The importance of in-car audio systems as a model and image differentiator has increased markedly in recent years, and premium and top-of-the-market luxury car makers have been striving to provide very high quality systems.
Jaguar recently announced that buyers could specify Bowers & Wilkins systems in the new XF, and now Bentley has entered into a partnership with Naim Audio to incorporate in its models what it claims is the world’s most powerful in-car production amplifier, at 1100 W, combined with a “state-of-the-art” speaker system.
The main criterion laid down by Bentley for a new audio system was that it should provide sound equal to that of the world’s finest hi-fi within a car. It was a challenge, and Bentley and Naim spent 18 months jointly developing and refining the system for automotive use.
Tuned specifically for incorporation in each of Bentley’s models, it is linked with up to 15 speakers. Bentley is claiming another first for a car manufacturer by using a next-generation digital signal processor (DSP).
To achieve the required reproduction levels, Naim began by carrying out advanced acoustic analysis of individual cabins in Bentley’s sedan, coupe, and convertible range for the road conditions, including surface variations and aerodynamic effects, likely to be experienced by the cars.
“Resonance levels were measured throughout the cabin and bodywork to allow engineers to design unique speaker drive units for each car,” said Paul Stephenson, Managing Director of Naim Audio. The result is that, even with the system at full power, only a low level of sound can be detected outside the car—the complete opposite of what many young drivers strain to achieve, but very much part of Bentley’s message.
As always with automotive design—even a large Bentley—packaging efficiency was essential, and the amplifier had to fit into what Naim’s specialist designer Steve Sells called a “tiny area.”
“We needed to incorporate some of the most densely packed high-tech components imaginable and still ensure that the amplifier met our strict performance targets,” he explained. “The level of engineering that goes into the amplifier’s internals is unique. Every circuit board is optically checked by a computer-operated camera to ensure each component is perfectly oriented. It even checks the quality of each solder joint.”
He added that packaging constraints meant that a highly complex, double-sided, six-layer circuit board was necessary. Despite its very high output, a fanless design was created to avoid any interference from moving parts. The amplifier meets Bentley’s thermal management criteria of -40 to +70°C (-40 to +158°F).
The amplifier is assembled by hand to ensure that all circuit boards are lined up. Everything, including cable dressing and all inputs and outputs, is computer tested. The DSP provides eight modes. These include Naim’s “audiophile” mode (which it regards as the absolute reference setting for sound playback); driver optimized, balanced, and rear-optimized; digital media playback (via MP3 players and digital radio); spoken word; classic; and enhanced.
The DSP provides dynamic equalization, adjusts sound levels for every setting dependent on car speed, and avoids a possible time lag if a microphone is used to monitor background noise and then adjust levels. The Naim system has variable, dynamic equalizer sound settings, supplying a new level for every 1 km/h (0.6 mph) of speed change in the car. Every DSP setting has more than 300 equalizer levels, which vary for the convertible models depending on whether the roof is open or closed.The speakers use optimized magnet and voice coil systems, which, Bentley says, are rarely found in automotive audio systems. The speakers are driven by individual amplifier channels, which are controlled by the DSP.