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Unison is an extension of the concept of room correction, in which each speaker is equalized not only by means of a single filter at the speaker's input, but by using all other speakers in the system to help the main speaker attain an ideal target impulse and frequency response.

Dirac claims 'new approach' to sound optimization

Volvo is making Dirac's "active acoustic treatment of the listening space" technology (called Unison) available in the new XC90 with the Bowers & Wilkins audio system. According to Dirac, Unison co-optimizes the loudspeakers in frequency, time, and space for the "best possible bass integration and clarity," enabling re-creation of individual acoustic environments from certain performance venues such as Gothenurg Concert Hall located near Volvo headquarters.

In an e-mail response to Automotive Engineering, Dirac’s Lars-Johan Brännmark explained the technology:

"Unison is an extension of the concept of room correction, in which each speaker is equalized not only by means of a single filter at the speaker’s input, but by using all other speakers in the system to help the main speaker attain an ideal target impulse and frequency response. The loudspeaker to be equalized is called main speaker, and the rest of the speakers are called support speakers. The role of the support speakers is generally twofold: to extend the frequency range of the main speaker, in cases where the main speaker is band-limited; to actively counteract the acoustic response of the room caused by the main speaker.

"In a traditional single-channel approach to room correction, each speaker is viewed as a main speaker, and support speakers do not exist. A single-channel correction filter can adapt the time- and frequency response of the main speaker so that it interacts as smoothly as possible with the acoustics of a given room. However, neither the speaker’s frequency range nor the room acoustics can be significantly changed.

"Using Dirac Unison, the room acoustics can be altered in ways that are impossible to achieve with single-channel equalization. Speakers located at various positions in the room can act in-phase with the main speaker and out-of-phase with the room response, thus enhancing the main speaker and suppressing the influence of the room."

According to Volvo, the system uses combination of high-performance, low-distortion speaker designs, including extended-range aluminum tweeters and Kevlar midrange units, reflecting components found in Bowers & Wilkins premium loudspeakers. It also features a center speaker with Bowers & Wilkins tweeter-on-top technology for the first time in a car, providing a more open, spacious sound.

Specifically, the system consists of a 12-channel Harman 1400-W Class D amplifier serving a total of 19 Bowers & Wilkins speakers—seven Nautilus tweeters (25 mm) with the latest treble technology; seven midrange speakers (5 x 100 mm and 2 x 80 mm) with the characteristic yellow Bowers & Wilkins Kevlar cone clearly visible behind the cover; four cone woofers (200/165 mm); and the new, groundbreaking air-ventilated subwoofer (250 mm).

Dirac’s sound-processing software manages the timing of the sound and cooperation between the speakers to optimize the sound for a specific seating position, or all seating positions.

"Each loudspeaker in the system, subwoofers included, will produce the exact and proper amount of each source signal, in such a way that the desired time and frequency responses are reached at the listener's position," said Brännmark. "The desired responses are determined based on the locations of the main loudspeakers. Thus, a main speaker may itself be band-limited and lack the ability to reproduce low frequencies. However, if optimized with Dirac Unison, the main speaker will exhibit a well-timed full-frequency-band behavior thanks to the support provided by other speakers in the system."

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