Dayton Audio RS225 - 8 measurements.
Not all high performance loudspeaker have to cost a fortune. The Dayton Audio RS series is one such line with the RS225 being one of the most used and cost effective bass drivers on the market.

It features a stiff aluminium cone, so before it goes through any kind of break-up acts as a pure piston, shorting rings for reducing inductance and lowering distortion and a very nice amount of linear excursion. This makes it perfect for the bottom end of a three way loudspeaker. Not only is it inexpensive but it measures like a champ and goes low when in the right box.
The measurements above were taken in a very small sealed box of aroundn 12 litres net volume.

The first image was taken at a drive level of 2.83VRMS or 8V peak to peak, equal to around 1 watt into a resistive 8 ohm

The lower image was taken at  20 volts peak to peak corresponding to a level of  ~95dB.

It should be clear why these drivers are so frequently used as to better them you really have to look to Scanspeaks revelator line, which are in a different price category completely.