Where does it come from? How loud is it? And most importantly, what can I do about it?
In our previous post, we pointed out the extreme sound pressure levels (SPL) that are generated with increasing speed, and how they can permanently damage your hearing.
At high speeds, the bulk of noise you experience inside your helmet is so-called “aero-acoustic” noise. This means it arises as the result of the aerodynamic forces that are slamming into your helmet as you traverse through the atmosphere. Many people call this buffeting sound “wind noise”.
The figure below is a frequency plot of the noise signal recorded at the ear inside a Shoei GT Air helmet on a BMW R1200RS at 75 mph (120KPH). Note that the peak power in this signal is around 100 Hz – this is the rumbling “roar” that you experience when riding without hearing protection.
In the above graph, we have drawn a horizontal line around 30 dB down from this peak, which indicates that the vast amount of energy in the helmet noise spectrum falls between 15 Hz and 400 Hz.
We eliminate the noise in this narrow frequency range, which significantly reduce the Sound Pressure Level reaching the ears of the rider.
So how do we go about reducing this noise?
For the answer to this question, read on to the next blog post…
