A story about cars, noises and vibrations

Did you hear this one coming?

Consider this:

You just grabbed your brand new high-end car’s key and you can already feel the excitement. The key feels heavy in your hand. It doesn’t creak when you press it. It doesn’t rattle when you play with it. So far so good.

You head over to your car, which, sensing the key approaching, starts the unlocking process. The wing mirrors unfold, emitting a noticeable yet expected whirring noise, while you can hear the doors unlocking; a neat, damped, single-event noise, not too loud yet loud enough so that you know it is now unlocked.

Next, you grab the door handle. It feels firm in your hand and you don’t feel any unwanted vibrations apart from the single impact when you pull on it. The door opens and you barely notice the unlatching noise nor the absence of squeak.

You can hear the steering wheel and seat moving in position but who has ever noticed these not to make noise when adjusting, right ? It’s not like it is inspiring anything else but refinement anyway; plus, cheaper cars might only have manual adjustment ones.

Your sound system plays a welcoming noise through the speakers, reminding you that you have a 30+ speaker 3000W sound system and you happily ignore the squeak your leather seat makes when you sit in it, cloth seats can’t do this.

You are now ready to start the engine. You press on the brake pedal, which doesn’t make a zipping or a deflating noise when fully pushed. You press the “start engine” button, which let you know you know that you performed this operation correctly by emitting a soft click and giving you the appropriate haptic feedback.

You can hear your engine starter cranking up, yet no shake can be felt in your seat, indicating a perfect control of the vibrations. This lasts for less than a second.

Your Vee engine then flares up to 6000rpm in a heartbeat, immediately giving you goosebumps and bringing a grin to your face. It then settles down at what sounds like fast idle, it might be louder - perhaps even boomier - than what you’d expect but at least you know it is prepping itself up and will be quieter soon; whatever.

You then engage the first gear by grabbing the automatic gearbox stick, you first notice the haptic feedback letting you know you engaged properly, then you hear the engine speed lowering and you feel the subtle vibrations in your hand. You let go of the brake pedal, start pressing the throttle pedal as you hear the electronic parking brake disengaging and you start to pull away.

In this introduction, this hypothetical car hasn’t even started moving and yet, can you count how many times I mentioned a noise or a vibration being perceived ?
How many of these do you think have been engineered, i.e. designed, assessed, measured and validated by a team of people, over countless iterations? Surely, many more than ever were a century ago, even for what we consider some of the most basic cars nowadays.

Would you expect most of these noises and vibrations ? Do you care about some - or most - of them? Why do you even think you would do so ?

This is what I will talk about, through the filter of NVH - Noise, Vibrations, Harshness: a story of brand building, engineering, expectations and perceptions; of what is acquired through objective measurements, subjective assessments and market research.

Powertrain noise, road noise, wind noise, breaking noise, buzzes, squeaks, rattles, HVAC noise and operational sound quality.

Modelling, regulations, historical trends, technological innovations, customer expectations, brand differentiation, benchmarking, development cycles, attributes balance.

Measurement techniques, psychoacoustics, facilities, metrics, problem solving methodologies, rules of thumbs, best practices,.

Sound systems, chimes, active noise cancellation.

In each post, we will explore one of these subjects by asking each time a simple question, such as:
What makes a 4-cylinder engine sound different to a 6-cylinder engine ? What about the intake system ? The exhaust system ? Why is the road noise better with a 19” tyre compared with a 21” tyre ? Does the wheel style even matter ? How is a squeaking noise generated ? How is it different from a rattling noise ? How much does it cost to fix or prevent any of these and how do we know if it is worth the investment ?

In each post, we will try and understand how some of these decisions are made, how they are measured and assessed. We will sometimes explore how troubleshooting is done, what are the compromises between NVH and safety or NVH and dynamic performance, what new challenges come with electric vehicles, new regulations, changing market conditions or changing customer expectations.

Stay tuned for the first post coming up soon and feel free to ask me whatever question you would like to see answered in a future post !

Want to know more about Powertrain Sound Quality ? Read the first article here:

PTSQ Series - 1: An ode to Engine Orders