There might be a few ways to do this depending on your goal or desired outcome. For example, if you are looking to ease stress with the use of the 174 Hz frequency, all you would need to do is evaluate yourself before and after listening.
Try writing down how you are feeling beforehand, and then write how you felt after. After a few sessions you can review what you have expirienced.
Your heart rate may also be a great indicator as to how you are being affected. Try recording your heart rates before and after listening!
It is all about the goal you are trying to achieve. If you are trying to better achieve active meditation, try listening to the Solfeggio Frequencies to aid in that process!