The Future of Noise Reduction Inside Electric Vehicles

With the rise of all-electric vehicle manufacturers, like Tesla & Rivian, along with longtime, well-known OEMs like Volkswagon and GM making the switch to EVs, a new trend has become more prevalent. That is, without the sound of an internal combustion engine generating ample amount of noise, consumers are now complaining about the other sounds being produced by the road, mechanical components, and basically, anything loud making its way into the vehicle's cabin.

Currently, EVs carry a decent price tag when purchased brand new. With that comes the expectation of a luxurious ride. As self-driving cars become increasingly accepted and used by the public, time spent during a commute will begin to shift towards other tasks, such as conference calls, reading, and catching up on last night's emails.  So, let's look at the cabin of the vehicle as your own office...

Loud noises have become one of the greatest irritants in an office environment. One study showed that 99% of employees reported that their concentration was impaired by various types of office noise, like telephones ringing and people talking in the background. Researchers also found no evidence that people become used to these sounds over time.  Now imagine all the noises thrown at you while on your commute and how hard it's going to be to concentrate if EV manufacturers put a high amount of attention to reducing the amount of sound entering the vehicle's cabin.

We crave the uninterrupted focus spikes where we aren't distracted by constant sounds and annoying noise pollution.  We especially don't want to hear constant squeaks and rattles from all the little mechanical devices found throughout the vehicle.

Noise-cancellation works best with canceling out consistent noise.  This is because matching a sound wave is extremely difficult as you are only able to eliminate so many sounds at once.

To achieve a silent ride, you need a way of damping the sound from entering the cabin.  But, before we get into that, we need to have a better understanding of what exactly does sound damping mean.

Noise damping is a way of preventing vibrations on vehicle bodies and materials by converting the vibrations into heat.  It works by reducing energy stored in an oscillation.  The goal is to slow down an oscillatory system as fast as possible by adding noise damping materials into the system.  Reduction of the duration and size of vibration a vehicle experiences will result in a reduction in noise.

Using a thicker aluminum foil, they're able to achieve improved vibration damping and better heat control, as aluminum is excellent at dissipating heat fast. The added benefit here comes from helping reduce the amount of heat coming battery from entering the cabin.

Below is a simple demonstration of how it works to dampen the vibration and sound of a metal object.

What you can expect to see in future EVs in an increase in the overall usage of noise-damping mats for paneling and patches for panel holes. As well as an increase in the thickness of the butyl for improved damping performance.

Butyl Mat Acoustic Properties: Using the theoretical maximum loss factor is 1 (no vibration). An undamped 1mm thick steel panel has a loss factor of roughly 0.001 at 200 Hz. When a butyl mat/patch is applied to that panel, it increases the loss factor to 0.17 (performance varies depending on the temperature).

Above we listed just a couple of ways in which EV manufacturers are combating noise from entering the cabin.  But that's just the tip of the iceberg for this topic.  Here are few products being used already that have made a significant impact on in-cabin noise reduction. 

Sound insulation foam is used for several reasons. It's an excellent replacement to a vehicle's carpet padding. An open-cell bottom half makes a great method of absorbing sound and also great insulator from the heat that makes its way through noise-damping mats.  A close-cell foam top half makes a great way of sealing out liquids from penetrating deep in the vehicle's interior. 

Another benefit includes its ability to absorb the noise be produced inside of the vehicle. Imagine being on an important call and the person you're speaking to starts complaining about how loud the background is and the echos they can hear. Insulation foam works just like you'd imagine seeing in a recording studio to give a better acoustical performance.

Engineers behind tire tread designs continue to work towards developing a way of modifying the audible noise that a tire generates in order to get one step closer towards generating a more pleasant 'white-noise'.  Using pitch sequencing, engineers tinker with the different tread pitches and placements by aligning lateral grooves with adjacent tread blocks.  But will this be all that we see in the coming years or will there be a drastic change, such as the airless tires that are gaining momentum in adoption?  As technology continues to evolve, so will the results.

Time to start thinking about noise reduction outside of the car.  Studies continue to be put in place on reducing the sound coming from busy highway systems and one method has been implementing recycled tires that are mixed into the asphalt. This is also referred to as rubberized asphalt. Noise tests on rubberized asphalt have shown a 50%-90% reduction in noise.  This is huge! But this is just one way of reducing pavement noise. For example, researchers at the University of Notre Dame created a new method of grooving pavement to reduce highway noise even further. Check out their work here.

The increase in worldwide demand for electric vehicles has brought about unique opportunities for in-cabin improvements.  The future potential of these vehicles will become even more abundant as we begin the shift towards self-driving cars. 

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