I've seen this topic you mentioned. But really didn't get this, they recomend a phone that answers starting from 18hz... so if they use a phone like that and it works, i thind 'ill not pay twice or three times the money just to get a phone that answers starting from 5hz ... Maybe this frequency they...

Hi! I'm about to buy a headphone to use with i-doser. But I have a doubt. Most of head phones i've seen to buy have a FREQUENCY ANSWER that starts from 20hz to 20.000hz .... some starts on 18hz ... some 10hz... and a few 5hz. I've seen the APPROVED headphones link on i-doser website... and that wire...