Yeah that room just cancels reverberation so you cant hear an echo .... So if you scream itll sound like ur scream instantly ends when you stop i had a girl spend 8 hours in my tank spent the entire time awake too whats interesting is that our brain hates not receiving any stimuli from the senses so it makes crap up.... thats why when u are in a super quiet room late at night you start hearing a wierd buzzing sound or when ur laying in bed when its totally dark you start seeing colors swirling around .... That's ur brain keeping you entertained .... 
In the tank you wont know how long youve been inside after the first 10 minutesl