Constant Magnitude Chirp across audio band (Parseval's Theorem?)
If you change the "X = chirp(t,fo,10,f1,'logarithmic');" to "X = chirp(t,fo,10,f1,'linear');" you will get the response that you want.

To have the energy be equal it must spend an equal amount of time at each frequency.  With the linear sweep it does that.  With the logarithmic sweep it spends more time at the lower frequencies and much less time at the higher frequencies, resulting in unequal energy.