Ah, the sweet sounds of the doppler effect – The rotating Leslie speaker design has a unique way of giving sounds a sort of warm temporal quality. There are many electronic simulations attempted but designing and building actual mechanical effects is plain awesome.

Update:
As a commenter pointed out – the above video doesn’t reflect the design of a true Leslie speaker, but a DIY variation. For more info and an exploration of the original design, check out this page on theatreorgans.com –
Leslie Diagram
UNEARTHING THE MYSTERIES OF THE LESLIE CABINET

From the pages of MAKE:
Rotary Speaker
Spatial Education MAKE:05, p.24 Subscribers – read this article now in our digital edition