A 10Hz beat is not heard as a pitch, rather as a fluctuation of volume, but it is certainly detectable.
As a seperate topic, a low tone from, say, an organ pipe may not be directly 'heard', but our brains deduce its pitch from its harmonics, which ARE audible. We deduce 'A low-low C will have harmonics including the C above then G, then the next C, E...etc. I can hear THOSE notes, therefore there must be a low-low C'. And, perceptually, we actually HEAR the low note! This phenomenon is used in pipe organs to avoid the cost of immensely long pipes. http://www.pykett.org.uk/resultantbass.htm