Stereo system 4 channels 6 loudspeakers 2 mid-range loudspeakers, front 100 mm2 mid-range loudspeakers, rear, 100 mm2 bass loudspeakers, 160 mm Bandwidth: 50 Hz to 14,000 Hz Max. acoustic pressure 98 dB Amplifier power: depends on radio, radio: 4 x 15 W (4 Ω) M-ASK: 4 x 40 W (2 Ω) CCC: 4 x 25 W (2 Ω) HiFi-System (option 676) 6 channels 10 loudspeakers 2 treble loudspeakers, front 26 mm2 mid-range loudspeakers, front 100 mm2 bass loudspeakers, 217 mm2 mid-range loudspeakers, rear, 100 mm2 treble loudspeakers, rear 26 mm Bandwidth: 40 Hz to 20.000 Hz Max. acoustic pressure: 104 dB Amplifier power: 2 x 40 W (2 Ω) Bass 4 x 25 W (2 Ω) Top-HiFi System (option 677) on E90 9 channels, 13 loudspeakers 1 mid-range loudspeaker, middle, 100 mm2 treble loudspeakers, front 26 mm2 mid-range loudspeakers, front 100 mm2 bass loudspeakers, 217 mm2 mid-range loudspeakers, rear door, 100 mm2 mid-range loudspeakers, rear shelf, 100 mm2 treble loudspeakers, rear shelf, 26 mm Bandwidth: 30 Hz to 20.000 Hz Max. acoustic pressure: 110 dB Amplifier power: 2 x 70 W (4 Ω) Bass 7 x 40 W (2 Ω)