I understand what you are referring to.
For humans, the "voice in your head" can refer to the internal monologue or the stream of thoughts and self-talk that occurs within one's mind. This internal voice doesn't have a physical sound like an external voice, and its perceived volume tends to remain consistent because it's a mental phenomenon rather than a literal auditory experience.
The perceived volume of the internal voice may be influenced by factors such as the intensity of emotions, focus, and attention on a particular thought or idea. For example, during moments of heightened stress or strong emotions, the internal voice might feel more intense or intrusive.
While the internal monologue can vary in tone, speed, and content, it doesn't follow the same principles of physical sound, and thus, it is not experienced at different volumes like actual external sounds heard through the ears.