Help find model of this box

[GM]

So what do those 56 feet mean? Is the JBL table wrong? Explain it to me please. That my limited intelligence can understand it, please.

'Sound is round', so with a SoS = ~1130 ft/sec, the circumference of a 20 Hz sound 'bubble' = ~56.5 ft, ergo its diameter is ~17.9 ft, so oscillates 20x over a [3] diameters distance in one second.

GM