Hello. I am trying to build a version of a Chladni plate, which is a device that uses a modified speaker assembly to mechanically resonate a dish containing salt or some other powder. When the input signal reaches the resonant frequency of the plate, crazy patterns start to appear in the salt. I have everything I need to create the physical device, but I am baffled as to how I can create a sinusoidal signal that I can easily modulate. I do not want to buy a signal generator, and so I am curious if there is a free program where I can generate a sinusoidal signal on my computer (preferably that I can easily adjust the frequency of with sliders) Also, I plan on using two 8 Ohm, 2 Watt speakers. Do I need to purchase some sort of amplifier? If so, what specifications should I look for? Thanks and happy holidays.