Royal Rife frequencies 20Hz and 10000Hz are believed to have many healing effects on human body as discovered by Dr Royal Rife in 20th century.
20Hz is one of the top Rife frequency which can cure many deceases compared to other rife frequencies – so called Cure All frequency. It is the beginning of the human audio spectrum so our ears cannot hear it properly also many speakers/headphones cannot reproduce it correctly.
So here 1000hz mixed with 20hz in isochronic mode so that our brain will differentiate 20 Hz too and get benefits of both frequencies.
Since it is isochronic tones headphones are not necessary. You can listen it with a good speaker at normal volume.