Yeah you did. Send them back if you can. Read the difference at the mfg site
http://www.m-audio.com
Here's the specs anyhow. You decide.
SP-5B Specs:
• Type: 2-way near field monitors
• Woofer: 5-inch driver with magnetically shielded mineral-filled polypropylene cone, high- temperature tolerant voice coil and damped rubber surround
• Tweeter: 3/4-inch swivel-mounted silk dome incorporating magnetic shielding, ferro-fluid and internal damping technologie
• Crossovers: 4th-order Linkwitz Riley
• Input Connectors: XLR balanced, TRS balanced/ unbalanced
• Input Sensitivity: 200 mV input produces full output with Input Sensitivity control at maximum
• Input Impedance: 30k ohms balanced, 15k ohms unbalanced
• Protection: RF interference, output current limiting, over temperature, turn-on/off transient, subsonic filter, external main fuse
• S/N Ratio: > 100dB below full output, 20kHz bandwidth
• Frequency Response: 48Hz - 22kHz
• Crossover Frequency: 2.7kHz
• LF Amplifier Power: 42W
• HF Amplifier Power: 33W
• Indicator: Power On/Off indicator on front panel
• Power Requirements: Factory programmed for either 115V-50/60Hz, 230V-50/60Hz or 100V-50/60Hz; Power via detachable 3-circuit line cord
• Dimension: 9.85 in. (h) x 6.54 in. (w) x 7.88 in. (d)
• Shipping Weight: 28 lbs./pair
SP-8B Specs:
• Type: 2-way near field monitors
• Woofer: 8-inch driver with magnetically shielded mineral-filled polypropylene cone,
high-temperature tolerant voice coil and damped rubber surround
• Tweeter: 1-inch swivel-mounted silk dome incorporating magnetic shielding, ferro-fluid and internal damping technologies
• Crossovers: 4th-order Linkwitz Riley
• Input Connectors: XLR balanced, TRS balanced/ unbalanced
• Input Sensitivity: 200 mV input produces full output with Input Sensitivity control at maximum
• Input Impedance: 20k ohms balanced, 10k ohms unbalanced
• Protection: RF interference, output current limiting, over temperature, transient on/off, subsonic filter, external main fuse
• S/N Ratio: > 100dB below full output, 20kHz bandwidth
• Frequency Response: 33Hz - 22kHz
• Crossover Frequency: 1.8kHz
• Low Frequency Amplifier Power: 55W
• High Frequency Amplifier Power: 45W
• Indicator: Power On/Off indicator on front panel
• Power Requirements: Factory programmed for either 115V-50/60Hz, 230V-50/60Hz or 100V-50/60Hz; powered via detachable 3-circuit line cord
• Cabinet: Vinyl-laminated MDF
• Dimension: 14.97 in. (h) x 9.5 in. (w) x 11.82 in. (d)
• Shipping Weight: 57 lbs./pair