Hearing / Safety

"It has been said that 'the purpose of the ears is to point the eyes.' While the ability of the auditory system to

 localize sound sources is just one component of our perceptual systems, it has high survival value, and living

 organisms have found many ways to extract directional information from sound."  (ECE Dept., UC - Davis)

While we are not Audiologists, we have read extensively about hearing impairment and noise annoyance / fatigue. 

 

On this page, we share hearing and hearing impairment information from highly respected sources. In our opinion, and based on the information presented below, we believe that Wind Noise can create a safety issue for many cyclists. Given the frequent discussions and proposals to improve cycling safety - and attempts to increase participation, we view Wind Noise reduction as an extremely easy and inexpensive way to significantly improve road cycling safety. Comments and feedback are welcome.

 

We believe the information presented below is accurate and up-to-date... related citations are, of course, included.

Summary Wind / Turbulence Induced Noise Data

 

The two charts below (Wind Noise vs. Speed and Wind Noise Spectrum) are based on data accumulated by Cat-Ears.

 

U.R. Kristiansen and O.K.Ø. Pettersen* measured Wind Noise under controlled conditions. Through flow visualization and aerodynamic pressure measurements they found that the relatively high noise heard when looking directly into a wind has its origin in wake flow fluctuation created by flow separation at about the position of the cheekbone. The average person facing a 21 mile per hour wind experiences noise within the range 25 to 150 Hz at an intensity of 92 dB.  *Experiments on the Noise Heard by Human Beings when Exposed to Atmospheric Winds, University of Trondheim, Norway, 1978

 

=>  At moderate cycling speeds (~12 mph to ~18mph), Wind Noise can easily exceed 85 dB

 

=>  The Wind Noise Spectrum is predominantly low frequency - similar to road and traffic noise

Wind Induced Noise

 

CE Road Test Data (~10 to ~25 mph)

>5,000 calibrated / accumulated data points

(perceived Ear-Wind Noise can vary from recorded

 - and perceived Wind Noise varies from person to person)

Wind Induced Noise Spectrum (20 to 20k Hz)

 

Smoothed Fast Fourier Transform (FFT)

 CE Road Test Data (~5 to ~25 mph)

(amplitude variation averaged

- hertz distribution similar

 across wind speeds)

Wind Noise Impairs Your Ability To Hear Surrounding Sounds

Signs or Symptoms of Impaired Hearing

 

  • Loss of directionality of sound (source / localization)

  •  Speech discrimination difficulties - 'cocktail party effect'

  •  Sounds or speech becoming dull, muffled and attenuated

  •  Frequently asking others to speak more clearly and loudly

  •  Need for increased volume (audio players / comm devices)

  •  Feeling tired or stressed from concentrating while listening

Different Noise (dB) Levels and Effect

Summary Descriptions

(Wind Noise Induced Threshold Shift)

 

Moderate Impairment / Shift:

Soft and moderately loud noises are not heard

Understanding normal speech becomes more difficult

 

Severe Hearing Impairment / Shift:

  Conversations have to be conducted more loudly

Group conversations are possible with considerable effort

Sources:​ ​Mayo Clinic, American Academy of Audiology,National Institute on Deafness and Communication Disorders

Different Degrees of Hearing Impairment

Speech Intelligibility is Affected Adversely by Wind Noise

 

To achieve full sentence intelligibility for listeners with normal hearing, the signal to noise ratio – the difference between the speech level and the sound level of the interfering noise – should be at least 15 dB(A).

 

The nature of speech sounds determines the mechanism of loss of speech intelligibility. Vowels and consonants convey different sound energy. Consonants are spoken more softly than vowels, and tend to get drowned out in noisy environments. The average level of consonants is 10 – 12 dB lower than the level of vowels.

Beaufort Wind Scale (Strong Breeze): 7.6 - 9.7 m/s (17 - 22 mph)  Effect on People  =  Wind Noise on Ears Unpleasant

(The scale was devised in 1805 by Francis Beaufort (later Rear Admiral Sir Francis Beaufort), an Irish Royal Navy officer)

Range of Audibility of the Human Ear (~20 to ~20,000 Hertz)

 

The range of human hearing extends from frequencies of around 20 to around 20,000 cycles per second. The figure below shows the range of audibility of the human ear for different frequencies. The lower curve, the Threshold of hearing, represents the lowest intensity level at which sound waves of various frequencies can be heard. The upper curve, the Threshold of pain, is the intensity level above which a sound produces discomfort or pain.

Most Wind Noise occurs below 1,000 Hertz

These sound files have been provided by the Danish Information Center for Hearing Impairment and Deafness, Delta Akustik and Vibration.

Age Related Hearing Loss / Presbycusis - Slow Loss of Hearing

 

Even if we avoid exposure to very loud noise, the ear's outer hair cells may also simply wear out as we age, leading to age related hearing loss. In this condition, high frequency outer hair cells tend to die off before low-frequency ones, possibly because the high frequency outer hair cells have to work harder if their job is to amplify acoustic vibrations on a cycle by cycle basis. Consequently, individuals with age-related hearing loss often have normal sensitivity at low frequencies, but progressively poorer sensitivity for higher frequencies, as shown here:

Source: Olsen, Dr. Harry F. Modern Sound Reproduction, Huntington, N.Y. : Krieger Pub., 1978.

Our hearing tends to deteriorate with age, but not equally across the frequency spectrum. Hearing deteriorates more rapidly at the mid and higher frequencies. 

 

The loss of higher frequency hearing as we age means that we are increasingly dependent on lower frequencies (<1,000 hertz) for communications and situational awareness ques.

 

As we age, our hearing tends to become

proportionately more acute at low frequencies.

Wind Noise Masking The Sound of Approaching Cars and Trucks

The noise generated by a vehicle can be classified into three general categories: the power unit noise (engine, fan, exhaust and the transmission, etc.), the aerodynamic noise, which is related to the turbulent airflow around the vehicle, and the tire/pavement noise.

 

The power unit noise and the tire/pavement noise are the important sources of noise levels for roadside noise. The speed of the vehicle also affects the noise level. This chart shows the effect of speed on noise. This figure presents the national average as used in the FHWA’s Traffic Noise Model (TNM).

Sources: U.S. Department of Transportation - Traffic Noise Model

European Environment Agency (EEA) Copenhagen, Denmark

Auditory (Wind Noise) Masking - A Brief Introduction (see links to learn more)

Auditory masking refers to one sound covering / masking another

(making it virtually impossible to hear the sound being masked)

 

Auditory Masking is a reduction in the ability to detect, discriminate, or recognize a specific sound (the signal or target) due to interferences caused by another sound (the masker). This is measured as an increase in the detection threshold caused by the masker. The amount of masking is represented by the increase in threshold measured in decibels (dB).

In general, low sounds mask higher sounds and there is a spread of the masking effect upward in frequency as the intensity of the masker is increased. By way of transduction, the basilar membrane in our inner ear vibrates in response to sound. Low frequencies displace the basilar membrane much more: the distance from stapes (one of the three bones in the middle ear) is about 30mm at 25 Hz compared to 20mm at 800 Hz. Additionally, as frequency increases, the location of maximum displacement along the basilar membrane moves from the farthest section of the inner ear (helicotrema) toward the middle ear (to the stapes and the oval window). Higher frequencies must therefore be of greater intensity to overcome the dominance, both spatially and quantitatively, of the low notes over the basilar membrane. (Sources: Masking and Perceptual Coding - NYU, AAA, Auditory Neuroscience - MIT)

Noise Annoyance / Stress - Symptoms and Health Issues (see links to learn more)

 

"Noise can trigger both endocrine and autonomic nervous system responses that affect the cardiovascular system... These effects begin to be seen with long-term daily exposure to noise levels above 65 dB or with acute exposure to noise levels above 80 to 85 dB.... to place this in context, 85 dB is roughly equivalent to the noise of heavy truck traffic on a busy road."  Southern Medical Journal (excerpted from) WHO 

Discussion and Summary

 

  • Wind Noise can easily exceed 75 to 80 dB while cycling at moderate speeds - masking important sounds.

 

  • Hearing impaired individuals will have a spatial (sound source localization) processing deficit of some degree.

 

  • Loud noise(s), particularly variable noises, are distracting, interfere with concentration, and cause mental fatigue.

 

  • Since the external ear performs critical acoustic functions, Cat-Ears were designed to be acoustically transparent. 

 

  • Cat-Ears provide an easy / very inexpensive way to reduce Wind Noise and significantly improve road cycling safety.

Just as Blinders limit peripheral vision... Wind Noise limits a cyclists ability to hear peripheral sounds

Theoretical and Applied External Ear Acoustics - B. B. Ballachanda (Speech and Hearing Sciences, University of New Mexico)

Masking of Speech by Amplitude Modulated Noise - Gustafsson / Arlinger (Dept. of Audiology, University Hospital, Linköping, Sweden)

Experiments on the Noise Heard by Human Beings when Exposed to Atmospheric Winds - Kristiansen / Pettersen (University of Trondheim, Norway)

Auditory Neuroscience: Making Sense of Sound - J. Schnupp, I. Nelken and A. King, Masssachussettes Institute of Technology, Cambridge, MA, USA 

We have received many notes (e-mails / facebook comments) from cyclists / customers similar to this:

       

"I'm convinced that I have slight hearing loss in the frequency range that is the same as the wind passing your ears while riding / racing.

It may be mental, but I struggle to hear sounds within that range."  (MJ - Spain)

Below is a letter written by one of our customers to his cycling group regarding wind noise and hearing loss:

Dear Fellow Riders:

 

We all wear helmets to protect our heads, sunglasses to protect our eyes, and sun block

to prevent skin cancer. But we ignore our ears.

 

Since I recently ended up with partial hearing loss and tinnitus in one ear, my ENT doctor

warned that wind noise from cycling was damaging my ears. I found a graph, and sure enough,

we’re subjecting our ears to noise levels beyond the 85 dB threshold at which OSHA requires

protective headphones. My doctor explained that noise damage is cumulative over one’s lifetime 

- kind of like hitting a steak in the same place over and over until finally one day the meat gives

out. This is why hearing loss and tinnitus are an 'old persons disease'. One day you wake up and

you’ve got tinnitus and senso-neural hearing loss - and it is IRREVERSIBLE. Well, trust me, you

don’t want hearing aids and the constant 24/7 ringing in your ears from tinnitus. Protect yourself

while you still can. Don’t play Russian Roulette with your ears. It’s just not smart.

 

I searched the cycling forums and discovered several solutions. The “Cat Ears” were the least

intrusive and can cut wind noise by 20 db, so we bought some. I’ve ridden with them twice and

they are bloody fantastic. Not only do they cut back on the dangerous noise level, but I can now

hear cars and other people much easier... I can hear the hum of my wheels on descents where

previously all I got was wind noise in my ears. These attach to your helmet strap and work on

the principle of the fur in a cat’s ear. Have a look at the website: http://www.cat-ears.com/

 

Regards, Tom (California)

Any sound level about 85dB is damaging over an 8 hour period. For every 3dB of sound over 85dB, the maximum permissible exposure time is restricted to half. For example, 88dB of sound is damaging over 4 hours of exposure, 91dB of sound is damaging over 2 hours of exposure, etc. At these levels ,the cyclist is not only fatiguing physically from the excess noise exposure (commonly referred to as 'noise fatigue'), but causing potential hearing related difficulties later in life. 

Cat-Ears / AirStreamz is the leading manufacturer of aero-acoustically designed passive wind noise reduction products for serious cyclists. Tested and recommended by respected publications and professionals, Cat-Ears / AirStreamz are the highest rated and best selling products designed for cyclists.  They are 100% Satisfaction Guaranteed and Made in the USA.

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