Active Noise Cancellation for cars not equipped

I am playing with an idea.
Higher end cars come with active noise cancellation systems to make the drive quieter and more enjoyable. However compact and subcompact class cars do not.
With the noise canceling technology is available on every shelf for headphones, I am wondering if this could be hacked and repurposed to reduce road noise in a car.
The system (Im presuming) would require one microphone, one noise canceling circuit board, and one speaker per wheel well.
So it would require two pair of noise canceling headphones to accomplish.

The idea is to improve the cabin noise quality in an off the shelf kind of way.
Currently there are no aftermarket systems within the normal financial reach of most people. Only a hand full of aftermarket systems out there are available and priced @ 4K USD or more.
If this works, it could be marketed at around 100 USD per unit. And provide a much nicer driving experience to the compact and subcompact cars. 
By placing the microphones under the carpet and on the wheel wells metal surface the system should ignore the stereo, and correct road noise transmitted from the wheels to reduce cabin noise. Stereo interference is a common problem with cabin mounted microphones on OEM systems.
So, your mission if you choose to accept it, is to devise a way to reduce road noise in a compact or subcompact car using off the shelf noise cancellation circuitry available to the average person.
If your successful this should be a very easy way to upgrade most cars not equipped with such a system. Having a noise canceling system in a car reduces noise fatigue, and improves the driving experience for all of us.

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RudolfŠ158 months ago

Question:

1. Cancellation of my voice when having phone call or live conversation in my office, because I dont want the talks to go through thin plasterboard wall between the two offices.

Idea: Having a mic near my head, connected to some electronics and amplifier driving some small midrange speakers (for speech OK) directed to the dividing wall (distance my head/speakers less than 5 metres).

2. Cancellation of street traffic noise going inside thru low cost plastics windows. Mic outside, speaker(s) placed inside on window sill, directed to my head.

Question: Will it work? Some experiences? Recommendations of cheap systems (ebay, China, etc.)?

Thank you for your replies. Please, send directly to snajdr.rudolf@email.cz

Thanx a lot!!!

Full diagram and research from Texas Instruments - http://www.ti.com/solution/active_noise_cancellati...

http://www.cvel.clemson.edu/auto/systems/active_ca...

I believe the price will come in closer to $250 for an off the shelf install yourself unit. We can start a go fund me page.

At $250 electronic solution may not even be the way to go. You could install "dynamat" in doors, floors etc. with bonus of better insulation and silencing door rattle from speakers.

I tried the TI link and couldn't get to the page. Do you have another link? Thanks.

Downunder35m11 months ago

Nice timimg for the resurrection LOL
I tried with a friend to silence an old Patrol, mainly the noise from the mud tyres and gearbox for long highway use towing a boat.
Our test equippment:
1. Pioneer car stereo with "active sound system" - it allows for a lot of DSP programs and sound ajustments for the positioning of the sound.
Meaning you can for example select "single driver" and really hear the sound as the speakers would be perfectly positioned for this.
2. Two sets of noise cancelling headphones - one for salvage, the other to compare the results to headphones on the head.
3. Time, beer and a lot of wires....
First obvious choice was to simply wire the electronics between stereo and amplifier.
Our problem here was the differences in the input/output levels, so some resistor bridge networks were made to compensate and the levels even.
The microphone was put on a long, shielded headphone wire to allow to different placements.
Result was just terrible with a lot of these nice feedback whistles.
Some beer later we realised the flaw in our approach: Headphones use external microphones to adjust the internal speaker sound with the mix to eliminate external noise.
What we tried was to eliminated all sound reaching the microphone, including the wanted ones LOL
So how to keep the speaker noise out of the microphone?
Next round required some modifications to the setup....
We again tried but this time using an audio input on the radio to "splice" the headphone electronics in.
This way the levels could be adjusted directly on the stereo and the sound would be mixed in before even reaching the amp.
Did I mention that it does not help to this on the go without thinking it over before starting?? LOL
Needless to say the electronics did not really care how the sound goes in or out, if the microphone hears music it still tries to cancel it out and messes with the results.
We went inside to replace the badly leaking cans with full ones and started some drawings (mind you noone could make heads or tails out of them the next day lol).
While being supplied with some fresh steaks from the BBQ it hit us hard!
The sound must stay with the microphone before going out into the amplifier system!
Two new microphones, a tiny stereo, line level amp and even more beer later we had the spare set of headphones destroyed enough to fit into a soundproof box with the mics next to the speakers and tiny amp inside.
While messing around I noticed a resistor on the headphones electronics in a place designed for a little potentiometer.
A test showed that messing here adjusts the signal mix so the range of normal voice frequencies still passes the filter.
Needless to mention that a potentiometer was added and set so the music was (almost) untouched while basically all external sound was cancelled out - much nicer than the original for plane use if you ask me...
The test with just the engine running was not too bad although the music did not sound right, was like certain frequencies got lost on the way.
So we designated a sober driver and went on the freeway to check the tire noise only to find out that the music got worse the louder the noise was.
Also the position of the microphone totally changed what happened to noise cancellation - up to the point of being really annoying.


Conclusion from my side:
It does not matter how you try to fool a noise cancelling hedphone set - it won't work in a car unless you use them on the head as intended.
Explanantion for the tech nerds:
By design these headphones mix an external signal, which is 180° out of phase, into the stereo mix going to these tiny speakers.
Additionally they are also quite good to keep external noise out by design, almost like ear muffs for work use.
It becomes quite obvious that no matter how you try at least one additional mixing and filtering stage is required to make it work in a car.
IMHO it should work like this:
At least two microphone inputs are mixed for the cancellation input.
All recorded sound, including what comes out of the stereo enters the first mixer stage.
Here all input signals are adjusted to the same level.
In the first filter stage the noise cancellation is applied based on the mixed sound form the first stage.
We now have a very distorted signal that would be terrible to listen to if you like music LOL
The setup should now be adjusted so that the sound is basically totally gone.
Don't worry if you can't do it properly as it is next to impossible due to the limitations of the car not being a perfect soundproof room.
Once the signals are filtered as good as possible it is time to fix the next stages.
The signal is now as good as we can go, which means we need to get our music back!
The next filter uses the previous input to eliminate all remains of the acutal audio signal we want to hear - this part I have not figured out fully yet as the music signal would need a DSP processor to remove the counterpart from the mixed signal, otherwise we just create unwanted noise again.
But we ignore that problem in favour of the theoretical stuff for now as otherwise I would now need to find ways to sycronise the signal timing as well ;)
In any case we now assume to have or active cancellation signal that is free of the music part.
The last mixer now overlays the real music signal onto the mixed and filtered cancellation signal.
This gives us a clean audio signal plus the sounds required to keep the noise down.

Obviously the more you like music the more problems you face, same if your car simply is very noisy due to age, tyres, exhaust and so on...
A stereo signal is hard enough to keep clean with and added cancellation sound, doing the same in a 5 or 7 channel DSP system is not possible IMHO - at least not on a hobby level.
And unless you already have a luxury car don't bother starting LOL
Keep in mind that in an expensive, quality car you won't really hear much coming from the outside to start with.
Where you in your daily driver will hear the cars next to you, the wind and all loose parts rattling around a big Merc or Audi will already be almost silent even without active noise cancellation.
You can hear the wind noise from the window with one ear more than with the other as a really simple example.
There is no way to cancel that noise out so the result is fully even at every seat in the car...

alfadog671 year ago

This is a concept that I have been pondering. I have a Chevy Equinox, which has in-car ANC, but it works only for engine sounds. I have Asperger's, and noise drives me absolutely bananas. My least favorite is crinkling plastic. But please excuse my digression.

It didn't occur to me to attack the sound at its source, ie. in the wheel wells, but rather at the destination. My idea is to place speaker/microphone pairs inside the cab, perhaps on either side of each headrest. This would lower all noises, such as road-to-wheel, wind, rain, engine and other automobile noise. However, it may dampen important sounds, such as sirens, horns, squealing tires and the all-important radio. It seems to me that there should be a button that, when hit, will listen to all of the ambient noise and block it only. That way, we can still hear the radio, the sirens, and in-cab conversation. It would probably be a digital filter of sorts, that memorizes not specific frequencies, but sound patterns, and reverses those patterns when the microphone sees them. I am almost an EE, and a programmer for decades, so there are some contributions I can make of anybody wants to collaborate.

ydeardorff (author)  alfadog671 year ago
It really should be too hard of a design. A muli-channel design would be difficult to setup, but 4 single units with a single speaker each should work (in theory).
Id start with the a junk pair of noise cancelling head phones, or other noise cancelling device. Then pull out the circuit for the noise cancelling. Hot glue the mic to the offending noise maker and then the output into a amplified speaker.
It may take some tweaking, but as each noise source is lowered, the overall sounds in the car will lowered. Again, in theory this is a possible way for it to work. Using other components and reworking / re-purposing them doesn't mean it wont work. It might not work well enough, But its a start. I just check goodwill, value village, and yard sales until I find something that has possibilities. Just remember you will need a small amplifier to increase the output of a small noise cancelling circuit. It by itself wont have the power to be noticed in a noisy car.
ErikB52 years ago

To do this you need an old Noisebuster headset and a head unit with an RCA output for an amplifier (you can do it with other units but this is by far the easiest way). You will be limited to stereo. Take the Noisebuster and hook it up to the head unit using an RCA to headphone jack adapter. Take the headphones of the Noisebuster apart. Remove the microphone pickups and add a longer wire, placing one in the front and one in the back of the passenger cabin. Take the headphone speakers out and solder the leads to RCA jacks. Attach the jacks to an outboard car amplifier and route the amplifier's output to the car's speakers. The stereo will function normally aside from front to rear fade (though it could be accomplished with two units, or using only one set of speakers to do the noise cancelling but this would interfere with sound from the other speakers).

A DIY noise cancellation solution or one salvaged from a set of headphones has no hope of cancelling sound in a large open air environment like a car. They are not powerful enough and stacking multiple systems together can't fill that void either.

High end cars do way more to reduce noise than other cars do. Not only is the interior well insulated, voids in structural aspects of the vehicle are often filled with foam, and the overall build quality is more precise reducing the vibration of parts. Only when measures like these are taken can a sophisticated noise cancelling system be of any use. It's a matter of having microphones placed in more key areas than just the wheel wells. You'll need one in each door, a couple for the trunk, couple for the engine fire wall and one on each wheel well. All that information will need to be processed so the proper waveform can be generated and delivered through the car stereo speakers.

In the end there are much better ways to reduce noise. It's much cheaper to buy car audio sound boards to help insulate the inside of the car to reduce noise. This stuff make a huge difference even if you only like the floor of the car with it.