The Reason Behind Unique Engine Sounds - Engine Sounds Explained

Hello Guys, Everyone of us loves Cars and also it's sound. That "Vroom Vroom" Sound makes everyone drool for them. Each car has its very distinct sound, The stinging sound of a Boxer, Loud V8, A 12 cylinder Italian engines from the Lamborghini's. And good Old Japanese inline engines, Or a two stoke Humming of a Yamaha. What makes them sound different, Its not just the exhaust pipes and Mufflers. Come let's get to know more about those sweet sounds. 

Fundamentals of Sound:

To crack this out we need to know more about the basics of sound and its fundamentals.

The Reason we hear any sound is that the waves of different pressure travel through the air, Our ear capture this as a sound. Our eardrum is sensitive to these waves of different pressure. So it plays a very important role in hearing any sound.

Frequency And Pitch

The speed of the wave is called frequency, In other words How fast the Wave Ossilates is called Frequency, And it measured in Hertz (Hz). Ya, we learned in our 12th grade.

The frequency of the wave determines its Pitch. If the wave is slow (Low Frequency) it has a Low Pitch. If the wave is Fast (High Frequency) it has High pitch.

How Our Engine Makes Sound:

 Engine Sound is produced Right after a cylinder fires in our engine. And send the exhaust gases in form of pressurized air to the Exhaust Manifold. And these are called Pulses.

The rate of pulses Per second Gives us Frequency or pitch. The rate of the pulse is known as Frequency.

A sound is made up of various frequencies, Frequency with the largest Amplitude is called as Dominant Frequency or Root Tone. The pitch is directly linked with the RPM of the engine. That's why while we rev the engine it makes a different noise Than it sounder at idle. Ok, now let's get some Math in it.

Let's find our Engines Dominant Frequency Using our Engine RPM.

For that first we must convert RPM into RPS (Revolution Per Second),

 RPM   = RPS = HZ

   60

Now,

  60 RPM    = 1 RPS = 1 HZ

60 Seconds

In a 8 Cylinder V8, Idling @ 1000 RPM,

 If we apply the same Formula,

1000 RPM   = 16.66 RPS or 17 RPS = 17 HZ 

 60 Seconds                                            (For only One Cylinder)

We must consider the frequency of the cylinders that are firing in an engine.

 In a 4 stroke engine, Especially the V8 configuration, It fires 2 Cylinders once for every two turns of the crankshaft, ie two on each side of an engine block, Hence it is a V Configured Engine. This shows that only half the Amount of cylinders are firing. In inline 4 cylinder engine only two cylinders fires in one crankshaft rotation, but in V8 there is a cylinder firing at every 90° rotation which means half the amount of cylinder fires in one crankshaft rotation.

So let's make it simple, Whatever your Cylinder Count may be, Every cylinder fires once for every two rotations of the engine's crankshaft. It means half the cylinders must have fired in 1 rotation of the crankshaft. So in any Engine, only half the amount of cylinder will fire during one Rotation of the Crankshaft.

Now, In a V8, 

              4         x      17 Hz     =   68 Hz

       (Half Of 8     (Frequency      (Dominant

       Cylinders)     of 1 cylinder)   Frequency)

Now we know the formula for the dominant Frequency,

RPS of an Engine  X  No of cylinders Firing = Dominant Frequency (Hz)

(1 RPS= 1 Hz)

Example,
In a V10 Engine @ 5000 RPM

5000 RPM   =  83.33 RPS or 83 RPS (For One Cylinder)
 60 Seconds

No Of Cylinders Firing in a V10 = 5 Cylinders per crank rotation

5  X 83.33 = 415 Hz 

The Dominant Frequency Is 415 Hz.
Remember this is Just the Dominant Frequency Of an engine at a particular Engine Load or RPM, The sound Varies throughout our engine RPM and also we have other small quieter tones which makes the car sound more pleasant

Ya, we have done this boys, But there are some other important factors that decide the roar of your car. Such as the resonant frequency of the Engine Bay or the Thickness of the Sheet Metal used in the Car, Even the Metal used in the engine block, Diameter Of the Piping used in the Exhaust, Yes Exhaust System also plays a major role in our cars sound.

Exhaust System:

They are one of the big reasons that cars sound different, The Muffler/Silencer Diameter is important in an exhaust system the larger the Diameter the more exhaust gas it can let out.
They aid in dampening vehicle emissions and engine noise. They are made of steel and are coated with aluminum to provide protection from the heat and chemicals released from the exhaust system. Mufflers are used mainly to dissipate the loud sounds created by the engine’s pistons and valves. Every time your exhaust valve opens, a large burst of the burnt gases used during your engine’s combustion is released into the exhaust system. This release of gases creates very powerful sound waves. For example, a big Fart Can Exhaust Lets out more air in a single time and this creates a more Bassier Tone. Also, note that fitting a big exhaust in a tiny engine will not give any major improvement because they give out only a little amount of exhaust gas.

Intake System:

The Intake Also makes your car sound a way lot interesting than your Stock Intake. The Stock Intake is made To reduce the noise and vibration during the Intake. The intake upgrade is often considered as the easiest update you give to your car. Remember that an intake exhaust also makes more air to enter into the Intake Manifold and. If a slight tuning is done to the Ignition system. We can pump in more fuel and air, And every one of us knows that More Air + Fuel gives More Power. This also makes more engine sound.

Sound Based On Engine Type:

The sound of a car is also based on which engine it runs, A Rotary Engine is a completely different type of IC engine, A rotary engine has a unique combustion cycle. A rotary Engine Has 3 firings per rotation of the Accenture shaft, when the exhaust phase and the intake Phase overlap some of the exhaust gas moves into the intake chamber. This makes the Unique sound of the Rotary Engine which we can find In Mazda cars, The Legendary Rx7 are some of the sickest sounding cars ever, Also Mazda's Sky Active X Technology improved some flaws of the rotary engine.

The Boxer Engine also has a unique sound, They have Horizontally opposed engines and they are also called flat-four engines which we can find on Most of the Subaru's and Porsche's, Even VW beetle uses a Flat 4 Engine. Also, Boxers have a unique Firing Pattern.

But we can Notice that Porsche's Sound is More Pleasing and More sportier than Subaru, But I love Subaru's Boxer sound, The main difference is that the Subaru uses an unequal length of Headers in their exhaust. Which Means the exhaust gases from one side (pipe 1&3)has to travel a greater distance than the other side pistons (pipes 2&4). This male a lot of variation in sound. But Porsche's has equal length headers and, In the new Boxster with the 4 Cylinder, Flat 4 Turbo engine also has an unequal length of headers and has unique Mufflers and Resonators. You can learn more about the Boxer Engines Here.

Same Engine Type Also Differs in Sound and Why?

American V8 vs European V8:

Flat Plane Vs Cross Plane Crank

Yes, Even type of engine can differ in sound, An American V8 sounds entirely different from an European V8, Come lets Dig in Why, European V8 have an Flat Plane Crank which means the Crank Lobes on Crank Shaft are Separated By 180 degree. So each cylinder Fires in More Uniform Pattern and in a Balanced Manner. Each cylinder fires in a order opposite to the cylinder in the engine bay. American Engines have a Cross plane Crank which means the lobes are placed in 90 degree. Which makes the firing more inconsistent and two cylinders at the same side of the block firing at the same time, This makes a completely different sound than the European V8.

The NVH (Noise Vibration and Harshness) Department:

Yes, We love cars and its sweet Roar, But Auto manufacturers and Government dont want you to sound that loud, Hence every car Manufacturer and Government have their own NVH department to make the cars quiet. Eventually, Car Manufacturers Invest a lot of money for this Department, Some Countries have their own standards regarding the sound of a Car. In India, the  Sound limit for vehicles is around 80 Decibels. To know in detail about those sound levels click Here. 

Car Manufacturers spend lot of time and engineering, To make the cars less vibrating and sound quiet that's why most of the cars are now quiet. They experiment with different types of muffler design and Diameter, Bushings, Pipes and even the type of metal used in the exhaust pipings. Even engine mounts, sound insulators, Rubber bushes have experimented and they chose the best for their cars to be in accordance with the government standards.

Every one of us loves the sound of the car when we rev through the Redline, This is an Emotion For Us, And According to me Every Engine has a good sound. Hope this Post gave you some idea about the engine sound and Calculation of Engine Sound From Engine RPM, Go Take you Calculator Rev your Engine, and That's your engine sound.