C1-690 with 82-5607 adapter
Continuous Power Handling: 60 Watts
Recommended Amp Power: 10-100 Watts per channel (RMS)
Efficiency: 91.5 dB @ 1W/1m | 97.5 dB @ 1W/0.5m
Sensitivity: 94.0 dB @ 2.83V/1m
Nominal Impedance: 4 ohm
Frequency Response: 39Hz - 22 KHz ± 3 dB

C1-650x with 82-5605 adapter
Continuous Power Handling: 50 Watts
Recommended Amp Power: 10-75 Watts per channel (RMS) 
Efficiency: 90.5 dB @ 1W/1m | 96.5 dB @ 1W/0.5m
Sensitivity: 93.0 dB @ 2.83V/1m
Nominal Impedance: 4 ohm
Frequency Response: 48 Hz - 24 kHz ± 3 dB