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Thursday, September 16, 2021

No more fighting over the car radio as experts find a way to hear two songs without clashing

There are many sources of debate on a long road trip, including route selection, the choice of snacks, when to stop and, probably most importantly, what to play on the radio.

And while the driver may have a penchant for classical music, the children in the back and the passenger may loathe the likes of Bach and Mozart.

Finding a way for all parties to listen to their own audio without the need for headphones has been a goal of car manufacturers for decades, and scientists may have finally managed it.

A team from the University of Le Mans in France carefully positioned microphones, speakers and filters to create personalised sound zones (PSZs) inside a car, and these pockets of space are where sound from a set of speakers is audible. Outside this small region, it can not be heard.

One hurdle which scientists have previously been unable to overcome was the impact of moving one’s seat. They were able to form a PSZ, but unable to move it to follow a person if they moved the seat forwards or backwards.

Creating ‘bright’ and ‘dark’ zones

The French team created a new algorithm specifically to tackle this tissue, which manipulates the sound waves to create “bright” and “dark” zones throughout a cabin.

“This technology should eventually allow each passenger to listen to his or her own audio programme without disturbing others and without using headphones,” said Dr Lucas Vindrola, the author of the study.

“Loudspeakers are placed in the headrests, and specific filters for each transducer are calculated to reproduce an audio signal that retains good quality in the zone under consideration and is strongly attenuated in other zones.”

Multitude of microphones

The researchers found that if a bright zone was created around the head of the driver, the person sitting in the passenger seat would hear it 30 decibels quieter. This is roughly equivalent to the difference between having a normal conversation at home and whispering.

Dr Vindrola said that the key to the technique working properly was having enough microphones placed around the car to detect how many people are in the car and where they are sitting.

He said: “The price to pay is to have control microphones in the passenger compartment, so that the algorithm can work. The results remained interesting even when the number of control microphones was reduced.”

Not coming to a car near you

However, the technique is not yet ready to be commercially rolled out as a luxurious optional extra just yet, as it currently works only for a limited range of frequencies.

Sounds between 100Hz and 1,000Hz, a range that corresponds from bass notes to intelligible human speech, work in the prototype technique, but nothing lower or higher in pitch.

The researchers say the priority of their future work will be to look at expanding the range up to 10,000Hz, which would include all sound up to the highest note on a piano.

The full findings are published in The Journal of the Acoustical Society of America.

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