How to Hear Better in the Car


Hearing in the car is a challenging listening environment for people with hearing loss. The signal to noise ratios are less than optimal for maximum speech understanding. Moreover, conventional directional microphones are typically oriented for face to face communication which is not ideal when communicative partners are seated side by side or behind. Binaural directional microphones which can add an additional 3-4 dB of SNR improvement definitely require a face to face orientation in order to work properly. Finally, one cannot take advantage of lip-reading cues, especially if one is the driver. At night, the lack of adequate lighting negates the use of lip-reading cues for the passenger as well.

The noise levels generated inside an automobile can vary greatly by type of vehicle and the speed the vehicle is traveling. There are several websites available that list the interior noise levels of various automobiles. The data in the chart below, taken from http://www.auto-decibel-db.com/, is a sampling of several vehicles operating at various speeds.Noise Levels in Car

As you can see the noise levels can vary as much as 12 dB. Typically high end gas powered luxury sedans tend to have the lowest interior noise levels, while entry level automobiles and diesel cars tend to have higher noise levels. If we assume that speech is typically 65 dB in intensity, what then are the signal to noise ratios? In the table below, I have simply subtracted the measured noise levels from the 65 dB speech levels to obtain the SNR.

Noise levels in car 2 SNR

The next thing we need to consider is what SNR’s do people with various degrees of hearing loss need in order to communicate effectively. Below is the classic Killion data showing SNR’s as a function of hearing loss. Note that this is data for a typical adult. Children need higher SNR’s as do many geriatric clients. It is therefore ideal to actually assess a client’s speech in noise capabilities through a test such as the Listening in Spatial Noise Test – Sentences with the Prescribed Gain Amplifier, otherwise known as the LiSN-S PGA.

Noise levels in car 3 SNR Needed

Let’s look at a couple of examples of how to apply this information. The first example is a 40 year adult with a moderate sensorineural hearing loss. This gentleman owns a Honda Civic and frequently drives on highway of speeds 100-120 KM/hr. He is usually is driver rather than passenger Our chart indicates that the SNR at 100 km/h would be -1 dB and the SNR at 120 km/h would be -3 dB. The Killion data suggests that he will requires a SNR of at least 6 dB in order to understand speech. Which technology will work for him?

First there are conventional directional microphones that can only pick up speech from in front of the listener. This will of course not work in a car since a driver must face the road whilst driving and not the talker beside. Some hearing aids have the capacity to shift the directionality of the microphones to the side and in some cases stream the signal to the other side of the head that does not have an optimal microphone placement. The signal to noise ratio improvement that can be obtained from this arrangement is still the same as conventional directional microphone and is about 4-5 dB. This will be satisfactory for speeds up to 80 km/h, but not higher speeds.

What about a binaural directional microphone? Hearing aids with these features combine all of the microphones on each hearing aid to achieve an SNR of 8-9 dB. While this certainly fits the SNR criteria numerically, it will not work in this case as he is frequently the driver and must keep his head facing the road. Binaural directional microphones work in front only.

The final options are remote microphone technologies such as Bluetooth or FM (non-adaptive) or adaptive digital remote microphone such as the Roger microphones from Phonak. Since Bluetooth remote mics provide about a 10 dB improvement this will certainly meet the criteria.

But what happens if one needs a higher SNR or there is a need to hear multiple talkers? This is certainly the case with the next example. This is a 38 year old mother with two children. She frequently needs to drive her 2 children or her elderly parents to various appointments in her Ford Focus. She presents with a moderate-severe sensorineural hearing loss and the LiSN-S PGA results were in the red zone indicating that she needs SNR boosts of at least 15 dB. In this client’s case she could use a non-adaptive remote Bluetooth remote microphone for local 50 km/h city roads as this will improve the SNR from about 7 to 17 dB.   However, she will still experience difficulties hearing multiple talkers and at highway driving speeds. The only technology that can cover all of her driving listening needs would be an adaptive digital remote microphone.

Below is a picture of a set-up that I have commonly used for these situations. In it you see both communication partners using adaptive digital remote microphones that switch automatically between the talkers.  In this picture, we are using two Phonak Roger Pen transmitters.  These transmit both the talkers voices to receivers connected to hearing aids or cochlear implants.

Noise levels in car 4 Two Mics Pic

In summary, I would recommend that you and your hearing care professional look at the following critical pieces of information:

  1. What car do you drive ?
  2. Are you typically the driver or the passenger?
  3. Do you do a lot of highway driving?
  4. Do you need to hear multiple talkers?
  5. How do you perform on a Speech in Noise test.

Only when you have all the relevant information can you determine the best solution for listening in a car.

 

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6 thoughts on “How to Hear Better in the Car

  1. Hi Peter, this is an excellent review of the relevant factors at play during a typical road trip. Thank you so much for the analysis of the factors and how to improve a difficult listening environment.

  2. Hi Peter,
    That is an interesting analysis of car noise. Please allow me to add that car noise is not purely quantitative. It has a unique, continuous drone characteristic which comes from engine and road noise, I found that the algorithm for speech envelope recognition as in the higher end Oticon products, and probably many others, worked extremely well to allow hearing your passenger whilst driving. I have otosclerosis and single sided deafness which put my hearing side on the opposite side of the passenger. Such technology was put to good use. However in those days I was also a musician which meant that the technology which was so useful in the car had to be switched off in the music environment. Not a problem because a switch was provided for this very purpose. If it was forgotten to switch over then some very interesting results would be heard. A quick noisey blast from the trombone would result in a few hundred milliseconds of no sound afterwards until the speech envelope recognition decides there is no more trombone “speech”.
    I have been speaking in past tense because a few years ago my otosclerosis had spread in my only good ear to involve the round window rendering me almost profoundly deaf. With sensorineural loss in beyond the measuring capabilities of the audiological equipment and bone conduction way down I decided to go for the cochlear implant. I can now hear recognisable sounds which I can’t ever remember hearing before but speech is still very much a challenge and requires visual clues. As for music, The pitch changes between what I used to hear and what I now hear are very difficult to get to grips with so sadly I have given up on that.

    • Thank you Terry for your thoughtful comments.

      A few words on circuitry approaches to noise reduction. Generally speaking, most, if not all, hearing aids have some sort of noise reduction circuitry. The hearing aid can distinguish some noises from speech by analyzing frequency of the noise and certain temporal characteristics. So they can determine if something is steady state like a car or fridge hum compared to speech. When it finds this, it will reduce the amplification in the frequency region in which it occurs.

      There are some flaws to this approach to noise reduction. First, any speech sounds that were in the particular frequency band are also reduced. Second, the signal to noise ratio didn’t really change much, by the perception of the annoying noise is reduced. This is why hearing aid companies still have this feature in the hearing aid since it enhances comfort. But it must be used carefully, such that you only allow the noise reduction to occur in frequency bands where there is little of no speech content. To date, there has been no empirical evidence that these circuitry approaches improved speech perception scores in noise.

      On the other hand, there is well documented evidence that directional microphone and remote wireless microphone technology truly increases the signal to noise ratio and in turn increases speech perception scores. This is pretty much every hearing aid company has focused their efforts on directional microphones and wireless mics. Even in the wireless microphone world, there are differences in performance. Non-adaptive digital microphones such as Bluetooth microphones are a step up from directional microphones on the hearing aid itself because the microphone is closer to the talker’s mouth. The next step up would be adaptive digital directional microphones such as the Phonak Roger microphones. These constantly measure the room noise and send a signal to the receiver attached to the hearing aid to increase its internal gain. Now when this louder signal goes into the hearing aid, the hearing aid will apply lower amount of amplification since this signal is already louder. Any sound coming into the hearing aid microphone is also applied this lower amount of hearing aid gain. Voila, the signal to noise ratio is increased even more. At this time, there is no technology that increases the signal to noise ratio as much as an adaptive digital microphone such as found in the Phonak Roger systems.

      I am happy to hear that you have been getting benefit from your cochlear implant. We are so fortunate to be living in countries that can afford to provide us with such a helpful technology. When combined with a wireless microphone, you have a winning combination.

      Your comment about music perception however is not uncommon. Its tough for many people, I think I got lucky. I also feel that learning to play a musical instrument (I play bass guitar reasonably well, and can play a little piano, guitar and trumpet) combined with knowledge about musical theory has helped me appreciate music still. The use of a hearing aid in the non-implanted ear also helps for music perception, although this is not an option for everyone.

      • Hi Peter,
        The CI I have is from AB and I took the offer of the ‘T’ mic option. As I’m sure many are aware this microphone is positioned in the ear at the entry to the canal (external acoustic meatus) which is the focal point of sound caused by the shape of the ear lobe. This is the ideal place to site the microphone because it takes advantage of the natural directional selectivity of the ear. When I first used it the wow factor was there. I could much better tell from which direction the sound was coming and by turning my head a little I could localise different sounds. This has the effect by default of improving the SNR. Although the ‘T’ mic has so many advantages, it would be a bit of a technical challenge to fit it to a normal hearing aid. Unlike the normal hearing aid, the CI has no acoustic feedback path. I agree with all your comments about microphone technology and its effect on differentiating between sounds and thus improving our voice/noise discrimination. It’s good to know there are other like minded people in the world.

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