How Cat-Ears Work

When a fluid flows around a solid body, the fluid flow can become chaotic and rotational.  You can see this in the wake of a boat.  This kind of flow is known as turbulent flow.  Air is a fluid and, even though you can't see it, will behave in the same way when it encounters a solid object in motion.  Under certain conditions, air flow around a solid body will create rapid pressure changes we perceive as sound.  Common examples are wind instruments and blower-style hand dryers.

Cycling causes air to flow around our body, as if we were stationary during a windy day.  As the air flows around our head and the air stream impacts our outer ear, turbulence is created, and parts of that turbulent flow create sound that we perceive as wind noise. The physics of wind noise are a very complicated combination of aerodynamics and acoustics, appropriately known as aeroacoustics. Below is a photograph of turbulence created as water flows over a human ear model.

(UV laser lit fluorescein dye injection, 7 MPH air speed equivalent, Cat-Ears hydrodynamic flume)

Cat-Ears are engineered to reduce wind noise by modifying airflow.

Cat-Ears are fabric devices that attach to the leading straps of a helmet and deflect the air stream as it flows along the temple in front of the external ear.  But simple deflectors are not very effective at reducing wind noise, and can actually create noise themselves.  The key is in the shape and the material used.  Our design is able to divert the air flow while at the same time reducing the turbulence that causes the pressure changes we perceive as wind noise.  They don't eliminate all wind noise, but they reduce it substantially.

Sound pressure level data from Cat-Ears NJ open jet quiet wind tunnel runs using CATs test heads with in-ear microphones and FFT analysis

The plot above, taken from one of a great many tests, demonstrates the effectiveness of the Cat-Ears AirStreamz™ in reducing wind noise. We recorded wind noise at 16 MPH, with and without Airstreamz.  With Airstreamz, wind noise levels are reduced by about 15 dBA between 20 and 20,000 Hz (the maximum range of human hearing).  This is a reduction in overall measured sound pressure level of over 80%.  But microphones and ears behave differently.  This level of SPL reduction will, on average, be perceived by a human subject as a 65% reduction in noise loudness.

Hear the difference at 16 mph / 26 kph

Wind Noise without Cat-Ears - @ 16 mph
00:00 / 00:00
Reduced Wind Noise with Cat-Ears - @ 16 mph
00:00 / 00:00

Hear the difference at 22 mph / 35 kph

Wind Noise without Cat-Ears - @ 22 mph
00:00 / 00:00
Reduced Wind Noise with Cat-Ears - @ 22 mph
00:00 / 00:00

Wind noise at moderate cycling speeds can easily reach a sound level of 85 dBA, at which point all cyclists will experience severe masking of desired sounds - like that of the rider next to you, or the vehicle overtaking you from behind.

Because they do not cover the external ear, Cat-Ears have zero impact on sounds approaching the ear from all directions except straight ahead.  They are made from a material that is largely transparent to sound at frequencies below 7000 Hz, as shown below, and thus have a small attenuation effect on high frequency sound coming from straight ahead.  Cat-Ears are an aerodynamic device that does not block sound, enabling the cyclist to hear desired sounds such as that of an approaching car.

Sound pressure level data from Cat-Ears acoustic tests using sweep frequency generator and FFT analysis

Sound pressure level data from Cat-Ears acoustic tests using sweep frequency generator and FFT analysis

It is the nature of wind noise that while average noise levels dependably rise with increasing speed, instantaneous levels are highly variable and unpredictable.  You experience this as a "buffeting" noise.  You can see that on the waveform chart below, showing wind noise sound pressure levels vs. time at a constant 15 MPH (red without Cat-Ears, black with, as measured in our testing).

Time in seconds

Time in seconds

SPL

Sound pressure level vs. time  data from Cat-Ears road tests using in-the-pinna microphones

Beyond the obvious challenge of understanding and controlling a complex and chaotic physical process, further complications arise from the physiology of human hearing.  Human outer, middle, and inner ears are unique, as are head shapes, as is the way our brains process sound, with the result that no two people experience wind noise the same way, even in the same place at the same time.  

Add in the considerable influence that cycling accessories like helmets and glasses have on air flow, and you have a rather intriguing technical challenge in combating cycling wind noise.

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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.

Cat-Ears, LLC

PO Box 21

Cedaredge, CO 81413

970-856-1151

admin@cat-ears.com

 

Mon - Fri: 9:30am - 4:30pm | ​​Closed Saturday and Sunday

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