10-14 Hz are the most common and the least expensive. Much more than 20-30 Hz and you start cutting into your signal. Less than 10 Hz and the phones become a somewhat fragile and less field-robust.
10-14 Hz are the most common and the least expensive. Much more than 20-30 Hz and you start cutting into your signal. Less than 10 Hz and the phones become a somewhat fragile and less field-robust.