hz/khz use the metric system so 1kz = 0.001hz (10 to the power of 3)

in other words 20,000hz = 20khz

and I have yet to hear a system (get it?) that is capable of:
mhz: 10 to the power of 6
ghz: 10 to the power or 9
thz: 10 to the power of 12

Only a child will hear 20-20,000hz so unless your playing to a very young audience you might as well use the JBL's