The external ear (pinna and the ear canal) plays a major role in transforming acoustic signals from free field to the middle ear (tympanic membrane). It acts as a filter to reduce low frequencies, a resonator to enhance mid frequencies (2.0 to 7.0 kHz), and a direction-dependent filter to at high frequencies to to augment spatial perception. Consequently, the characteristics of sound reaching the middle ear from the free field are influenced by the physical dimensions and the response properties of the external ear.
According to Shaw (1975), the factors that govern the sound transformation from free field to the tympanic membrane can be divided into two major areas: (1) the head, torso, and pinna flange acting as diffracting bodies and (2) the concha and the ear canal acting as resonators.
Since wind noise is aero-acoustic, the amount experienced will also be influenced by the physical dimensions and response properties of the external ear. In addition, head shape, eye wear, facial hair, and helmet design can influence wind noise. And, just to make things more complicated, a persons ears (L / R) typically have some variation.
Ear Shape Variation
We obtained six different silicon ear sets designed for acupuncture training / binaural recording. We aeroacoustically tested these ears in our open jet wind tunnel to evaluate the wind noise generated by slightly different ear shapes. We eventually settled on two high quality ear sets (with desired variations) for ongoing wind tunnel testing.
Ear Canal Variation
Real 'in the canal' measurements using sound pressure probe tubes have helped us understand ear canal variation.
Head Shape Variation
Head shape can also impact experienced wind noise. However, pinna shape variations typically have a larger impact.
Based on our analysis of different ear / pinna and head variations, measured wind noise can vary by several decibels.
Related Reading / Scholarly Articles
Transformation characteristics of the external human ear
Theoretical and applied external ear acoustics (B. Ballachanda)
The pressure distribution in the auditory canal in a progressive sound field
Experiments on the noise heard by human beings when exposed to atmospheric winds
An average of the human ear canal: Recovering acoustical properties via shape analysis
On the relation between pinna reflection patterns and head-related transfer function features