A full range speaker?

millercarbon. Like you, I do think that inaudible upper frequencies matter; however, I have a hypothetical question: Is it possible that we do not necessarily know that our brains perceive this, and could these frequencies be used for directional location, i.e. placement of instruments.

That's a part of it for sure. My understanding is the ear has four times as many hair cells devoted to sensing frequencies above what we consider audible, as detect audible frequencies.  

This seeming paradox is resolved by the fact the so-called audible frequencies are all tested using sine waves. Something that really does not exist in nature. ggc is right, we evolved to find our way around a natural environment. It would make more sense to look there than at unnatural sine waves.  

In nature- which includes musical instruments- there are lots of things (like ggc's rain forests) that produce ultrasonic sounds. But unlike the test sine wave that exists unnaturally on its own, these are all mixed in with and riding on top of lower frequency fundamentals. When a leopard growls the powerful menacing part of the growl is down low. But the part that tells us how far and in which direction is for certain a lot higher in frequency.  

High frequencies attenuate with distance a lot faster than low frequencies. The frequency itself is enough to point us in the right direction. The balance of frequencies however can be used to tell us how far. It is to me just plain nuts to think we evolved over a billion years by staying alive, and yet somehow managed to do so never knowing how far away we are from being eaten. This is nuts. Absolutely nuts. 

For sure this stuff happens unconsciously. Has to. If we had to sit around thinking and analyzing we would be eaten alive. There is no time. There isn't even time for some of this to be processed in the cerebral cortex. Studies show that when shown an image of a snake the visual response time is faster than it would take neurons to go from the eye to the visual cortex. The response is, in other words, reflexive. There is no reason to think the same does not happen with sounds. Do predators hunt only in daylight?  

realworldaudio-

The brain makes sense of the fundamentals ONLY when the upper harmonic spectrum is correct. 

If true this would explain a number of things. It would explain whyTownshend Supertweeters improved the sound of instruments far lower in frequency than the Supertweeters output. It would explain why frequencies we cannot even hear as such nevertheless have an effect that can be heard. And it would account for the fact there are three times as many ear cells devoted to detecting these high frequencies than the ones we can hear.   

Maybe not explain, the question of why is always hard to crack, but it does for sure agree with all of these observations.

no driver moves anywhere near the distances you describe in generating that, so I think you mean distance time delay, and not pressure level peaks.

Good one. https://youtu.be/zt_HteJLY3A?t=73

I used to think such things mattered but now know very clearly they do not.

These specs are measured in anechoic chambers. So unless you listen in an anechoic chamber you can forget about that. Then since you are not in an anechoic chamber all the frequencies are reflecting everywhere creating nulls and modes where they are nullified and reinforced. This is especially bad the lower you go, where the lowest frequencies like you are talking literally criss-cross the room multiple times before you are even able to hear them. There’s psychoacoustic science behind all of this by the way.

Oh, and the top end is way more extended than you think. It extends far beyond 20kHz, to 40k at least if not 60k. No, you cannot hear that high. But instruments produce harmonics that high, which unless reproduced we lose fidelity. Change nothing else, simply add these back in, the whole presentation changes dramatically for the better. See my Townshend Maximum Supertweeter review and read others comments about supertweeters for more on that.

Really low bass, because of the physics of room dimensions, it really does not matter what anyone measures in their chamber it is nothing like what you are going to get at home. No two speakers ever made can do it. Physical impossibility. Unless in a vastly larger room or anechoic chamber.

What does work is multiple subs in multiple locations. With four subs it becomes very easy to achieve super clean articulate low bass. When this happens, another dramatic improvement in the presentation! Now since bass this low tricks our minds into believing we are in a large space the sound stage expands far beyond the room walls and starts to envelop us.

So that is what I think: we really do need everything from super low bass to beyond human hearing- only you cannot get it from any two speakers.   

With two speakers, two supertweeters, and four subs in a distributed bass array you can achieve full range in terms of frequency response. We still haven't touched on dynamic range, something I thought for sure you were going to ask about. But didn't.