Organ pipe in Cologne Cathedral

Here's the organ loft at Cologne Cathedral. I estimate the length of the biggest pipe as 5 metres based on the height of the balcony rail. Assuming an organ pipe to be a closed end pipe, that represents 1/4 of a wavelength. Wavelength would be 20 metres. Frequency = speed/wavelength = 330/20 = 16.5Hz. Problem is that it would be below the frequency that humans can hear!