Do you find this believable? https://static-neumann.s3.amazonaws.com/global_images/image/file/461/KH420_pro_510.gif
It is not only believable it has been pretty much the standard for high quality, high fidelity speakers for the last decade or two in both commercial and DIY speakers. It is achieved by using an active crossover and setting it up during speaker assembly to compensate for the slight variations in the mechanical properties of the drivers. That is, each speaker is individually tuned to meet a target response (flat in this case) to within a fraction of dB typically. As the speakers age the process can be repeated to compensate for any slight drift in mechanical properties. Any modern expensive speaker that is not designed in this way is declaring a disinterest in high quality engineering and high fidelity performance (of course other factors like off-axis behaviour, adequate clean SPL,... are relevant as well).
It can sometimes be difficult to comprehend just how irrelevant high fidelity and good quality engineering has become in the weird marketing dominated luxury goods sector that home audio has become. For the price, domestic PMC speakers are poor-to-modest when judged against such criteria but such criteria are not highly weighted but purchasers of PMC products. And why should they be if PMC products provide what the purchasers actually want from their speakers?
The "Preaching Tolerances" section near the end of this review gives some details on the tolerances achieved at the factory in Ireland. A modern mass produced speaker affordable to enthusiasts that significantly weights good engineering and high fidelity should meet it's target on-axis response (probably flat but not necessarily depending on off-axis behaviour and/or compensating for stereo issues and/or room influences) to within +/- 0.5 dB. The days of +/- 3 dB are long gone except of course in the audiophile world!