How to cancel engine booming noise and enhance driving conditions

How to cancel engine booming noise and enhance driving conditions

Technology News |
By Christoph Hammerschmidt

Car designers have three contradictory forces to trade-off with:

In order to calibrate correctly an engine, every NVH (Noise, Vibration, and Harshness) engineer knows that there are three forces that have to be managed and balanced each one to the others:

Engine horsepower – Fuel consumption – Engine Noise

As for Engine power or horsepower, indeed it is a key feature as main focus of the car buyer. The first thing you’ll tell your friends when buying a sporty car or even a family pick-up. However due to new EcoTech downsizing constraint, the rules has changed: engines must keep the horsepowers but with less displacement.

EcoTech? Downsizing? This is how to get the best motor efficiency and get higher horsepower and increased torque on a new 1.6l compared to the last generation at 2.0l, even adding reduce fuel consumption.

Fuel efficiency is the second force to exert. It has become a major selling argument and car-makers seek to reduce vehicle weight in order to optimized not only fuel consumption and but also CO2 emissions.

European Union legislations require that any new car registered in the EU shall not emit more than an average of 130g CO2/km by 2015, meaning an average fuel consumption of 5.6 l/100 km (gasoline) or 4.9 l/100 km (diesel).

And by 2021, this limit moves to 95 g CO2/km, meaning an average fuel consumption of 4.1 l/100 km (gasoline) or 3.6 l/100 km (diesel).

Indeed, those CO2 emission regulations impose weight optimization of cars and using passive countermeasures such as sealing and sound- absorption material must be avoided, as generating more weight therefore more fuel consumption.

Therefore the noise shall be cancelled without the use of extra weighted material.

As an example on typical European car using a 4-cylinder engine, the most predominant noise is the 2nd order harmonic of the engine rotational speed.

When the engine speed ranges from 1200 to 6000 rpm, the 2nd order excitation traverses a frequency range of 40 Hz to 200 Hz.

Internal acoustic modes are excited in this frequency range resulting in an increased sound, known as:

Engine Booming Noise

Arkamys Active Noise Cancellation is a software solution aiming to reduce Engine Booming unwanted noise by creating another sound with the same amplitude but inverted phase to the original noise. The waves combine to a new wave and effectively cancel each other out.

Basically creating anti-noise to cancel noise means to have equal and opposite wave to cancel it. As the engine goes in higher frequencies, those wavelengths get shorter as a result having changes to the physical acoustics inside the cabin such as:

  • Windows up,
  • Windows down,
  • Location of where the passengers are,
  • At which height the heads of driver and passengers are located.

So higher frequency means it gets much more difficult by the time you get to the point where the frequency are there were short enough where just a little bit of tilting of the head or the seating position and heights of the occupants change – that’s when we start having problems.

So in practical sense trying to do cancellation above couple hundred hertz becomes quite difficult that is on a higher end.

And that also relates to ways to pinpoint certain areas to cancel, therefore using number of loudspeakers and number of microphones to catch the noise.

All those things become much more difficult as you go higher in frequency.

Having Arkamys Active Noise Cancellation gives three directs benefits to the driver and passengers:

  • reduction of booming noise,
  • long-term reduction of annoyance,
  • improvement of comfort.

It reduces Engine Booming Noise in car cabin and also improves in-car hands-free voice communication and in-car music listening experience, as music bass are also masked by low frequencies generated from engine noise.

It is using indoor microphones (2 to 4). The anti-noise signal is generated inside the car cabin through the loudspeakers of the vehicle. It can be implemented on a car head-unit on DSP or amplifier.

To cancel Engine booming noise, it has to work in frequency operation range from 40Hz to 200Hz which is the predominant engine harmonic.

Cancelling higher and lower frequency

If a car maker wants to cancel booming noise which is usually lower frequencies, it has to take into account that the frequency is lower as it goes lower in cylinder count. Therefore Car Makers need something that allows to reproduce low frequencies and place them in locations that are efficient to reproduce low frequencies.

Basically there is no use to put a small loudspeakers in the ceiling because that would not work. It needs to have loudspeakers that have decent size, position in front of the cabin like in doors or kick panel area and another one in rear of vehicle, as those are efficient locations to reproduce low frequency sound, not only for cancellation but also audio as well (such as Arkamys SoundStage, which is an software audio enhancement solution).

The sound field and propagation in the cabin is essential.

In order to reach that target, Arkamys provides algorithms that allow car makers to reach it in a way that it makes it very natural and seamless to people (driver, front and rear passengers) and that they do not know that Arkamys Active Noise Cancellation is installed and always on.

How engine does create booming noise?

Engines have fundamental 2nd, 3rd or 4th order and so on. Those orders are proportional to the RPM of the engine and that is how we measure things.

For example, if a car engine has 4 cylinders, engine dominant booming noise comes from 2nd order which means that the frequency is proportional to the second, 2x the rotational speed of the engine.

So if the engine is idling at 1,200 RPM, it means 1,200 revolutions per minute. There are 60 seconds to a minute. Then 1,200 RPM is 20 Hz.

That means that 1,200 RPM is the fundamental, engines spinning at 20 Hz.

Then 2nd order means 40 Hz, the 3rd order means 60 Hz.

To sharply measure it, car makers take into account RPM and they track noises by each order.

So it is a lot easier for car companies to measure cancellation to reach, because dominant motors are very well defined, so if it is a 4-cylinder engine, they measure the 2nd order and see how the system sounds with Active Noise Cancellation ON and OFF.

Audio-system pre-requisites

However, not every vehicle can support this kind of software solution. There are many architecture and hardware pre-requirements to ensure the best noise cancelling:

First of all there must be an amplifier or radio with DSP and sufficient processing power (MIPS, memory) coupled with a quality audio system with linear behaviour of amplifier and loudspeakers. To capture the noise, up to 4 microphones are needed, and better to be located in the headliner.

The car must be equipped with up to 5 independent loudspeaker channels, with front & rear speakers capable of playing 40 to 200Hz.

A subwoofer is usually strongly recommended. Not mandatory but recommended.

(fig. 2: ANC setup)

Indeed, the lower you go in frequency, the better of Active Noise Cancellation you get. And below 40Hz, the speakers may work less. However in case of very high value audio system in the car including subwoofer, then the Active Noise Cancellation can go up to 23Hz at minimum.

In any case, the best configuration is when microphones and speakers frequencies (bandwidth) are equivalent.

Finally, an insufficient power amplifier could lead to reduced low frequency performances. It has to be bear in mind when designing the acoustic and audio system inside a vehicle. In order to maintain real-time analysis and noise treatment, a real-time engine speed signal or high-speed CAN must be available too.

Optimize the audio configuration

In order to be full optimized, the system must respect a certain quality speaker’s configuration.Active Noise Cancellation controller shall have at least 4 channels of cancellation output to meet front seat performance and at least 6 channels of cancellation output to meet front and rear seat cancellation performance.

OEM shall decide the level of cancellation and cost factor that goes into the number of microphones or loud-speakers. Having 3 microphones versus 2 microphones solution gives a wider frequency band of cancellation but increase vehicle BOM.

Premium vehicles require larger zones of cancellation and highest frequency of cancellation. The pre-requirement is 4 microphones and 5 to 6 channels of loud-speakers in order to provide very good cancellation for front and rear while cancelling highest frequency possible.

Standard vehicle are likely to require more modest cancellation with 2 microphones only.

On Premium vehicle, to optimize the placement of microphones and loud-speakers, it is better to bear in mind a great number of freedom degrees meaning that number of channels (input channels and output channels).

It is basic fact: the more channels there are, the more it’s easier to create larger zone of silence.

In the lower frequency where 4 door speakers are adequate – lot of applications and car audio and infotainment mainstream these days – Arkamys believes that door speakers might be adequate, if car companies stay not much higher than a hundred hertz or so.


Arkamys Active Noise Cancellation package and performances


Arkamys ANC solution reduces Booming Noise for 3 to 8-cylinders engines. The measured consumptions based on SHARC AD21489 are 82 MIPS and 310kB Memory (split as 288kB for binary and 22kB for parameters). It can work on one or two engine orders at the same time. However, doubling engine order means irremediably doubling processor load.

Arkamys Active Noise Cancellation reaches up between 8 to 12 dB attenuation of predominant engine harmonic. Every car is specific, and the active noise cancellation is not predictive, as the sound field and propagation in the cabin is essential, as well as performances of speakers and microphones.

It works in frequency operation range from 40Hz to 200Hz which is the predominant engine harmonic. However, it can also support operation range from 23Hz to 40Hz under certain conditions.



As every Arkamys software solution, the delivery package to Car Makers is split into three parts: Software, Tool and Service.

The delivered software and licensed function are delivered as a pre-compiled software library (ie: SHARC, Dirana3 with Hifi2core …) along with the supporting configuration data files. Today, this solution is available on major automotive chipsets.

The delivered tool known as SAT standing for Silence Adjustment Tool is a professional PC-based tuning tool allowing to control active noise cancellation settings. It is a real-time driving tuning tool with direct connection to the head-unit.

Inside Service, we include sound tuning and/or training upon request. Arkamys can either perform all vehicles Active Noise Cancellation tuning or delivers tools to do so. Then specific training can be offered, as well as on-site engineering support for vehicle integration and tuning.

Some exception where ANC will not work correctly

It depends first on the microphone location: a sub-optimal microphone location too far from passengers head will lead to non-optimal cancellation at passenger head position.

Also if the speakers are unable to render powerful enough low frequencies, compared to engine frequency harmonics to cancel, will lead to non-optimal performances.

However, in any case, Active Noise Cancellation is inoperative when doors, windows or targa-top are opened or when car is set in convertible configuration.

Finally, when divergence are detected such as hardware default, changes in vehicle transfer function, or transducers characteristic variation with time or temperature, there is no possibility for the system to be fully operational.

At the end of the day, the benefits of having an Active Noise Cancellation solution are for the car-maker and for the end-user.

For car manufacturers, it implies no hardware change in the head-unit, speakers and audio configuration, except for the set of microphones and cabling that has to be installed and which has a cost. But in the meantime, it allows the reduction of use of damping and absorption material, which impacts the car structure weight. And in any case, variable displacement engine noises could not have been reduced by passive material. Having a real-time solution makes it possible.

And again, when it is time to talk about car weight reduction, it means also lower energy consumption and CO2 emission reduction.

As for end-users, clearly the first benefit is the less tiredness of driver and passengers due to engine noise. In the meantime it can improve the hands-free voice communication and enhance in-car music listening experience by reducing the perceived noise from the engine.

And the best benefit for the end-user, for the people who bought the car is also to increase in-car audio perception and therefore the value for money.

Test and measures: to ensure Active Noise Cancellation best performances

How car makers measure the ANC performances is pretty common: they put microphone systems on seating positions and they make measurements. There are laboratories that are equipped to make measurements in noise vibration harshness.

Every car company has slightly different ways of doing but they all pretty much put microphones in seating positions and figure out the performance so those are quantitative performances.

As for performance requirements, it is as always a matter of trade-off between cost and level of performance. It’s really up to car makers to decide how much they want to cancel.


But the main part of the job for Arkamys is also to make the link between NVH Engineer and Infotainment team, to help them understand each other’s needs and wants. It allows each group to understand what the trade-offs are and then they can make logical decisions for the Cost versus Benefit equation.

NVH and Infotainment Team traditionally never worked with one another. It’s like in a publishing world journalists talking to the guys in the printing press, they’re in the same company but usually not talking to each other. Some car makers have real big problems, some do a pretty good job of making peace but as usual each car maker is very different and that depends on each company’s behaviour and history.

If you want to cancel more noise you need more channels. But that also means higher cost so NVH Team need to figure out how they can get that money back by eliminating certain traditional countermeasures (mechanical parts, simplify the exhaust systems, reduce mass dampers and foams).

If a car maker is willing to remove a balance shaft from an engine, everyone know that’s a huge workload, there is the cost of the balance shaft but also to reduce parasitic loss and pumping loss of engines then they might say that the NVH team wants to put a 10-channel cancellation system. These are the economic values that car companies need to think about before they decide what is the target performance of noise reduction but at the same time Audio Team might say that there is no way even if NVH wants to put 10 channels in to justify the cost and effort of putting 10 channels of speakers everywhere for base level audio for some C segment vehicles.

Finally, the aim of Arkamys and its Active Noise Cancellation is also to be a peace broker between IVI In-Vehicle Infotainment and NVH Noise Vibration Harshness teams.

Is Active Noise Cancellation only for Premium segment vehicle?

High Technology is applied in higher priced vehicles but every car has its own set of NVH challenges and fuel efficiency challenges. This is where there is a market trend to go towards lower priced vehicles.

The wide adoption of this technology will come. But there is cost of technology, for algorithms and hardware (loud-speakers, microphones).

The key is how tough the problem is to solve. As we stated, if Car Maker wants to cancel higher frequencies, then it has to put in a larger number of microphones, like 3 to 4 microphones for example.

But with lower-cost vehicles, if the system requires to put more microphones, how to calculate the economic value that Car Maker put into the technology? Can it get money back by putting 3 microphones versus 2? Having wider frequency band of cancellation does it make economic sense?

Therefore it is not directly correlated to the vehicle price, although higher priced vehicles can absorb that cost much easier.

Some Premium vehicles that require larger zone of cancellation and highest frequency of cancellation incorporates 4-microphone system. That sort of configuration allows to have very good cancellation for front and rear and also maximizes the cancellation of the highest frequency as possible.

On the other end, there are cars with much more modest cancellation requirements in terms of higher frequency so it becomes possible to propose only a 2-microphones configuration.


Car Makers/OEMs want to make vehicles more silent when improving fuel consumption by tuning the engine which increases noise. Arkamys is developing software, tuning tools and support the integration, with always focus on overall cost reduction for Car Maker.

The great benefit of Arkamys technology is the integration. What we do is to integrate our software into existing hardware. We re-use the audio system, we re-use the amplifier. We do not deliver hardware components such as microphones or speakers as there are already companies well established in this market who know much better how to deal with those components. But we collaborate to find the best microphones and speakers positioning to ensure the optimized active noise cancellation.

But Arkamys Active Noise Cancellation defines also the sound rendering and the emotion of the powertrain of the car engine.

We don’t mess with that, because after all, that’s why we are buying cars!

About the author:

Mikael Breton is Product Marketing Manager, Arkamys.


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