Listening to these meditations through any sound system, even a phone speaker, will work fine if you follow along to the guides provided. However, for an optimal experience, it is best to listen using comfortable headphones. This will allow you to fully take advantage of the encoded binaural beats that make use of stereo sounds to work properly.
When using headphones, it is a good idea to use ones that are particularly comfortable to wear for long periods of time. It is also important to make sure they are securely fitted so they don’t fall off halfway through.
Headphones should never detract from the experience or be a distraction. If this is the case, you are better off listening through a speaker of some kind.