FRFR stands for - Full-Range, Flat-Response.  

The HeadRush FRFR speakers reproduce your sound with a full frequency range, and a completely flat response so you can hear all the details of the pedal and amp emulations coming from your Pedalboard, Gigboard, MX5, or other guitar FX processors. Whatever you connect, you can be sure the FRFR speakers will be honest and accurate to the sound source with no additional coloration.