And here is Edwin Collingridge's DIY transducer project: http://www.xsimulator.net/community/threads/diy-tactile-transducer.6017/
In a unique approach @Alexey combines an amplifier and transformer to create a small but very powerful transducer : http://www.xsimulator.net/community/threads/diy-high-power-bass-shaker.7070/