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Lotus Engineering Develops Sound Simulation Technology for Electric Drive Vehicles

The Safe & Sound’ Hybrid system. Click to enlarge.

Lotus Engineering has developed technologies to synthesize external sound on electric and hybrid vehicles to counteract the growing concern these ‘quiet’ vehicles pose to pedestrians and cyclists. Lotus applied the technology to a standard Toyota Prius to create a ‘Safe & Sound’ Hybrid technology demonstrator vehicle.

The solution that Lotus has devised is a novel reapplication and development of its Sound Synthesis technology. Sound Synthesis is one element in the Lotus suite of patented active noise technologies, comprising three main systems each of which can be used individually or in combination: Active Road Noise Cancellation, Engine Order Cancellation and Sound Synthesis.

To synthesize the engine sound, a road speed signal is taken from the vehicle and a waterproof loudspeaker system is positioned adjacent to the radiator allowing the sound to emanate from the front of the vehicle. When the car is operating on the electric motor only, throttle and speed dependent synthesized sound projects a realistic engine sound in front of the vehicle. Once the vehicle has passed, the sound is not heard. 

The technology was designed around the behavior of a conventional engine, using an existing engine sound which makes it instantly recognisable with the pitch and frequency helping to identify vehicle distance and speed. If the hybrid’s engine starts operating, at higher speeds or throttle demands or lower battery levels, the control system automatically stops the external synthesis.

When the powertrain control system switches the car back to running on the electric motor only, the synthesis controller instantaneously sets the system running again. It is all completely automatic and the driver hears almost none of the additional sound.

In order to generate the engine sound, recordings of a suitable donor engine were made and analyzed to establish the characteristic frequencies at different engine speeds. These frequencies are then entered into the synthesis controller in the form of a ‘voice’ which outputs the sound through an amplifier and out through the loudspeakers.

Lotus Active Noise Technologies. Active Road Noise Cancellation (ARNC) and Engine Order Cancellation (EOC) look to reduce noise levels in the cabin, particularly at frequencies that are audibly unpleasant. In the case of road noise, the system reduces broadband noise levels at frequencies below 250Hz whereas EOC tackles harmonic frequencies generated by ignition events in the engine.

Input signals from the engine (for EOC) or sensors mounted to the suspension system (for ARNC) are fed into the electronic controller, as are sound signals, measured by microphones located in the cabin. The software algorithms of the controller then calculate what sound is needed to provide cancellation and the speakers of the in-car entertainment system are used to put this into the cabin. All this occurs in the space of a few hundredths of a second and repeats and adapts constantly through the control system, seamlessly and instantaneously adapting to changes in speed or road condition. The cancellation system operates on the input signals so other noise in the vehicle such as the audio system and speech are not interfered with or cancelled. The result is a quieter, more pleasant cabin.

The third system, Sound Synthesis,  enhances the sound in the cabin. The control system uses engine speed signal, a throttle position sensor and the in-car entertainment system to add sound. In this way a car could be made to sound sportier or be given the sound characters of, say, a flat 6 or V8 engine. Coupled with EOC and ARNC, the interior sound in the cabin can be tuned to enhance the driving experience and match the brand attributes of the vehicle.



I want my prius to sound like a sherman tank at full throttle.. on a bumpy road!


Good, now the garbage truck can wake me up at 6:00 am again. I was afraid the hybrid versions might be quiet.

Can't we come up with something like a dog whistle and provide the blind and cyclists with a receiver instead of making us all suffer with traffic noise?

As a sometimes cyclist, I appreciate being able to sense the car behind me, but as a human being, I don't want to listen to everyone's engine noise all the time -- like while sitting at the outdoor restaurant near a busy street.


Electric vehicles are far from silent, given tyre and other mechanical noises. The problem is the "background" noise levels are too high. As the overall noise pollution level drops, due to the changing ratio of electric to ICE vehicles, the perceived need for such a system will diminish.

The real solution is to remind cyclists that they should be using their eyes to detect traffic.

Gerald Shields, Seattle, WA

This makes sense . . . if you're (1) Blind (2) Deaf


The synthesis part of this is rather uninspired. Why not synthesize melodic sound, MIDI-type notation that at once identifies an approaching car (thru a recognizable range)and may individualize the vehicle - like ring tones do (huge aftermarket here.)

The concept of simulating old style V8 flat 8, etc. ICE engine noises keeps EVs tethered to combustion. Combustion is not the new way. With the help of some music and audio experts a bandwidth of acceptable "musical notation" could be established. Then, walking near a freeway filled with EVs the sound would be more symphonic, melodic - each different vehicle producing a unique melodic string.

With some forethought and planning the random combination of vehicle signatures will compose a pleasant audible experience whilst maintaining the requisite safety factors.

Of course for the monster truck clan - suitably dampened combustion sounds would not be denied.


Buses and garbage trucks are the bete-noir of urban living, particularly the loud and hot diesel buses with their hydrolic "kneeling" function and squealing brakes that drown out relatively pleasant noises from nearby jackhammers, screaming babies, and light artillery. I wish transit agencies would consider these things when they debate the economic and societal merits of hybrid and electric buses or garbage trucks. I doubt the fake engine noises designed for the Prius will bother anyone.


I When all the cars and trucks are electrified we will have the solution to traffic noise. Now it looks like Harley Davidson owners will be able to more easily justify their awful noise - "We need to make noise so other drivers can hear us coming!" Try sitting at a cafe when one of those drives up. I don't want noisy electric cars anymore than I want noisy motorcycles. People should always look before they cross the street anyway, even when on a rural road. Getting hit by a byicycle isn't fun either. Maybe we should require all bikers to put baseball cards in the spokes.


Yeah, and then you can download engine sounds just like ring tones. Just what we need, turning the streets in to the same circus.

If there is one thing I like about hybrids and (later) EV's it's that they are silent!

John Taylor

All that to come up with a shrill godawful noise?

They could have just given the car to a couple of boys from the ghetto and have huge woofers cranking out a blast of whatever "music?" that you didn't want to listen to anyways.

Silence is not really a problem in any car, not even an electric one.


This would be the most ridiculous unneccessary gadget on electrified vehicles. Kids, immature young and not so young immature mem would add 1000+ watts to simulate their beloved Holywood mufflers and Harley Davidsons's high level deafning sounds.

This would be a real potential desaster for most of us.

Chris L.

This article is a nightmare! Waterproof speakers blaring simulated engine noises? Maybe someone could develop a device that could spew out diesel fumes so we could smell an electric bus approaching.


Agreed! And how many little old ladies, deaf, disabled, blind, elderly, and children can one silent electric car kill??

We believe - the EV world should be administered for the exclusive use of the young, the strong and the very very green! Weak, poor, young and "unenlightened" - drop dead!


Well, I guess I didn't have time to wait for sound simulation technology; I hung 2 small bells under my Prius bumpers and it works swell.


fakebreaker, if you want to do comedy, i'm sure there's an open mic night where you can spew inanities to your hearts' content. I doubt there has been a single fatality in the world attributable to the lack of noise of an EV/hybrid; and how many people are killed by 'normal' ICE cars, with voluble engine noise and all? this is really a non-issue that has been trumped up by people who have a problem with greener cars on an ideological level for whatever reason.

David J

Has anyone done any studies on the noise various cars make under different scenarios? Like taking a Prius and a couple other compact cars, driving in a residential neighborhood by a sound meter at typical residential speeds. And also doing this in parking lots based on normal parking lot speeds and driving patterns.

I will go out on a limb here and say that the Prius in EV mode makes the same amount of noise as the comparable ICE compacts from the perspective of the sound meter.


the whole argument about electric cars being too quiet is stupid anyway. new ICE cars hardly make any noise at all except for the electric fans when they're stopped (which water cooled electric cars have too, or anything with a/c) and the tires and wind noise at speed which electric cars have as well.

Thomas Lankester

This idea is not 'for' cyclists, it is against them. One of the problems as a cyclist is people just stepping out in front of you because they don't hear you and do not think about cyclists. Now if the cars were quieter too then more people would look out and spot more cyclists.


Being an electrical engineer for thirty years, it has been natural for me to talk about how quiet the electric cars of the future will be, one moving part in the motor, no radiator, etc. So to add 300 Watt noise makers is a slap in the face. Maybe Lotus envisions a market for "car tones", fun stuff that will bring in money for them. On the other hand, my 94 Cougar V8 is very quiet when it's idling. Many times I've almost walked in front of ICE cars in parking lots because they are usually quiet when driving slowly. I looked left and stepped off the curb in London once and almost got killed. So maybe it is a trumped up issue to give some sly engineers an excuse to market a new product.


And does this wonderful system come complete with a fit and trim valet to wave a red flag or lantern, running ahead of the car as its proceeds through the streets?

Of course, I also hope it comes with full instructions to dismantle and hide the car in the bushes on the side of the road, were the automotive contraption to come across the path of livestock. Anything less would be a gross disregard of public safety.


300 watts LOL man what a waste of energy, that's 1/3 of the battery capacity of the prius!!!


What amazingly thoughtless comments -- especially from people who consider themselves to be Green.

I agree this may not be the best way, but hybrids and EVs will need to be made louder. Speaking from experience, a Prius is nearly impossible for a cyclist to hear as it approaches. Hybrids are already striking bicycles and pedestrians who didn't hear them coming. I hope one isn't somebody you care about.

Eric: the best comedy (aka satire) so discomforts its target - they complain, stomp their feet and cry "Heresy!"

The Empty Vessel

Here in the UK ice cream vans normally drive round playing some melodic tunes to attract customers, who knows maybe they do in the States too. Perhaps a similar system can be adapted for electric cars, although it might lead to hoards of children chasing EVs..... not good for road safety.


10 watts would be more than sufficient to achieve the same effect.


there should be an RF frequency reserved for 'close distance notification'. So in the future, anyone is free to program its cellfone, ipod, ... to play the sounds that are broadcast in the near distance.

If you like notifications of broadcasting cars, bikes, but also shops and other close-distance advertisement, you are free to switch on your device. If you prefer silence, you are free to enjoy it also

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