You probably already know, that the the most difficult parts for a big orchestra to master, are the soft, quietly played passages. To hold the tension, then, when only few sounds are to be played, requires particular attention. In our cars it's exactly the same thing. They are becoming continually quieter, which makes the search for annoying noises more and more tricky.
You probably already know that the quality of a car is often (wrongly) judged by the sound of the closing doors. Something new however, is that the noises are not simply ironed out during the constructing but that existing sounds are specially designed. At the latest now, it becomes clear that empirical measuring is not much use here. My new garden-pump is labeled at having a noise level of '65 dB'. The only problem is, I still find it pretty loud.
Thereby, what we think we're hearing is, by no means what our ear perceives. Indeed, between sound and perception, lies the brain, which is a filter. That's why a sound which has just been heared, is different when comparing it with the recording thereof. The most surprising difference is, when listening to a recording of ones own voice.
Thus, that which is heard, is individually perceived, the same as, e.g., what an accident witness believes to have seen. This makes it all the more difficult for the acousticians, to create a quieter or more pleasant sounding car for a large spectrum of potential buyers. Another aspect is, that the make-up of sounds is very complex.
A good example is the 1993 Mercedes C-class, whose Diesel-engines worked satisfyingly together with the E-class, however, here they created unpleasant noises, which was damaging to the image of the car. This means that the engine and the bodywork don't fit together well. The advantage is, that both components come come the same manufacturer, Mercedes Benz.
Nowadays, the factories make the products themselves more and more rarely and the suppliers, according to themselves, deliver about 80% of the car. Can you imagine how closely together they have to work, to avoid a disaster happening? Should the worst come to the worst, even more cooperation is necessary. This is one of the reasons why the manufacturers have taken the supplier directly onto their premises.
To get back to the garden again, if my neighbour would mow his lawn in one go, it would be less annoying than if he would stop occasionally and then start again. Naturally, perfect silence is a blessing that fewer and fewer people are in the position to achieve. I, e.g., find the noise that children make, quite pleasant.
As you can see, the same noise levels are very differently judged. The expansion-angle of sounds is also a very important factor. It took me quite a while to understand the previous configuration of the speakers in the top of the dashboard. It was in fact, all about the reflexion of sound from the sloping windscreen.
The simplest thing to do, would be to create a vacuum in the car's interior. Then however, we would have to drive with oxygen masks. From this example, we can see that sound waves are transferred through the air as oscillations. Deep tones are created through slowly following waves, high amplitudes are exactly the opposite, high tones are hardly noticeable on the membrane of the speakers.
Sounds are sent out from the center-point in all directions. In the most favourable case, into the carpeting, where they are irrevocably lost. Because our ears are seldom pointed directly in the direction of the emitted sound, what we perceive, is mostly reflected sound, which again, depends on the nature of the reflexion surfaces.
Take a drive in a camper before and after the refitting and you'll notice the difference straight away. Loud, by the way, means high amplitude, the frequency determines the pitch. In the worst case, it is not only reflected, but rather a sound source is added. Then it becomes more difficult because an overlapping of the sound waves occurs.
You surely know this already: In-phase waves strengthen each other, shifted-phase waves are weakened. The precondition for such pure theory is: The frequency must be relatively well matched, otherwise the the particularly loud and quiet tones will alternate. More refined are systems, which constantly measure the sound level and activate suitable counter-noise.
Something like this is already built into top of the range vehicles. Indeed, it is also not easy to manage. Should only the driver be protected, or all the passengers as well? Does everyone even want complete silence? Give a thought to the various racing exhaust fans. I mean really, a Ferrari without sound?, inconceivable!
You've more than likely read-, on our site, or heard about, speakers in the exhaust system. That means you can select the sound from the driver's seat. Today you may be in a bit of a bad mood, then you won't want to hear any noise from behind. On the other hand you may want to give it stick, and the whole world should be able to enjoy it. This is something that we haven't even spoken about, the difference between what we hear from inside the car or from the outside.
So, it shouldn't be too quiet, and there are also those who fancy the car as a rolling concert hall and others still, as an ego-extension. How can one do justice to all these various characters? Generally,the legislator expects that the warning sirens of ambulances or other assistance vehicles must be able to be heard, which is also the reason why head-phones are not allowed.
The direction seems, once again, to be an electronic regulation system, which applies explicit counter-sound exactly the milli-second it is required. Somewhere along the line the advocates of original motoring, who take long motorway trips. at best, in an old, standard Beetle, will again make themselves heard. Radio-listening, in this case, can only be enjoyed when the volume is really turned up.
Give a thought to the environment. How much did we spend in the past, to get a six-cylinder. Nowadays, downsizing is fashionable. We now imitate the six-cyl. sound through sound designing, no-one looks under the bonnet any more anyhow. Perhaps even Ferrari-sound on demand from a Diesel engine, and this, almost without extra cost, that would be quite something. 07/12