You may not always be able to hear them directly that well but you can hear the effect. Commentators say they can't hear the Townshend supertweeters at all when they put their ear up to them, but when they are turned off, the difference in the total sound field is quite marked. Apparently they work even if you don't have a lot of direct hearing above 10Khz, it is not a "direct hearing" kind of thing, more a matter of how the high frequencies effect the sound field and psychoacoustics.
Have a friend switch them in and out while you listen. If you really can't hear the difference, then its a long run for a short slide, but you should hear the difference.
Have a friend switch them in and out while you listen. If you really can't hear the difference, then its a long run for a short slide, but you should hear the difference.