Frequency response + or - 1 dB ??

FWIW  Revel Salon specify +/- 1/2 dB from about 29 to 18,000. They are also the longest lasting reference level speaker that has remained unchanged. I find that interesting when most manufacturers seem to make changes simply to make a change. I think the Salon’s uniquely sculpted face also leaves little room for improvement in dispersion.  Also interesting as only B&W seem to also have a significant design to eliminate dispersion 

Ptss, you can make speakers pretty close to flat when tested in an anechoic chamber. There will be some unit to unit variation. The problem is that once you put them in a real room their response curve changes. The Japanese tried to design loudspeakers this way and they were awful. It is impossible for a speaker manufacturer to predict let alone compensate for the acoustic environment their speakers will be placed in. If you want to be assured of flat frequency response get headphones.

How do they, the various speaker manufacturers, measure frequency response? Do they use the same anechoic chamber? Their own anechoic chamber? Is there a standard for anechoic chambers? Or some other kind of specially constructed room? One wonders if they construct a room that produces a flat frequency response for a particular speaker, if you see what I mean.

Why is it hard to get flat frequency response, on axis, in an anechoic chamber? What is it about the drivers that needs “technical” improvement? We’ve put men on the moon, extreme precision required; what’s the big deal with loudspeakers. With the amounts charged for the “spensive” models — I expect better; more accuracy. 

My question is simple.
Why is it obviously technically difficult for speaker designers to provide precisely level frequency response. @kenjit. I accept some listeners want to adjust the sound for different recordings. Old fashioned tone controls and modern equalizers provide that.

Duke answered your question above.

How about because human ears are nowhere near as sensitive to amplitude as they are tone.

This is true and I find it amusing that in amplifiers the constant voltage characteristic is considered so important, when in the end, the ear actually places a greater value on the tonality caused by distortion than it does on tonality created by actual FR errors. Clearly a constant voltage characteristic (double power as impedance is halved) isn't that important in the overall scheme of things- but getting the distortion signature right is. That is why the tubes/transistors debate rages on ad nauseam.