9v inverter frequency

Hi Guys,
I just bought a 9v inverter and was curious if any of you knew how to change the output frequency. The story is: it is a 9VDC in 120VAC out inverter with a frequency of 4kHZ. I would like to be able to step down the frequency in intervals (e.g. 1000kHZ, 100HZ, 10HZ, 1HZ). I am not using this for any specific application so you guys can be as creative as you like. I am just using this as a learning opportunity. Thanks in advance.

To step down the frequency you would have to increase the inductance (hence physical size, weight and cost, in general) of the switcher inductor.