helmholz resonator height

I'd like to build some helmholz resonator covering the walls in my studios recording room to get read of some low-mid problem (300-500hz). do i have to cover the wall till the ceilling (ca. 3.5m high) or is it enough if i go like 2-2.5 hight but cover the all wall length?

any height you like. :) cheers john

thanks John, now if i do the helmholz walls 2.5 m high what would you recomend to do with the rest 1.2m above (fill the gap with fiberglass cover with ply wood and use as panel traps, cover with textil and use as high freq absorber? or...)