Is it possible to calculate the energy required to speak a word?
For animals to check the amount of energy used for a certain behavior you can use a RESPIROMETER. It basically calculates the oxygen consumption.

In your case you could calculate for writing a sentence vs speaking the same sentence.

Regarding your second question:
At least in birds more than the type of sound (the frequency modulation) what matters for energy consumption is the amplitude --> how loud is your sound.