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?  

Mr the Carbon what the frequency for crab chorus on slick Rick song Indian girl story? This one my test for speaker coherency chorus near end for adult audienceS.

Many claim to be, but how many can handle a full orchestra’s range?

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Since a  member here graciously posted a  link  revealing the fq range of a orchestra. 
FACTS of the matter is
60hz-2khz is the solid core of a  symphony instrumentation. 
How low, how high a  speaker does extend/does not extend is not at all to be considered in speaker choice consideration.
Its how well does a  speaker vouice this critical band width.
Wide Bnad high sensitivity is not beefy enough for voicing this band with a  significant force factor, = SLAM. 
The  cone material is too thin, there is not enough power to voice a  full orchestra.
Horns would be best bet, 
But there are 2 serious issues with horns
1) Big/heavy
2) Expensive
3) Ugly= Not wife friendly
This rules horns out.
back to xover designs. as the ultimate speaker for voicing orchestra.
The only cone material that works for me, is Seas Magnesium. I have not heard their newest Graphene cone, which may be a  improvement,  I have no idea, they are expensive.

Midwoofers voice the 40hz-1500/2khz.
Here is where a  orchestra's main  heart and soul is  voiced.

Tweeters only add a  shimmering

I have added a   4 inch wide band DavidLouis and this adds more body and fullness to the 80hz-12khz area, 
My Kasun  3.5 double magnet 91db paper cone tweeter adds sparkle, glitz to the 9khz-14khz

My next step is to find another DavidLouis that tops his 4 incher. 
I am happy with the 4, but I think we may get something more out his 6.5ers. 
His cone material on the 4 is not thin like the german labs, , it voices the muisc much different. The DL has soul, has warmth and  body.
Although the cone is like 3 inches, believe it or not, has some bass kick and  highs  roll off nicely at around 12k. 
My Frankenstein is full range  but w/o all the distortion issues you will find in speakers such as Vandersteen, 
Wilson
Focal
Kharma
Klipsch
ProAc
Sonus Faber
Tannoy
KEF
Revel
Harbeth
and countless others that suffer The Distortion Issue/Coloration in the critical bandwidth.
I have no such major issues in the criticals.
Only the DL 4 has some stress and mushiness at peak passages in orchestra.
I need to work getting a  new wide band 6.5 to make my Frankenstein the  best   possible speaker.
Sure horns will beat it, but the cost involved with horns, its not just practical. 

Just to be perfectly Clear - I am not disputing that normal human hearing range of a healthy individual ears is usually in-between 20Hz and 20kHz.

My take away from the info/ reports/articles, by various different sources
(there are several more) is that research has shown that in environments where Humans live the total frequency range at which soundwaves travel safe enough to have an affect on the Human condition is at the 15Hz - 150kHz.

Millercarbon is absolutely correct that at this level this would be at an unconscious condition at best.  So the argument then becomes - if this is true should it even be considered sound?

I have been convinced that it does. For the most basic fundamental reason that researchers know that frequency at this level  has a direct affect on the part Human brain that is specifically responsible for emotion.
Even in the unconscious condition.
 
What is music if not the greatest Human emotional expression.
What I also find interesting is the manufactures who embrace the science and incorporate it in their products - even if I can't afford it....

This link has a good visual along with brief bit well rounded explanation. You’ll notice that the instruments listed are set above a grand piano keyboard for reference.

I'm inclined, given the money I spend on my equipment, to want to hear all of the notes played so that I can feel the artists full expression of the piece they are playing.

An aside: You didn’t need subs for Rock until the Synth came along. But then you didn’t need 32hz until the Hammond B-3 became a regular in Rock, and before that 40hz was enough. 

https://www.psbspeakers.com/the-frequencies-of-music/