• How can you amplify the sound at the ear so that it seems twice as loud - without any electronics?
• What is the smallest difference between the two ears that you can hear?
• And what happens if you swap the ears?

You can find out these and other questions about hearing with two ears for yourself at the "inverse hearing throne" - open 24/7 in front of the Nessy building of the University of Oldenburg at Küpkersweg 74!

Prof Dr Dr Birger Kollmeier explains how it works in the video.

1. Exponential funnel: This funnel shape is familiar from the gramophone or trombone because it is particularly favourable acoustically - even if the funnel is operated the other way round in the listening throne: The sound incident on the large input surface of the listening funnel is transmitted to the small surface at the output. This works best - and with the exponential form with the lowest losses - at high frequencies. In the case of the ear trumpet, the surface area is reduced by a factor of about 100 - and the sound intensity is increased by the same factor, which corresponds to a gain of 10 dB. This is almost exactly a doubling of the perceived loudness - so everything sounds twice as loud with a listening throne! Please try it out!
   
2. Variable distance between the ears: Humans have an ear distance of approx. 16 cm and can resolve an angular difference of approx. 1 degree - this corresponds to a time difference between the ears of just 20 µs (20 times the millionth part of a second), incredible!!! If the distance between the ears is increased, the time difference that occurs between the ears when sound is coming from a certain direction increases to the same extent: if we increase the difference between the funnels of the ear trumpet to ten times the ear distance, i.e. over 1.6 metres, we can therefore improve the smallest audible angular difference by a factor of ten! Please try it out!
   
3. Direction exchanger: If the sound is directed from the left side to the right ear and vice versa, we perceive the sound exactly from the opposite side: A car travelling from left to right past the inverse listening ear appears acoustically from right to left - a contradiction between acoustic perception (ears) and visual perception (eyes). This contradiction increases as the funnel distance increases - does the visual or the acoustic impression win? Please try it out!