Lexus is about to launch the LC 500 Convertible, the company's first soft-top since the sort-lived IS coupe-cabrio of the mid-2000s. In doing so, the Japanese company wanted to create a cockpit that lived up to its reputation for refinement, but also allowed in the noises that you want...
Acoustic technologies
Chief amongst those is the burble of the big, naturally-aspirated V8 engine sitting up front. "A continuous, pulsating sound is characteristic of a large-capacity, naturally aspirated V8 engine like the five-litre unit which powers the LC 500 Convertible" said a Lexus spokesperson.
"Lexus has used acoustic technologies to combine this with spectral harmony, - perfect sound intervals that are pleasing to the ear - stereophonic sound, - to create a depth of sound - and formats - qualities that stir the senses and generate a feel-good factor."
Not only that, but Lexus is using the car's stereo system to 'clean up' the V8's noise profile, using an 'anti-pulse' generator that helps to quell any booming noises as the engine passes through its rev range.
Harmony of opposites
Lexus says that it's drawing on expertise gained from developing the LF-A supercar to help it create a cabin for the LC Convertible that's both quiet enough at a cruise, but which also lets you hear that mighty V8. The company calls that mixture a 'harmony of opposites'. Lexus says that in spite of the V8's exhaust note being as entertaining as you'd hope, the cabin is still quiet enough even when the roof is down for easy conversation.
In the LC Coupe, Lexus' active sound system uses a roof-mounted microphone to monitor the noises in the cabin. Obviously, that's not going to work in a convertible, and so the microphone has been moved to the drivers' seat headrest and the algorithm that controls the system has been recalibrated to allow for that.
Roof storage
Lexus has used acoustic simulations to find where the major sources of unwanted noise are coming from, and one major source turned out to be the storage area behind the seats where the convertible top is stowed. "It was a route for tyre and exhaust noise to enter the cabin. There was not enough room for soundproofing material to be added, so the team looked instead at adapting the trim material itself. By allowing air to pass through the structure and using sound-absorbing material on the reverse, the entire surface of the storage space soaks up noise" said Lexus. The surface used in the end is a modified version of the same material used for the wheel-arch liners.