even if they do give their approval, production doesn't start just yet. A product's production line must still undergo process validation. In the end, the result of this meticulous attention to detail is sound quality that's crisp, clear and consistently topnotch.

Source:

Music to Your Ears
Martin Rowe
Test & Measurement World, February 1, 2004
www.reed-electronics.com/tmworld/article/CA377226?pubdate=2%2F1%2F2004