I found this graph at Izzy Wizzy's Acoustat site
The response looks remarkably flat, however you may notice a declining average response (with peaks) below 500 Hz (my speaker does that too) and roll-off starting almost precisely at 14kHz (as I have found).
Acoustat specified a "18kHz" upper frequency. That seems close enough to 20k for most people. By normal standards, that would mean -3dB at 18kHz. That pretty much fits the above graph, though it could be more like -6dB depending on where you put the 0dB point.
But what we really might have wanted was flat response to 20kHz, with rolloff to -3dB at, say, 30Khz.
I've seen an interesting argument that we need flat response to wherever (say, 20kHz) even if the recordings and ears roll-off before that. One reason is that the speaker rolloff adds to the recording rolloff (and every other rolloff) making it sound audibly deficient, even if every one of these rolloffs is inaudible by itself. Well this is pretty obviously true, but we often don't think of this when we are presented frequency response specifications, or think that we don't need a speaker with response above 16kHz because we can't hear 16kHz tones.