Ignore anything above 200hz. This plot shows you the low end frequency response and the efficiency of several popular 7" drivers. Remember, some mids are 2 ohm, some 4 ohm, and others 8 ohm. Be sure to add 3db for every doubling of impedance, and subtract 3db for every halving. Also, keep in mind this is the actual driver's frequency response, not including room, box, etc.