Transparent Slide Whistle Transparent Slide Whistle £7.99 Quantity: at £7.99 each Add To Basket 2 in stock. SLIDE WHISTLETransparent slide whistle with packaging designed to show children how sound works. Eg: A large chamber produces a low note, a small chamber produces a high note. The transparent tubeallows child to visualise the chamber size changing as the sound changes. Perfect for science projects.