How good's your hearing

Why do we need speakers w/20,000 hz frequency response?

One word, "harmonics" second, third, fourth can go well over 20khz.
My Plasma tweeter can go to 100khz!!!! boy can you hear it on harpsichord compared to just the ESL's, the highs just dance in space in front of you, you swear you can reach out and touch them,

Cheers George

For some reason I can’t get any links to post now. Just google ’musical instrument frequency chart’ and you’ll see that the violin’s frequency range is from 200 Hz to about 1.3Khz with harmonics out to about 17Khz and the flute is about 250Hz to around 3.2Khz with harmonics out to around 12Khz. so if you can hear them, you're not deficient in your hearing. 👍

All the best,
Nonoise

so if you can hear them, you're not deficient in your hearing. 👍

Not really, you may hear the fundamental but not hear the 2nd 3rd 4th harmonics. 

How about 'sense' it as your mind fills in the gaps? I ask because the harmonics start right where the actual range stops.

All the best,
Nonoise

2nd harmonic is double that of the fundamental, so if a piccolo’s fundamental is 4.2khz
2nd harmonic is 8.4khz,
3rd is 12.6khz
4th is 16.8khz
5th is 21khz
6th is 25.2khz
7th
8th
ect
ect

Destroy any of these, and you have destroyed it’s natural harmonic decay, your left with "gaps" in the music, which is a common Class-D complaint, as they have output filters to rid the switching noise that create phase shifts down to 3-5khz. 
Like when you puck a guitar string, it vibrates faster and faster as it decays away, stop it or change it and you've killed the natural harmonic decay.

Cheers George