Cars make a lot of noise. Even electric cars, that seemingly whizz about silently, will have a distinct sound - and every sound your car makes has probably been analysed, checked and tweaked to perfection. Manufacturers will check everything from the sound of the engine to the noise a door makes when it shuts; luxury cars always have a distinctive, expensive-sounding thud on closing the door. This is not a coincidence.
So how are these sounds checked? That’s where odd-looking rooms like the ones you see in the pictures here come in. They have varying names, but pretty much all of them work off the principal of an anechoic chamber. An anechoic chamber is essentially a soundproof room which limits the reflection of soundwaves in order to provide the cleanest possible environment to hear noises.
To simplify this massively, here’s how it works: the walls of a room are covered in foam shapes (usually some form of triangle, however depending on the frequencies you wish to nullify, the shapes can change) which absorb the sound waves. Thanks to the material these shapes are made from, sound does not reflect readily, while the shapes are designed to reflect any noise that does escape towards each other, rather than back into the room. This allows the walls to absorb sound, meaning recording equipment will not pick up on any external noises that may interfere with what’s being measured.
You may have heard of car manufacturers talking about NVH. That’s noise, vibration, and harshness, to you and I. It’s an important aspect of building a car, as any shakes and rattles will lower the perceived value of a car hugely. Therefore, by using these chambers, manufacturers can more readily isolate any unwanted noises.
There are a wide variety of different chambers that allow different objects to be recorded, with semi-anechoic chambers often used in the car industry - these are so-called because a heavy car would damage a fully anechoic chamber’s floor, so a semi-anechoic room will have solid flooring. For recording an engine under load, there are chambers with rolling roads inside, which allow for a more controlled environment for listening to a car at speed. A row of microphones allows technicians to simulate what a car sounds like while driving past.
Another form of anechoic chamber is an electromagnetic compatibility chamber (EMC). These do not measure audio, rather the electromagnetic fields emitted by electronic devices. You may have seen cars within such chambers after having audio equipment fitted; Adnan recently visited the guys at Alpine to get a new CarPlay headunit installed, and its guys popped the car in an EMC chamber to check the unit.
The building of a car is, obviously, an incredibly complex and time-consuming process, and it’s always fascinating to learn more about what goes on behind the scenes. So next time you shut your car door, listen up and remember that a team of people stood around an anechoic chamber and decided that that noise was acceptable!