Orchestrating Your Engine - Why Sound is Important

High end car brands place huge importance on the sound their vehicles make because of how they believe it affects potential buyers. Many have dedicated departments that spend millions on precisely tuning their cars to produce a very specific sound designed to induce the desired effect. 

Music to Our Ears

They use this sound to convey specific emotions and traits associated with that particular car, and their brand in general.  Some brands believe so much in this process they have created their own distinctive sound identities that are instantly recognisable for who they are – announcing the presence of one of their vehicles long before it’s seen.

The loss of this ability is a serious concern among some of them. They are worried about what their cars will sound like as we head into a possible Electric Vehicle revolution, and they potentially end up having to switch over as well.

Without the sound of a combustion engine will their cars still have the same appeal, the same emotional response and attachment? In truth, it’s a valid concern.

Lamborghini have long been against EV’s for this precise reason – they have insisted that the combustion engine is so intrinsic to what their performance cars are about, that they would lose that intangible quality that enraptures their customers if you were to take them away.

It is only just recently that they finally relaxed their stance and created the Terzio Millennio. A capitulation of sorts to the march of progress, but also a statement of a car designed to ensure their future by utilising the most cutting-edge of technologies - including electric motors.

BMW have even resorted to channelling artificially generated engine noise into the cabins of some of their models - to imitate a larger displacement in those cars with smaller and more efficient engines, and a combustion engine is those with electric or hybrid motors. But that’s cheating a bit isn’t it.

BIGGER IS BETTER, RIGHT?

Exactly how the noise a car makes is produced and then tuned of course starts inside the engine, and the type of noise created rests largely on three primary variables; the number of cylinders and their arrangement, the frequency with which those cylinders fire and the firing sequence of those cylinders.

The firing of a cylinder produces a pulse that emits through the exhaust valves, so having more cylinders in an engine increases the frequency of the pulses being created - and these pulses produce the beginnings of the engine note.

Car engines can range in size from as low as two cylinders like those found in most motorcycles, up to the 16 found in the Bugatti Veyron and Chiron - and even larger in some rarer instances.

Most production cars will have between four and six, with higher performance models having eight, ten or even 12 - although these larger sizes are becoming increasingly rare as designers find more power from smaller, lighter, faster engines.

FLAT OR CROSS?

Not screwdrivers, but types of crankshafts. The type of crankshaft the pistons are attached to has a drastic effect on the engine noise. There are two general types of crankshaft, cross-plane and flat-plane:

Cross-plane cranks have their piston rod journals arranged in four positions 90 degrees apart around the shaft, resembling a cross when viewed end on.

They cause less vibration than flat-plane cranks, but have a typically slower revolution speed.  This is because they are naturally heavier due to the counterweights that have to balance each journal position around the shaft – four positions means four sets of counter weights are needed.

Their slower firing rate means the gaps between firings are easily distinguishable at lower RPMs, providing a deeper rumble that builds to a roar under acceleration.

Flat-plane crankshafts are as described, flat, the have all their piston rod journals arranged opposite each other at 0 and 180 degrees when looked at end on.

Because the journal positions balance each other there is no need for the heavy counter weights used in a cross-plane crank, making the flat-plane lighter. This allows it to revolve at higher speeds and is quicker to accelerate - and is why it is used in higher RPM engines. These types of engines are typically a lot smaller with less displacement than cross-plane engines, but more than compensate for their lack of displacement with their faster rate of firing their cylinders.

The higher RPM means flat-plane crank driven engines produce a higher pitched whine when compared with the cross-planes growl, pushed up to a scream at higher speeds.

The downside is the increased vibration caused by these speeds. These vibrations can be extremely damaging if not balanced properly, and as this is difficult and expensive manufacturers only choose to use them in performance engines as they are ideally suited to racing.

ROUGH OR SMOOTH

The crankshaft determines the order in which each piston fires, specifically the layout of its journals where each piston rod is connected to it. The journals can be positioned so that the pistons could fire in almost any combination, but there are generally two ways an engines firing order can be categorised – alternating or non-alternating.  

Alternating firings switch between the two banks of cylinders continuously, creating a very even and smooth stream of pulse from the engine and down the exhaust. This in turn creates a consistent engine noise, with very little space heard between pulses if at all.

Non-alternating firings flip between firing one from each side to firing two on the same side and then back again. These periodic double-pulses down one side of the exhaust system create a drastically different sound – it is a much lower inconsistent rumble.

THE PERFECT RECIPE

If you were to then combine these three variables, you will likely end up with a piece of automotive history on your hands, as these are base ingredients for every legendary engine ever created before the trimmings are added.

The V8 is probably the most distinctive and beloved engine size and configuration, and part of its appeal is down to the two distinct engine types that use it.

There’s the iconic American V8, found in muscle cars like the Ford Mustang and Dodge Challenger. This engine combines the eight cylinders with a cross-plane crank to produce a slower, deeper rumble, with the uneven firing of its cylinders adding that unmistakable burbling sound. It’s one of the best sounding engines around.

 
The Challenger is at (6m55s) - but don’t dare skip the Plymouth Barracuda taking off at the beginning.

The other type is the European model, most famously used by Ferrari, pairing a fast spinning flat-plane crank with an alternating firing sequence to force a much higher pitch from the V8, making it sound more like a turbine than a motor.

This exhaust tuned Ferrari 458 gives you a perfect example of how much faster the flat-plane engine spins up to (0m25s)

FINE TUNING

Once you’ve got your engine sorted, the exhaust is where the amplification and fine tuning happens. Those lengths of tubing provide ample opportunity to create a unique sound through various size changes along the system, and narrowing and widening the bore to create specific engine notes is where famous brands hone their audio identities.

These specialist engineers tasked with the job spend many man hours careful tuning the exhaust system to achieve the perfect sound the brand is searching for, more akin to craftsman tuning their instruments than mechanics assembling automobiles.

We’ve already mentioned them, but you can’t talk about engine noise without talking about Ferrari. They’ve done more than anyone in cultivating their sound, and lot of their work goes beyond simply working the exhaust to produce the sound they want. An entire package of sound considered design decisions combine to produce their signature note, including short direct air intakes, a centrally positioned throttle, and tuned headers.

Their investment has rewarded them with perhaps the most recognisable engine sound in the world.

“A Ferrari doesn’t need a radio - its motor sounds like an orchestra”.
Herbert von Karajan - one of the greatest conductors of the 20^th century.

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