Above 10 Hz, loudness grows 10 phon per tenfold rise in repetition rate.

Evidence

Up to a repetition rate of 10 Hz, loudness level remains approximately constant. For repetition rates above 10 Hz, loudness level increases by 10 phon if the repetition rate is increased by a factor of 10. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1237