Getting Jaguar to growl -- quietly
Wrench. Screwdriver. Stethoscope.
Car companies go to a lot of trouble to perfect the sound of their vehicles. Perhaps no other brand has as much emotion invested as Jaguar. For reasons that almost seem like animism, a big cat from Castle Bromwich has to purr, snarl and growl.
To better achieve a repertoire of feline sounds for the new XK coupe/convertible, which goes on sale early next year, Jaguar engineers created a semi-active exhaust system comprising a set of spring-loaded plunger valves located in the inlet pipes of the “silencer,” which is what we Yanks call the muffler. This helps give the car a mellow, refined exhaust note while the car is cruising, say Jaguar engineers.
But when the driver opens the throttle, the increased exhaust gas pressure pushes the valves open, changing the exhaust sound to a bright metallic snarl Jaguar engineers identify as a “sophisticated European sports car” sound quality.
The sound of a car is actually a combination of sounds, less a note than a chord, combining frequencies from the intake side -- the sound of the engine -- and the exhaust side.
To help balance these sources, Jaguar routed a small sound pathway from the front of the engine into the cabin, tuned in such a way as to enhance the engine note’s color and timbre.
None of this is revolutionary technology; what’s unusual is how specific Jag was about the color and timbre of the sound quality. As seen on a computer graphic, the Jaguar’s target sound is a blend of a “crispy” 700-800 hertz induction sounds, low-frequency exhaust growl around 200-400 Hz, and the nearly sub-aural, concussive sounds of the pumping V8. Mee-ow.
During a recent factory visit, I interviewed Brian Crossland, Jaguar’s principal engineer for sports car refinement.
In your title, what does “refinement” mean?
In layman’s terms it’s about getting rid of the noise, vibration and harshness in the car.
Aren’t sports cars supposed to have a certain lack of refinement? How do you define the sound of a sports car?
It’s about creating the balance, and that’s what we’ve tried to do with this car, to make sure we have this quiet, refined cruising mode and yet introduce in the enthusiastic sporting mode the intake and exhaust contribution for sound quality aspects.
What about aesthetics? What is distinctive about a Jaguar sound?
Inherently, there is the underlying, powerful growl with the characteristic V8 note. It’s also about generating an engine note that is crispy and pure.
What is “crispy”?
A clear definition of the sound: When you listen to it, it’s clear and defined and not wooly around the edges.
Why is sound important?
It evokes a lot of emotions, particularly in this class of car, and it’s distinctive -- it’s associated with the vehicle. It’s about going down to the golf club, or wherever, and starting the car up and showing it to your friends. And it immediately enhances the quality of the car and the perception of the people with that car.
Do you think people test drive cars, like them but walk away because they don’t like the sound?
Absolutely, sound can make or break a car.
